Rozprawy doktorskie na temat „Organic Solar Cells, Conjugated Polymers, Organic Electronics”

Conjugated polymers are semiconducting materials that are currently being researched for numerous applications from chemical and biological sensors to electronic devices, including photovoltaics and transistors. Much of the novel research on conjugated polymers is performed in academic settings, where scientists are working to prepare conjugated polymers for commercially viable applications. By offering numerous advantages, inherent in macromolecular materials, conjugated polymers may hold the key to cheap and environmentally friendly manufacturing of future electronic devices. Mechanical flexibility, and solvent-based coating processes are two commonly cited advantages. Transitions in the backbone conformation of polythiophenes (PT) in organic solvents have been widely observed to influence thin-film morphology. However, conformational transitions of water-soluble PT derivatives, with respect to their intramolecular versus intermolecular origin, remain largely obscure. Here, conformational transitions of a water- soluble polythiophene in aqueous ionic surfactants are investigated by means of Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), polarizing optical microscopy (POM), ultraviolet-visible (UV-Vis) absorption and fluorescence spectroscopy, and various X-ray scattering techniques. As-prepared complexes exist as stable hydrogels. Upon dilution, a significant time-dependent chromism occurs spontaneously. A coil-to-rod conformational transition is identified in this mechanism and verified using small-angle x-ray scattering (SAXS). Study into the corresponding kinetics demonstrates an inverse first-order rate law. It is found that the conformational transition is thermally reversible and concentration-independent. The critical transition temperature is largely dependent on the surfactant formulation. A theoretical model is presented to explain this new phenomenon and the mechanisms behind its influence on the optoelectronic and solid-state morphological properties. A relationship between the dilute-solution processing with surfactants and the final properties of the system is substantiated.

Organic photovoltaics have attracted considerable research and commercial interest due to their lightness, mechanical flexibility and low production costs. There are two main approaches for the fabrication of organic solar cells – solution and vacuum processing. The former relies on morphology control in polymer-fullerene blends resulting from natural phase separation in these systems. The latter takes advantage of solvent-free processing allowing highly complex multi-junction architectures similar to inorganic solar cells. This work aims to combine the benefits of both by depositing conjugated polymers using vacuum thermal evaporation. By employing this unconventional approach it aims to enhance the efficiency of organic photovoltaics through increased complexity of the thin-film architecture while improving the nanoscale morphology control of the individual active layers. The thesis explores the vacuum thermal deposition of polythiophenes, mainly poly(3-hexylthiophene) (P3HT) and side-group free poly(thiophene) (PTh). A variety of chemical techniques, such as NMR, FT-IR, GPC, DSC and TGA, are used to examine the effect of heating on chemical structure of the polymers. Optimal processing parameters are identified and related to the resulting thin-film morphology and charge transport properties. Efficient photovoltaic devices based on polythiophene donors and fullerene acceptors are fabricated. Materials science techniques AFM, XRD, SEM, TEM and MicroXAM are used to characterize topography and morphology of the thin films, and UV-Vis, EQE, I-V and C-V measurements relate these to the optical and electronic properties. The results of the study show that polymer side groups have a strong influence on molecular packing and charge extraction in vacuum-deposited polymer thin films. Unlike P3HT, evaporated PTh forms highly crystalline films. This leads to enhanced charge transport properties with hole mobility two orders of magnitude higher than that in P3HT. The effect of molecular order is demonstrated on polymer/fullerene planar heterojunction solar cells. PTh-based devices have significantly better current and recombination characteristics, resulting in improved overall power conversion efficiency (PCE) by 70% as compared to P3HT. This confirms that the chemical structure of the molecule is a crucial parameter in deposition of large organic semiconductors. It is also the first-ever example of vacuum-deposited polymer photovoltaic cell. Next, vacuum co-deposited PTh:C60 bulk heterojunctions with different donor-acceptor compositions are fabricated, and the effect of post-production thermal annealing on their photovoltaic performance and morphology is studied. Co-deposition of blended mixtures leads to 60% higher photocurrents than in thickness-optimized PTh/C60 planar heterojunction counterparts. Furthermore, by annealing the devices post-situ the PCE is improved by as much as 80%, achieving performance comparable to previously reported polythiophene and oligothiophene equivalents processed in solution and vacuum, respectively. The enhanced photo-response is a result of favourable morphological development of PTh upon annealing. In contrast to standard vacuum-processed molecular blends, annealing-induced phase separation in PTh:C60 does not lead to the formation of coarse morphology but rather to an incremental improvement of the already established interpenetrated nanoscale network. The morphological response of the evaporated PTh within the blend is further verified to positively differ from that of its small-molecule counterpart sexithiophene. This illustrates the morphological advantage of polymer-fullerene combination over all other vacuum-processable material systems. In conclusion, this processing approach outlines the conceptual path towards the most beneficial combination of solution/polymer- and vacuum-based photovoltaics. It opens up a fabrication method with considerable potential to enhance the efficiency of large-scale organic solar cells production.

Les cellules photovoltaïques organiques ont fait l'objet d'un intérêt croissant au cours de ces dernières décennies car elles offrent un grand potentiel pour une production d'énergie renouvelable à faible coût. Afin d'obtenir des cellules solaires organiques à haut rendement de conversion d'énergie, beaucoup de recherches se focalisent sur les matériaux ayant des capacités à absorber la lumière efficacement. Dans ce contexte, le présent travail se concentre sur la conception et le développement de nouveaux matériaux donneurs d'électrons (oligomères et polymères) comme matériaux absorbant de la lumière basée sur l'approche « Donneur-Accepteur » alternant des segments riches en électron (donneur d'électron) et des unités pauvres en électron (accepteur d'électron). Trois séries d'unités riches en électron ont été étudiées: oligothiophènes, fluorène et indacenodithiophene. L'unité fluorénone est la principale unité « accepteur d'électron » étudiée. Une comparaison directe avec le système basé sur l'unité benzothiadiazole comme accepteur d'électron est également rapportée. Trois méthodes principales de synthèse ont été utilisées: polymérisation oxydante par le chlorure de fer (III), et les couplages croisés au palladium de type Suzuki ou de Stille. Les études spectroscopique UV-Visible en absorption et en photoluminescence sur ces oligomères et polymères ont démontré la présence de complexes à transfert de charges permettant d'élargir le spectre d'absorption. Les oligomères et les polymères possèdent des faibles largeurs de bande interdite de 1,6 eV à 2 eV. Les systèmes ayant des unités fluorénones présentent des spectres d'absorption étendus allant jusqu'à 600-700 nm, tandis que les systèmes ayant des unités benzothiadiazoles présentent des spectres d'absorption allant jusqu'à 700- 800 nm. La nature des bandes de complexes à transfert de charge se révèle d'être dépendant de la force de respective des unités « donneur d'électrons » et des unités « accepteur d'électrons ». Les niveaux d'énergies HOMO et LUMO des oligomères et les polymères sont déterminés par des mesures électrochimiques. Les polymères à base de fluorène possèdent des niveaux d'énergie HOMO les plus bas. Ces polymères testés en mélange avec les fullerenes PCBM en cellules photovoltaïques ont démontré des valeurs élevées de tension en circuit ouvert (Voc) proche de 0,9 V. Tous les oligomères et les polymères ont été testés dans des dispositifs photovoltaïques et ont montré des résultats encourageants avec des rendements de conversion allant jusqu'à 2,1 %. Ce sont des premièrs résultats obtenus après seulement quelques optimisations (ratios oligomères ou polymères : fullerènes et recuit thermique). Ce travail prometteur permet ainsi d'envisager des résultats plus élevés dans le futur
Organic photovoltaic (OPV) cells have been a subject of increasing interest during the last decade as they are promising candidates for low cost renewable energy production. In order to obtain reasonably high performance organic solar cells, development of efficient light absorbing materials are of primary focus in the OPV field. In this context, the present work is focused on the design and development of new electron donor materials (oligomers and polymers) as light absorbing materials based on “Donor-Acceptor” approach alternating electron donating group and electron withdrawing group. Three main families of electron donating group are studied: oligothiophenes, fluorene and indacenodithiophene. Fluorenone unit is the principal electron withdrawing group studied and a direct comparison with the system based on benzothiadiazole unit as electron withdrawing unit is also provided. Three main synthetic methods were employed: oxidative polymerization mediated by Iron (III) chloride and Palladium cross-coupling reactions according to Suzuki coupling or Stille coupling conditions. Spectroscopic studies on absorption and photoluminescence have demonstrated the presence of characteristic charge transfer complex in all the studied D-A oligomers and polymers allowing the extension of the absorption spectrum. The D-A oligomers and polymers have shown an overall low optical band gap of 1.6-2 eV with absorption spectra up to 600 to 800 nm. The nature of the charge transfer complex transitions bands were found to be depending on the strength of the electron donating unit and the electron withdrawing unit. Furthermore molecular packing in solution and in solid state has also demonstrated to contribute to extension of absorption spectrum. The HOMO and LUMO energy levels of the oligomers and polymers were determined by electrochemical measurements. Fluorene-based polymers have shown low lying HOMO energy levels, and these polymers demonstrate high open circuit voltage (Voc) in photovoltaic cell when combined with fullerenes derivatives PCBM with Voc values close to 0.9 V. The oligomers and polymers tested in photovoltaic devices have shown promising results with the highest power conversion efficiency obtained of 2.1 % when combined with fullerenes PCBMC70. These results were obtained after only limited numbers of device optimizations such as the active materials ratios and thermal annealing. Therefore further optimization of devices may exhibit higher power conversion efficiencies

This thesis is dedicated to developing conjugated polymer and small-molecule donor materials for solution-processable organic solar cells. To begin with, a brief introduction of organic solar cells (OSCs) and an overview of donor materials development were presented in Chapter 1. In chapter 2, we used carbon-carbon triple bands as linkage of the TVT unit to develop a new building block, ATVTA. Small molecules S-03, S-04, and S-05 with ATVTA as building block showed broad absorption spectra and low-lying HOMO energy levels. S-01 with TVT unit and S-02 with AT2 as building block were also synthesized for clear comparison. OSCs devices based on S-01 and S-02 showed a Voc of 0.88 V and 0.89 V, respectively. The device based on S-03 exhibited a high Voc of 0.96 V, leading to a PCE of 2.19%. The devices based on S-04 and S-05 afforded a notable Voc over 1.0 V. The results demonstrate that ATVTA unit is a promising building block for extending π conjugation of the molecules without pulling up their HOMO energy levels. Chapter 3 focused on the development of 2D-conjugated small-molecule donor materials. The 2D-conjugated small molecule S-06 possesses excellent solution processability, broad absorption feature, respectable hole mobility and good film-forming morphology. The conjugated thiophene side chain not only effectively extends the absorption spectrum, but also lowers the HOMO energy level, which is desirable for obtaining high Voc. The BHJ OSCs based on S-06:PC70BM (1:0.5, w/w) afforded a high PCE of 4.0% and a notable FF of 0.63 without any special treatment needed. This preliminary work demonstrates that this kind of 2D-conjugated small molecules offer a good strategy to design new photovoltaic small molecule-based donor materials with high FF and Voc for high-efficiency OSCs. The consistently developed two 2D-conjugated small molecules S-07 and S-08 also possess low-lying HOMO energy levels. OSC device based on S-07:PC60BM (1:3, w/w) afforded a notable Voc of 0.96 V, with a PCE of 2.52%. BHJ devices based on S-08 will be fabricated and tested to investigate its photovoltaic properties in the near future. We developed a series of oligothiophenes with platinum(Ⅱ) as the building block in Chapter 4. These small metallated conjugated small molecules exhibited broad spectra and relatively low-lying HOMO energy levels in the range of –5.27 eV to –5.40 eV. Introducing platinum(Ⅱ) arylene ethynylenes as building block can be considered as an approach to obtain small-molecule donors with satisfactory absorption features and HOMO energy levels. Nevertheless, due to the low FF, the PCEs of these donor materials based devices are lower than 2%. Fine tuning the film morphologies of this kind of metallated small-molecule donor materials should be carried out to improve their photovoltaic performance. We addressed an efficient approach to improve the photovoltaic properties by side chain engineering in 2D-conjugated polymers in Chapter 5. Considering the fact that the Voc of PBDTTT based devices is less than 0.8 V, we introduced alkylthio substituent on the conjugated thiophene side chains of the 2D-conjugated copolymer to further improve the photovoltaic performance of the 2D-conjugated copolymers PBDTTTs. The weak electron-donating ability of the alkylthio side chains effectively down-shifted the HOMO energy level of PBDTT-S-TT by 0.11 eV in comparison to the corresponding polymer with alkyl substitution on the conjugated thiophene side chains. The PSC device based on PBDTT-S-TT showed an enhanced Voc of 0.84 V, which is among the highest one in the reported copolymers based on BDT and TT units, leading to an enhanced PCE of 8.42%. The results indicate that molecular modification by introducing alkylthio side chain will be a promising strategy to broaden the absorption, down-shift the HOMO energy level and increase the hole mobility of the low band gap 2D-conjugated polymers for further enhancing the photovoltaic performance of PSCs. PBDTT-O-TT-C and PBDTT-S-TT-C were developed to further study the conclusion. We found that OSC device based on PBDTT-S-TT-C with alkylthio side chain also demonstrated a high Voc of 0.89 V, with a PCE of 6.85% when processed with 3% DIO additive

The effect of light exposure in ambient air on thin films made from an electron acceptor polymer poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (N2200), an electron donor polymer Poly[[2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl]-2,5-thiophenediyl] (TQ1) and their blends, has been studied using UV-vis spectroscopy and Atomic Force Microscopy (AFM). For solutions of TQ1, N2200 and blends, the linearity of the Beer-Lambert law for absorption spectroscopy has been verified. The measured UV-vis spectra show that TQ1 thin films are more sensitive to degradation by simulated sunlight than N2200 films. They also show that among the polymer blends, the N2200-rich blend with volume ratio 1:2 (TQ1:N2200) was less sensitive to degradation by simulated sunlight than blends of ratio 1:1 and 2:1. The AFM images showed a change in roughness between the undegraded and degraded films, where the TQ1, 1:1 and 1:2 films obtained lower roughness after 45 hours of degradation, and the N2200 and the 2:1 films obtained higher roughness.
Effekten av simulerad solljusexponering i omgivande luft på tunna filmer gjorda av en elektronaccepterande polymer poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (N2200), en elektrondonerande polymer Poly[[2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl]-2,5-thiophenediyl] (TQ1) och deras blandningar, har undersökts genom ultraviolett-synlig-spektroskopi (UV-vis-spektroskopi) och atomkraftsmikroskopi (AFM). Genom lösningar av TQ1, N2200 och blandningar, har det linjära förhållandet i Beer Lamberts lag för absorptionsspektroskopi verifierats. De mätta UV-vis-spektrumen visar att tunna TQ1-filmer är känsligare mot degradering genom simulerat solljus än tunna N2200-filmer. De visar också att den N2200-rika blandningen med ett volymförhållande av 1:2 (TQ1:N2200) var mindre känslig för degradering av simulerat solljus än blandningar med volymförhållandet 1:1 och 2:1. AFM-bilderna visade en förändring i råhet mellan degraderade och icke-degraderade filmer, där TQ1-, 1:1-, och 1:2-filmerna fick en lägre ytråhet efter 45 timmar av degradering, och N2200- och 2:1-filmera fick en högre ytråhet.

This thesis described the synthesis and characterization of new perylene diimide (PDI)-based photonic and electronic materials. In the first part of this thesis, PDI-based polynorbornenes, including PDI-grafted homopolymers and block-copolymers (BCPs) were synthesized and characterized as alternative acceptors for fullerenes for organic electronics. It was found that the PDIs on the polymer side-chains affect π-π stacking with the neighboring PDIs, which has implications for the use of these materials for organic field-effect transistors (OFETs) and organic photovoltaic devices (OPVs). It should be noted that the performance of solar cell based on these materials was poor, like other similar materials. The major reasons could be the challenge in controlling the molecular alignment of the PDI-based materials, which leads to lower electron mobilities in films compared to devices with fullerene-based acceptors. One PDI-grafted BCP showed better OPV performance compared to the other BCPs and respective homepolymer blends, presumably due to favorable morphology. In the second part of this thesis, photo-induced charge-separation in blends of poly-3-hexyl-thiophene (P3HT) and various PDI derivatives have been studied. Probing of long-lived photo-generated PDI radical anions provided insight on these photo-induced processes and their use for OPVs. In the third part of this thesis, the use of photo-generated PDI radical-anion absorption was shown to be effective for optical limiting of nanosecond laser pulses between 650 - 800 nm. In Chapter 5, an effective approach for two-photon absorption (2PA)-induced optical limiting using donor-PDI dyads through which donors and acceptors can be independently chosen to maximize optical suppression at particular wavelengths has been demonstrated. In Chapter 6, conjugated polymers with PDI pendants and poly(carbazole-alt-2,7-fluorene) main-chains were synthesized for optical limiting using the photo-generated PDI radical anion via PDI aggregate excitation and/or 2PA from the polymer backbones. It was also found that nitro-phenyl group or similar derivatives could be good candidates to incorporate into those donor-conjugated polymers, which have significant overlap between their 2PA band and respective polaron absorptions for 2PA-indced optical limiting.
Thesis advisor has approved the addition of errata to this item. Corrections were made to pages 95, 98 and 101.

New technologies for photovoltaic energy generation can contribute to environmentally friendly, renewable energy production and may lead to the reduction of carbon dioxide liberated by burning fossil fuels and biomasses. Besides the established silicon based solar cells new photovoltaic technology has gained a lot of interest during the last decade. Among them organic solar cells (OSC) based on conjugated molecules or polymers are promising candidates for the manufacturing of environmentally safe, flexible, lightweight, and inexpensive photovoltaic devices which can be used in low cost applications. Particularly attractives are in photovoltaic (PV) elements based on thin plastic films. The flexibility offered through the chemical tailoring of desired properties, as well as the cheap technology already well developed for all kinds of plastic thin film applications would make such an approach widely adopted. Unfortunately a main bottleneck is to be solved before industrial production could become economically viable, particularly represented by the still low conversion efficiency. In organic semiconductors the primary photo-excitations do not directly and quantitatively lead to free charge carriers but to coulombically bound electron-hole pairs, called excitons, that need strong electric fields to generated free charge carriers, present for example at the discontinuous potential drops at the interfaces between donors and acceptors as well as between semiconductors and metals. The exciton diffusion lengths in polymers and in organic semiconductors is usually around 10-20 nm: for efficient photovoltaic devices, the excitons have to split before recombining and the free electrons and holes must be transported towards the electrodes to produce the photocurrent. Major problem derives from loss mechanism, such as exciton decay, charge recombination and low mobility, resulting in reduced photocurrent extraction at the electrodes and low power conversion efficiency. The improvement of the efficiency is one of the most important aspect in which is concentrated the research in OSC, our too. Two different routes going towards this objective focalized in this aspect have been explored, in order to contribute to realize a novel and effective technology in the photovoltaic field. The first concerns the development of a novel light trapping system bases on microlenses, The second, on which we are still working, regards the fabrication of nanostructured solar cells by top-down techniques, particularly nanoimprinting (NIL).
Il problema energetico sta destando negli ultimi anni sempre maggior interesse e preoccupazione, per il ridursi delle risorse fossili e dal conseguente acuirsi dei problemi d’inquinamento derivanti dal loro quasi esclusivo utilizzo per la produzione di energia elettrica. Non è sorprendente quindi che dal mondo della ricerca un grande sforzo sia dedicato allo sviluppo della tecnologia fotovoltaica. Attualmente, il silicio possiede una posizione centrale nel panorama delle celle fotovoltaiche: l’elevato costo di questo tipo di tecnologia, derivato dall’alto costo del materiale e dei processi fabbricativi, ha incoraggiato lo sviluppo di soluzioni alternative che si basino su materiali innovativi. Tra queste, grande risalto è stato dato negli ultimi anni alle cosiddette "organic solar cell", basate sull’impiego di semiconduttori organici. Il loro vantaggio risiede nel fatto che questi possono essere depositati, su larghe aree e a costi molto ridotti, in fase liquida, utilizzando quindi metodi tipici dell’industria della stampa nel campo del fotovoltaico ed eliminando così alti costi di materiale e di processo tipici dell’industria a semiconduttore inorganico. L’impiego di film sottili e conseguentemente di poco materiale, contribuisce a rendere il fotovoltaico organico uno dei più quotati candidati per lo sviluppo di una tecnologia solare a basso costo. Una tipologia di celle solari organiche utilizza come materiali foto attivi i polimeri coniugati; evidenti progressi sono stati compiuti, col raggiungimento di efficienze ragguardevoli, dell’ordine del 4-5%. Purtroppo però, questo non è ancora sufficiente perché la tecnologia possa essere trasferita su scala industriale. Molti sforzi si stanno facendo nell’ambito della ricerca per migliorare l’efficienza di queste celle. Sullo sviluppo e l’impiego di soluzioni alternative e innovative applicabili al campo del fotovoltaico organico, e in particolare polimerico, è concentrata la nostra attività di ricerca. Due percorsi in particolare sono stati investigati, basate sull’impiego di un nuovo sistema per l’intrappolamento in cavità della luce e sull’impiego delle nanotecnologie fabbricative.

The world energy consumption is increasing at an average rate of 2.1 % per year, spurred by the economic growth in most of Asian countries, Europe and Canada. The consequent depletion of fossil fuels reservoirs and the reinforced need of environmental sustainability are making the challenge of clean and renewable energy sources one of the most urgent challenges for humankind. Solar power is among the best candidates for the leading role in the energy revolution, being clean, infinite and well distributed over the planet. For this reason, photovoltaic technologies for electricity production are gaining increasing popularity. Although inorganic silicon solar cells dominate the market of photovoltaics, organic and hybrid materials attract considerable interest since their properties like flexibility, light-weight, transparency and low-cost could make the difference in the raising of solar electricity. So far, these materials could not yet outperform conventional silicon, stimulating intensive scientific research on both the development of new materials and the understanding of the photophysical mechanisms governing the photovoltaic behavior of organic/hybrid semiconductors. In this thesis, a series of new organic and hybrid photoactive materials is studied using Electron Paramagnetic Resonance spectroscopy (EPR). This technique, combined with photoexcitation, allows to unambiguously characterize the photoinduced processes involving the formation of paramagnetic states like radicals and triplet states. As shown in the thesis, EPR can also give useful information about molecular ordering in the materials, which is known to be intimately connected with charge transport properties. Conjugated polymers are known for their semiconducting properties and their blends with strong electron accepting fullerene derivatives are among the best performing organic photovoltaic systems. Donor-acceptor alternating copolymers have been introduced to enhance the light-harvesting properties of the blends. Compared to homopolymers, they usually display a lower crystallinity of the deposited films. Thus, XRD techniques are often not suitable to investigate their molecular ordering features. We apply EPR to the analysis of molecular orientational order in the films of two polymers representative of this class, showing that a consistent degree of preferential orientation occurs with two common deposition methods. Fullerene-free materials for polymer solar cells have been recently introduced and overcome some of the drawbacks of fullerene acceptors like the limited absorption and the poor bandgap tunability. In this framework, we study two blends of electron-donor and acceptor polymers to probe their properties with respect to the common fullerene/donor combination, showing that they avoid charge recombination to triplet states which is an active loss mechanism in fullerene-containing blends. Furthermore, the all-polymer films provide a high degree of orientational order and efficient interaction between the donor and acceptor phases that make them promising alternatives to polymer-fullerene blends. A reduced graphene oxide-triphenylamine covalently-linked nanohybrid is studied as potential photosensitizer for TiO2 in dye-sensitized solar cells, able to improve the conductivity and the stability of the system. EPR shows that efficient photoinduced electron transfer from the sensitizer to the semiconductor occurs, paving the way to this new class of photosensitizers. Finally, we investigate the photoactivity of a supramolecular soft-material, forming a gel, composed of small self-assembling donor and acceptor molecules. In this case, EPR allows to verify the efficiency of charge transport across the supramolecular structures, suggesting appealing semiconducting properties of the material. The results of this thesis show the relevance of EPR for unraveling functional and morphological properties of photovoltaic materials and provide a useful characterization of the photophysics of new systems that may be further explored to bring substantial progresses to the field of organic photovoltaics.
Il consumo mondiale di energia ha un tasso medio di crescita del 2.1 % all’anno, trainato dalla crescita economica di molti Paesi asiatici, dell’Europa e del Canada. Il conseguente depauperamento delle risorse di combustibili fossili e il più stringente bisogno di proteggere l’ambiente stanno facendo della sfida delle energie rinnovabili una delle più urgenti sfide che l’umanità deve affrontare. L’energia solare è tra i migliori candidati a svolgere il ruolo di punta nella rivoluzione energetica, essendo una fonte di energia pulita, infinita e ben distribuita nel pianeta. Per questo motivo le tecnologie fotovoltaiche per la produzione di energia elettrica stanno acquistando crescente popolarità. Sebbene le celle solari a base di Silicio dominino il mercato del fotovoltaico, materiali organici e ibridi sono fonte di crescente interesse grazie alle loro peculiari proprietà, come la flessibilità, la leggerezza e la trasparenza, il basso costo, che ci si aspetta possano fare la differenza nell’affermazione del fotovoltaico. Fino ad ora questi materiali non hanno superato il rendimento dei materiali convenzionali a base di Silicio, stimolando la ricerca scientifica verso lo sviluppo di nuovi materiali e lo studio dei meccanismi fotofisici che governano il comportamento fotovoltaico dei semiconduttori organici e ibridi. In questa tesi, una serie di nuovi materiali fotoattivi, organici e ibridi, è stata studiata utilizzando la spettroscopia di Risonanza Paramagnetica Elettronica (EPR). Tale tecnica, combinata con la fotoeccitazione, permette di caratterizzare i processi fotoindotti che portano alla formazione di stati paramagnetici come radicali e stati di tripletto. Come mostrato nella tesi, la tecnica EPR può essere anche utilizzata per ottenere informazioni circa l’ordine molecolare nei materiali, che è noto essere strettamente collegato alle loro proprietà di trasporto di carica. I polimeri coniugati sono noti per le loro proprietà di semiconduttori e le loro miscele con derivati fullereneci - forti electron-accettori - sono tra i sistemi fotovoltaici organici più efficienti. Copolimeri alternanti composti da unità elettron-accettrici e donatrici sono stati introdotti per aumentare l’efficienza di assorbimento dello spettro solare. Rispetto ai classici omopolimeri, questi mostrano solitamente una minore cristallinità dei film depositati. Pertanto, tecniche diffrattometriche si rivelano spesso inadeguate per caratterizzarne l’ordine molecolare. In questa tesi l’EPR viene utilizzato per analizzare l’ordine orientazionale in due polimeri rappresentativi di questa classe, mostrando che un grado consistente di orientazione preferenziale è presente nei film ottenuti con due diverse tecniche di deposizione. Materiali fullerene-free per le celle solari polimeriche sono stati recentemente introdotti per superare alcuni degli svantaggi degli accettori fullerenici, come il limitato assorbimento della luce solare e la difficoltà nel regolare il bandgap e le proprietà elettroniche. In questo conteso, abbiamo studiato due blend costituiti da polimeri elettron-accettori e donatori al fine di investigarne le proprietà e di compararle a quelle dei convenzionali blend di polimeri donatori con derivati fullerenici, dimostrando che essi eliminano la ricombinazione di cariche a formare stati di tripletto, meccanismo noto come fonte di perdita di efficienza nei materiali contenti fullereni. Inoltre, i film polimerici mostrano un elevato grado di ordine orientazionale e un’efficiente interazione tra le fasi di donatore e di accettore che li rendono promettenti alternative ai blend di polimero e fullerene. Un nanoibrido composto da grafene ossido ridotto e molecole di trifenilammina legati covalentemente, è stato studiato come potenziale colorante per la titania in celle solari sensibilizzate a colorante, capace di migliorare la conducibilità e la stabilità del sistema. L’EPR ha mostrato che un efficiente trasferimento elettronico fotoindotto avviene tra l’ibrido e il semiconduttore, aprendo la strada all’applicazione di una nuova classe di coloranti. Infine, la fotoattività di un materiale supramolecolare, un gel composto da piccole molecole di donatore e accettore che autoassemblano, è stata studiata. In questo caso l’EPR ha permesso di verificare un efficiente trasporto di carica attraverso le strutture supramolecolari, suggerendo interessanti proprietà semiconduttive del materiale. I risultati di questa tesi dimostrano la rilevanza dell’EPR per l’indagine su aspetti funzionali e morfologici di materiali fotovoltaici e forniscono una caratterizzazione della fotofisica di nuovi sistemi che potrebbero essere ulteriormente esplorati per apportare progressi sostanziali nel campo del fotovoltaico organico e ibrido.

This diploma thesis concentrates on the properties characterization of new organic materials for solar cells. In the theoretical part, there is a solar cells themed literature search, there is described a mechanism of conversion of solar energy, factors influencing photovoltaic conversion efficiency and materials using for preparation of organic solar cells. The practical part includes the preparation of solar cells and characterization of optical and electrical properties of the studied materials in thin layers and solutions. Used materials were conjugated polymers and derivatives of fullerenes.

No estudo de sistemas híbridos orgânico-inorgânico, o uso de materiais como polímeros conjugados e óxidos de metal de transição tem despertado grande interes- se. Em particular, destacam-se sistemas compostos de tiofenos e óxido de titânio, que encontram uma importante aplicação em células solares. Para um melhor entendimento da interação entre os dois sistemas, torna-se necessário conhecer a organização do polímero sobre o substrato inorgânico. Desse modo, investigamos neste trabalho a formação da interface entre oligômeros de tiofeno e a superfície (101) de TiO2-anatase utilizando um enfoque de multiformalismo, que inclui simulações de dinâmica molecular clássica, e uma combinação de cálculos de primeiros princípios segundo Hartree-Fock e Teoria do Funcional da Densidade (DFT) para a determinação de propriedades estruturais e eletrônicas. A deposição de oligômeros de tiofeno sobre TiO2, constituindo sistemas de milhares de átomos, foi simulada por meio de dinâmica molecular clássica. Como requisito do cálculo clássico para estes sistemas, realizamos a reparametrização do campo de forças Universal tanto para os oligômeros, cujas estruturas não são bem descritas pelos campos de força padrões, como para o cristal e a superfície de TiO2. Foi observada a formação de filmes desordenados e densos de quatertiofeno, com a presença de uma maioria de moléculas de orientação quase perpendicular em relação ao plano superficial. Na camada de interface também se encontram moléculas dispostas paralelamente ao substrato, aumentando o contato entre os sistemas orgânico e inorgânico. A deposição de oligômeros isolados de quatertiofeno e de hexatiofeno mostra ainda que as moléculas se dispõem paralelas na superfície, alinhadas segundo direções de periodicidade dos átomos da superfície. Estudamos desta forma as propriedades eletrônicas de um sistema composto de politiofeno sobre TiO2, com o polímero paralelo na superfície e disposto na direção preferencial, através de um formalismo ab initio DFT. Apesar do tratamento DFT apresentar problemas conhecidos quanto na definição do gap, o que é mais relevante ainda no nosso caso de sistemas híbridos, os resultados revelam um deslocamento do topo da banda de valência do material orgânico em relação ao inorgânico. Isto possibilita o aprisionamento de um buraco no polímero, condição necessária para o uso deste tipo de sistema em células fotovoltaicas. Verifica-se ainda o acoplamento entre átomos de enxofre do politiofeno e de oxigênio do TiO2 através da presença de um estado associado a uma densidade eletrônica que se estende do polímero na superfície. Nossos resultados indicam assim um bom acoplamento eletrônico da superfície (101) de TiO2-anatase com politiofenos.
In the study of organic-inorganic hybrid systems, the use of materials such as conjugated polymers and transition metal oxides has attracted great interest. In particular, it is worth mentioning systems composed by thiophenes and titanium oxide, which have an important application in solar cells. For a better understand- ing of the interaction between these systems, it is necessary to know the polymer organization over the inorganic substrate. Therefore, we investigated in this work the formation of the interface between thiophene oligomers and the (101) surface of TiO2-anatase by means of a multi-formalism approach, which includes classical molecular dynamics simulations, and a combination of ¯rst principles calculations based on Hartree-Fock and Density Functional Theory (DFT) for structural and electronic properties. The simulation of deposition of thiophene oligomers on TiO2, which demands systems with thousands of atoms, was performed by classical molecular dynamics. As a prerequisite for the classical calculation for these systems, we performed a re-parameterization of the Universal force ¯eld for the oligomers, whose structures are not well described by standard force ¯elds, and for the TiO2 bulk and surface. We observed the formation of disordered and dense quaterthiophene ¯lms, with presence of a majority of molecules oriented almost perpendicularly to the surface plane. In the ¯rst interfacial layer we ¯nd also molecules oriented parallel to the sub- strate, which increases the contact between the organic and the inorganic systems. The deposition of isolated quaterthiophene and sexithiophene oligomers resulted in molecules disposed parallel to the surface and aligned along directions of periodicity of the surface atoms. We therefore studied the electronic properties of a system composed of poly- thiophene on TiO2, with the polymer parallel to the surface and oriented along a preferential direction, by means of DFT formalism. Although DFT treatments present known problems in the de¯nition of the energy gap, even of more relevance in our case of hybrid systems, the results for the occupied states revealed a sizeable displacement of the top of the valence band of one system with respect to the other. The misalignment will prevent the passage of a hole from the polymer to the oxide, providing in this way the necessary condition for the use of this type of system in solar cells. It was also seen electronic coupling between sulfur atoms from polythio- phene, and oxygen atoms from TiO2 through the presence of a state associated with an electronic density extended from the polymer to the surface. Our results thus indicate there is good electronic coupling between the (101) surface of TiO2-anatase and polythiophenes.

The interest in the detail knowledge about elementary electronic processes during photogeneration of charge carriers, which allow achieving higher efficiency of organic solar cells, grows with advent of the commercial organic solar cells production. The thesis is focused on study of photogeneration of charge carriers in organic semiconductors, especially in -conjugated polymer materials. First part of the thesis summarized state of the art in studies of photogeneration of charge carriers in polymer solar cells. Subsequent experimental and results part are focused on study of polymeric solar cells prepared from electron donor polymers MDMO-PPV, Tg-PPV, PCDTBT and PCBTDPP and electron acceptor derivates of fullerenes PC60BM and PC70BM. Results of the thesis are divided in tree main parts: 1) study of charge transfer between electron donor and electron acceptor materials by optical methods, 2) study of charge transfer between electron donor and electron acceptor materials by optoelectrical methods and 3) development of organic solar cells on flexible substrates. The last part is focused largely on deposition methods of active materials thin layer.

The investigation carried out in this project allowed for the development of eleven regioregular π-conjugated alternating copolymers and their implementation in organic solar cells. The eleven synthesized polymers, poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(4,7-dithien-2-yl-2,1,3-benzothiadiazole)] (CB), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(1,6-pyrene)] (LP), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(5,5’’’-(3,3’’’-dihexyl-2,2':5',2'':5'',2'''-quarterthiophene))] (CT), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(2,7-9H-fluoren-9-one)] (CF), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(1,6-pyrene)] (CP), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(4,7-dithien-2-yl-2,1,3-benzothiadiazole)] (LB), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(2,7-9H-fluoren-9-one)] (LF), poly[(5,5’’’-(3,3’’’-dihexyl-2,2':5',2'':5'',2'''-quarterthiophene))-alt-(2,7-9H- fluoren-9-one)] (TF), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(4,4'-dioctyl-2,2'-bithiophene)] (oTLT), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(4,4'-dioctyl-2,2'-bithiophene)] (oTCT), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(4,4'-dihexyl-2,2'-bithiophene)] (TCT), were investigated using theoretical methods that included semi-empirical geometry optimizations, density functional theory (DFT) energy calculations, and time-dependent density functional theory (TD-DFT) optical absorption predictions. The absorption predictions gave credence to our experimental results in which the absorption of the longer polymer chains underwent a redshift from the monomer absorption. With several of the prepared polymers, bulk-heterojunction photovoltaic cells were fabricated and their photovoltaic activity was investigated. Several of the fabricated cells exhibited photovoltaic efficiencies including polymer/PCBM composites with an aluminum back electrode (CF, CT, P3HT, and MEH-PPV), and also inverted cells with a silver back electrode (CT, P3HT, and MEH-PPV). Several polymers (CF, CT, TCT, LP, oTCT, oTLT, P3HT, and MEH-PPV) were used to solubilize single-walled carbon nanotubes (SWNTs). The solubility of the nanotubes occurred by the polymers’ ability to wrap the tubes, disrupt the bundles (ropes of tubes), and allow for the creation of a homogeneous mixture. Polymer:PCBM:SWNT mixtures were prepared and utilized as the active layer in BHJ solar cells. Some of the inverted cells (with a silver back electrode) that incorporated the nanotube composites (CT, oTCT, oTLT, P3HT, and MEH-PPV) displayed photovoltaic activity. These preliminary results illuminate the photovoltaic behavior of the polymer and provide evidence for their future use in polymer solar cells.
Thesis (Master, Chemistry) -- Queen's University, 2011-02-13 22:09:00.464

The present thesis is focused on the rational design of Diketopyrrolopyrrole based π- conjugated polymers for organic electronics. The thesis is organized into six different chapters and a brief description of the individual chapters is provided below. Chapter 1 briefly describes the physics governing the electronic processes occurring in organic photovoltaics (OPVs) and organic field-effect transistors (OFETs) followed by design rules for the synthesis of conjugated polymers for organic electronics. Diketopyrrolopyrrole (DPP) based π-conjugated materials and their development in OPVs and OFETs have been highlighted. Chapter 2 discusses the synthesis and characterization of a series of small molecules of DPP derivatives attached with different alkyl chains. Influence of side chains on the photophysical properties of these DPP derivatives have been studied by UV-visible spectroscopy and DFT calculations. Crystal structure studies revealed the effect of alkyl chains on the torsional angle, crystal packing, and intermolecular interactions such as π-π stacking. Chapter 3 reports the synthesis of novel diketopyrrolopyrrole-diketopyrrolopyrrole (DPPDPP) based conjugated copolymers and their application in high mobility organic field-effect transistors. Effect of insulating alkyl chains on polymer thin film morphology, lamellar packing and π-π stacking interactions have been studied in detail. Investigation of OFET performance of these DPP-DPP copolymers with branched alkyl chains (N-CS2DPP-ODEH) resulted in low charge carrier mobilities as compared to the polymers (N-CS2DPP-ODHE) with linear alkyl chains. Polymer with triethylene glycol side chains (N-CS2DPP-ODTEG) exhibited a high field-effect electron mobility value of ~3 cm2V-1s-1 with a very low threshold voltage of ~2 V. Chapter 4 investigates the effect of torsional angle on the intermolecular interactions and charge transport properties of diketopyrrolopyrrole (DPP) based polymers (PPDPP-OD-HE and PPDPP-OD-TEG). Grazing incidence x-ray diffraction studies shows the different orientation of the polymer crystallites and lamellar packing involved in polymer thin films. Investigation of OFETs evidenced the effect of torsional angle on the charge transport properties where the polymer with higher torsional angle PPDPP-OD-TEG resulted in high threshold voltage with less charge carrier mobility compared to the polymer with lower torsional angle (N-CS2DPP-OD-TEG). Chapter 5 investigates the effect of photoactive material morphology on the solar cell device performance, and charge transfer kinetics by adding high boiling point processing additives. DPP based donor-acceptor (D-A) type low band gap polymers (PTDPPQ and PPDPPQ) have been synthesized and employed in bulk-heterojunction (BHJ) solar cells with the acceptor PC71BM. Addition of processing additive 1,8-diiodooctane (DIO) resulted in three order improvements in power conversion efficiency (PCE). Chapter 6 describes the design and synthesis of two diketopyrrolopyrrole based copolymers (PPDPP-BBT and PTDPP-BBT) for their application in organic devices such as field-effect transistors and bulk-heterojunction solar cells. Investigation of OFET performance of these DPP based copolymers displayed hole mobilities in the order of 10-3 cm2V-1s-1. The semiconductor-dielectric interface has been characterized by capacitance-voltage, and Raman scattering methods. In summary, the work presented in this thesis describes the synthesis and characterization of diketopyrrolopyrrole based new polymeric semiconductors. Effects of insulating side chains and torsional angle on the charge transport properties of these polymers in OFETs have been investigated. This work also describes the effect of solvent additives on the active layer morphology and BHJ solar cell device performance. The results described here show that these materials have potential application as active components in plastic electronics.

Photo-induced charge transfer which occurs between molecules or different parts of a large molecule is the pivotal process related to performances of organic electronics. In particular, injection of charge carriers into conjugated polymers and dissociation of photo-generated excitons at the heterojunction between a donor and acceptor system are of great importance in determining the luminescence efficiency of organic light emitting diodes (OLEDs) and solar energy conversion efficiency of organic solar cells, respectively. However, the complex nature of organic semiconductors as well as complicated primary processes involved in the functioning of these devices have prevented us from understanding unique characteristics of these processes and thereby engineering better materials for higher performances. In this dissertation, two different types of photo-induced (or -related) charge transfer processes occurring in organic semiconductors were investigated by using single molecule spectroscopy (SMS) techniques to unravel the complexities of these processes. The carefully designed functioning capacitor-like model devices similar to OLEDs and photovoltaic cells were fabricated where isolated single nanoparticles were introduced as an active medium to mitigate the complexities of these materials. We observed that injection of positively charged carriers (holes) into poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) single nanoparticles from the carbazole hole transport layer does not occur in the absence of light. We denoted the observed hole injection in aid of light as the light-induced hole transfer mechanism (LIHT). It was revealed that the charging dynamics are highly consistent with a cooperative charging effect. In addition, the LIHT was proposed as the possible source for the formation of deep trapped hole in organic devices. Local exciton dissociation yields across a nanostructured domain between poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) single nanoparticles and either poly(9,9- dioctylfluorene - co - bis-N,N- (4 -butylphenyl)-bis-N,N-phenyl-1,4-phenylene diamine) (PFB) or poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) film in model photovoltaic devices was also investigated. A wide distribution of exciton dissociation yields was observed from each nanodomain due to the device geometry. The observed hysteresis in fluorescence voltage curve was ascribed to accumulated charges following charge separations. The dynamics of charge separation under the applied electric field was described in more detail.
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碩士
淡江大學
化學學系碩士班
97
Recently years, carbazole’s derivatives has been used in photoelectric material generally,and it’s absorption spectrum with solar spectral match. so using in solar cell material will have well absorption coefficient, several alternating polymeric structures have been investigated to carbazole’s derivatives for solar cell applications. This thesis are design the carbazole-based conjugated polymers and uses theoretical and computational methods DFT/B3LYP and basis set 6-31G* to optimize the derivatives structure than uses the TD/B3LYP/6-31G* and ZINDO to calculated the energy level, so we will get three different energy gap value, Eg（DFT）、Eg（TD）and Eg（ZINDO） , than we will get the oligomer n=1~4 energy gap value to find the linear equations, and use the extrapolation method to get the n=∞ energy gap, the Eg（TD）method is most close the experimental value. And we calculated the five oligomer with TD/B3LYP/3-21G to get absorption spectrum, and we will find three kind of oligomer have visible light absorption and two kind of oligomer have near IR absorption. Finally, we use HF/3-21G to calculate excited state structure and TD/B3LYP/3-21G to calculate emission spectrum, and the emission wavelength are between visible light range, so we can speculation the material may be a good photoelectric material. This investigate to provide a good method to design the solar cell material and design three kind of material, For feature it’s will be a good direct to design solar cell material.

碩士
國立交通大學
應用化學研究所
98
In recent years, polymer solar cells (PSCs) have been attracting considerable attention for many advantages, such as low cost, light weight, easy fabrication and their potential application in large area flexible devices. Since the discovery of the photovoltaic effect in bulk heterojunction (BHJ) devices, the considerable publications in PSCs have been reported. PSCs based on the concept of bulk heterojunction (BHJ) configuration where an active layer comprises of a p-type donor (conjugated polymer) and an n-type acceptor (fullerene derivative) materials, represents the most useful strategy to maximize the internal donor-acceptor interface area allowing for efficient charge separation. The goal of this research is to design and synthesize a series of new p-type conjugated polymers to achieve highly efficient BHJ solar cells. Six new cross-conjugated and low bad-gap copolymers have been synthesized and characterized. These of three-component donor-acceptor random copolymers are symbolized as (thiophene donor)m-(thiophene acceptor)n. The PCSTBT series are prepared by Stille coupling polymerization of 2,5-bis(trimethylstannyl)thiophene D1 with 1,4-dibromo-2,5-{bis(4-[N,N-(dioctylamino)styryl])}-benzene) D2 and4,7-dibromo-1,2,3-benzothiadiazole A1, while PCSTDPP series are prepared by Stille coupling polymerization of 2,5-bis(trimethylstannyl)thiophene D1 with1,4-dibromo-2,5-{bis(4-[N,N-(dioctylamino)styryl])}-benzene) D2 and3,6-di(2-bromothien-5-yl)-2,5-dioctylpyrrolo[3,4-c]pyrrole-1,4-dione A2. Thesynthesized copolymers are soluble in common organic solvents and possess good thermal stability. The UV-vis absorption spectra of these copolymers contain an intramolecular charge transfer (ICT) transition band, which lead to an absorption extending into near-infrared region and optical band gaps ranging from 1.36 eV to 1.75 eV. Polymer solar cells of a BHJ were fabricated with the structure of ITO/PEDOT:PSS/Copolymer:PCBM(1:2, w/w)/Ca/Al. The PCE were 0.10 % (PCSTBT25), 0.18 % (PCSTBT50), 0.32 % (PCSTBT75), 0.37 % (PCSTDPP25), 0.54 % (PCSTDPP50), 0.62 % (PCSTDPP75). The higher PCE for PCSTDPP75 copolymer solar cell is attributed to the low band gap of this copolymer compared to others, which increases the numbers of photogenerated excitons and corresponding photocurrent of device. Although their PCE is still relatively low, further improvement on device performance can be achieved through morphology control by thermal annealing and chemical annealing, and carefully device engineering.

碩士
國立臺灣大學
光電工程學研究所
101
The performance of bulk heterjuction (BHJ) solar cells based on low band-gap conjugated polymers and nickel oxide hole transport layers are studied in this thesis. 　　In the first topic of this thesis, the devices of PCDTBT mixed with PC71BM as active layer materials are investigated. By decreasing the thickness of the active layer, the short circuit current density (Jsc) and power conversion efficiency (PCE) are enhanced. Comparing the devices with calcium, lithium fluoride and bathocuproine (BCP) as cathode buffer layers before the deposition of Al electrodes, Jsc of the devices with LiF and BCP buffer layers is higher and PCE of the devices with BCP buffer layers is the highest. The PCE of the device is 4.19%. To control the morphology of the active layer, 1,6-diiodohexane(DIH) is used as an additive, which results in increased PCE to 4.57%. 　　In the second topic, we investigate the device of P3HT: PC61BM based organic solar cells using nickel oxide (NiOx) as the hole transport layers. Via x-ray and ultraviolet photoemission spectroscopy (UPS and XPS), the effects of post-treatment applied to NiOx is investigated. UV Ozone treatment on NiOx results in more metal cation vacancies which contribute to hole transport efficiency. The work function then increases from 4.8 eV to 5.1 eV. The device with ten minutes UV Ozone treatment of the NiOx has maximum fill factor (FF) and PCE. The devices with PEDOT:PSS and the devices with NiOx have similar PCE and Voc , but the former has higher FF and slightly lower Jsc. Additionally, the stability of the devices with NiOx is better than the devices with PEDOT:PSS. 　　In the third topic, we study the device of PBDTTT-C-T: PC71BM as the active layer materials. To achieve the optimized PCE, the active layer parameters such as thickness and concentration are tuned, resulting in the best PCE of 6.10%. Due to the broadened absorption wavelength range and deeper highest occupied molecular orbital (HOMO) of PBDTTT-C-T in comparison with P3HT, Jsc and Voc are higher of the device with PBDTTT-C-T. Then, the NiOx layer is used to replace PEDOT:PSS as the hole transport layer. Since longer UV Ozone treatment time reduces transmission of NiOx, the device with two minutes UV Ozone treatment of NiOx exhibit the optimal PCE of 5.37%. Although PCE of the NiOx device is not as good as that of the PEDOT:PSS device, the stability of the devices with NiOx is much better.

博士
國立交通大學
材料科學與工程學系所
103
Solution-processed organic solar cells (OSCs) prepared through roll-to-roll or inject printing and used within inexpensive, lightweight, flexible devices are being considered as next-generation energy sources. Bulk heterojunctions (BHJ), in which a conjugated polymer (molecule) as a p-type material is blended with a fullerene derivative (e.g., PC61BM) as an n-type material, are the most successful active layer structures for OSCs. In this system, the morphology of BHJ layer play an important role for the high efficient OSCs due to it controls the efficiency of photon-to-current. At early stage, the design and synthesis of novel conjugated polymers and molecules mainly focused on tuning electronic properties, including bang-gaps and energy levels. However, other physical properties, such as solubility, miscibility, and crystallinity, are also important for OSCs, because they could affect the morphology of BHJ layer and the processed condition; therefore, the structure-property relationships of those conjugated materials are worth to be studied. In this thesis, we aimed the investigation at the effects of conjugated-backbone frameworks and alky-chain architectures on molecular stacking characteristics and corresponding processing conditions of devices. In the first part, we insert an extra 4-alkyl thiophene unit as conjugated spacer between benzotrithiophene (BTT) and benzothiadiazole(BT) to synthesize new donor-acceptor conjugated polymer, PBTT4BT. We found this polymer exhibited semi-crystalline characteristic, while the original polymer, PBTTBT, is amorphous. When we used this polymer in bulk heterojunction photovoltaic device applications, the device of PBTT4BT/PC61BM showed an efficiency of 5.6 % which is higher than the device of PBTTBT/PC61BM. On the other hand, we also use benzooxadiazole (BO) to synthesize another polymer, PTT4BO, which has a configuration of PBTT4BT but lower HOMO level. Because PBTT4BO exhibited unsatisfactory solubility limiting the molecular weight, we changed the alkyl-chain bulk on BTT unit to get two high molecular weight polymers, PBTT4BO-C13C11 and PBTT4BO-C13C8. The bulk of the alkyl side chains of these polymers impacted their solubility and molecular interactions, as well as their absorptions properties, crystallinities, and BHJ morphologies. The best efficiency was obtained from the device containing annealed PBTT4BO-C13C8 and PC71BM (w:w/1:2) active layer that had been maintained at 150 °C for 15 min with a power conversion efficiency of 6.2%. Then for the second part, we studied structure-property relationship of small molecules with a configuration of acceptor-donor-acceptor. At first, we synthesized three new small molecules－ TB3t-BT, TB3t-BTT, and TB3t-BDT－ that feature different central cores, including bithiophene, benzotrithiophene, and benzodithiophene units, respectively. The molecular structures of these cores significantly affected the melting and crystallization behaviors as well as formation of crystalline domains in blend films with PC61BM, which leads different efficiencies and processing conditions. Then we further synthesized three new molecules based on the structure of TB3T-BT by attaching different lengths of alkyl chains on central bithiophene unit. Those four molecules displayed two diffraction peaks of the (100) plane in their GIWAXS patterns, indicating polymorphism. Interestingly, the relative intensity of these two peaks changed when we modified the length of the central side chain, suggesting that it also affected the preferred stacking of the small molecules. In addition, the crystallinity within BHJ layer was also affected by side-chain arrangement, the molecules with identical molecules show comparatively better crystalline characteristic resulting higher performance.

博士
國立交通大學
材料科學與工程學系
99
The prime aim of this review is to bring together the areas of narrow band-gap conjugated polymers, dyes, and the supramolecular self assemblies of both dyes and polymers for the applications of organic solar cells. In the first chapter, a brief introduction of evolution of different types of solar cells has been given and also surveyed the literatures for the different structures of conjugated systems which can be efficient for the applications of organic solar cells. In the Second chapter two series of novel symmetrical acceptor-donor-acceptor organic sensitizers (M1-M3 and M4-M6) containing 3,6- and 2,7-functionalized carbazole (donor) cores, respectively, connected with two anchoring cyanoacrylic acid (acceptor) termini via different numbers (2 or 3) of conjugated thienyl linkers (w or w/o hexyl side-chains), were designed and synthesized. The effects of the molecular planarity originated from the central electron-donating 3,6- and 2,7-functionalized carbazole cores on device performance were studied. A structure-based density functional theory (DFT) calculation confirmed the efficiencies of the dyes being related to the coplanarity of the carbazole cores with respect to the linked thiophene units. Molecular orbital analyses reflected the characterstics of the carbazole-based highest occupied molecular orbitals (HOMOs) and acid-based lowest unoccupied molecular orbitals (LUMOs) along with the bridged thiophene units were essential for strong conjugations across the donor-acceptor groups, while time-dependent density functional theory (TDDFT) calculations allowed the assignment of HOMO–LUMO transitions (>90%) of the low energy bands in these new systems. Among these dyes, the best dye sensitized solar cell (DSSC) performance was obtained from the DSSC device containing M1, bearing 3,6-functionalized carbazole center linked by two symmetrical bithiophene groups, with an overall power conversion efficiency (讯) value of 4.82%, an open circuit voltage (Voc) of 0.61 V, a short circuit photocurrent density (Jsc) of 12.66 mA/cm2, and a fill factor (FF) of 0.62 under standard AM 1.5 sunlight with a maximum incident photon to current conversion efficiency (IPCE) of 68%. Furthermore, it is very impressive to observe the IPCE and Jsc values of the DSSCs in TiO2-based thin films (3 μm) containing M1 and M5 dyes were higher than those of the DSSC containing ruthenium-based N719 sensitizer. In the third chapter four novel symmetrical organic dyes (S1-S4) configured with acceptor-donor-acceptor (A-D-A) structures containing electron donating fluorene (S1 and S2) and N-alkyl dithieno[3,2-b:2',3'-d]pyrrole (DTP) (S3 and S4) cores terminated with two anchoring cyanoacrylic acids (as electron-acceptors) were synthesized and applied to dye-sensitized solar cells (DSSCs). The DSSC device based on S2 dye showed the best photovoltaic performance among S1-S4 dyes: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 76%, a short circuit current (Jsc) of 12.27 mA/cm2, an open circuit voltage (Voc) of 0.61 V, a fill factor (FF) of 0.63, and an overall power conversion efficiency (η) of 4.73%. Besides, the utilization of chenodoxycholic acid (CDCA) as a co-adsorbent in the DSSC device based on S3 dye showed a significant improvement in its η value (from 3.70% to 4.31%), which is attributed to the suppression of dye aggregation on TiO2 surface and thus to increase the Jsc value eventually. In the fourth chapter a series of novel low-bandgap triphenylamine-based conjugated polymers (PCAZCN, PPTZCN, and PDTPCN) consisting of different electron-rich donor main chains (N-alkyl-2,7-carbazole, phenothiazine, and cyclopentadithinopyrol, respectively) as well as cyano- and dicyano-vinyl electron-acceptor pendants were synthesized and developed for polymer solar cell (PSC) applications. The polymers covered broad absorption spectra of 400-800 nm with narrow optical bandgaps ranging 1.66-1.72 eV. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the polymers measured by cyclic voltommetry (CV) were found in the range of -5.12 to -5.32V and -3.45 to -3.55 eV, respectively. Under 100 mW/cm2 of AM 1.5 white-light illumination, bulk heterojunction (BHJ) photovoltaic devices comprising of an active layer of electron donor polymers (PCAZCN, PPTZCN, and PDTPCN) blended with electron-acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) or [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) in different weight ratios were investigated. The photovoltaic device containing donor PCAZCN and acceptor PC71BM in 1:2 weight ratio showed the highest power conversion efficiency (PCE) of 1.28 %, with Voc = 0.81 V, Jsc = 4.93 mA/cm2, and FF = 32.1%. In the fifth chapter a series of novel hydrogen-bonded (H-bonded) cross-linking polymers were generated by complexing various proton-donor (H-donor) solar cell dyes containing 3,6- and 2,7-functionalized electron-donating carbazole cores bearing symmetrical thiophene linkers and cyanoacrylic acid termini with a proton-acceptor (H-acceptor) side-chain homopolymer carrying pyridyl pendants (with 1/2 molar ratio of H-donor/H-acceptor). The supramolecular H-bonded structures between H-donor dyes and the H-acceptor side-chain polymer were confirmed by FTIR measurements. The effects of the supramolecular architecture on optical, electrochemical, and organic photovoltaic (OPV) properties were investigated. From DFT (density functional theory) calculations, the optimized geometries of organic dyes reflected that the carbazole cores of H-donor dyes were coplanar with the conjugated thiophenes and cyanoacrylic acids, which is essential for strong conjugations across the donor-acceptor units in D1-D4 dyes. Under 100 mW/cm2 of AM 1.5 white-light illumination, bulkheterojunction (BHJ) OPV cell devices containing an active layer of H-bonded polymers (PDFTP/D1-D4) as an electron donor blended with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as an electron acceptor in a weight ratio of 1:1 were explored. From the preliminary investigations, the OPV device containing 1:1 weight ratio of H-bonded polymer PDFTP/D2 and PCBM showed the best power conversion efficiency (PCE) value of 0.31% with a short-circuit current (Jsc) of 1.9 mA/cm2, an open-circuit voltage (Voc) of 0.55 V, and a fill factor (FF) of 29%, which has a higher PCE value than the corresponding H-donor D2 dye (PCE = 0.15%) or H-acceptor PDFTP homopolymer (PCE = 0.02%) blended with PCBM in 1:1 weight ratio.

碩士
國立交通大學
應用化學系碩博士班
106
In this study, we successfully synthesized two D-A wide-bandgap conjugated polymers, PNTzBDT1 and PNTzBDT2, based on the naphtho[1,2-d:5,6-d']bis([1,2,3]triazole (NTz) and benzo[1,2-b:4,5-b']dithiophene (BDT) as the monomers, both of these two polymers have the optical bandgap are 1.9 eV, and are applied in the non-fullerene polymer solar cells. By introducing the triazole unit, we can place the side chain on the nitrogen atom rather than the thiophene in the main chain, hence the co-planarity of the π-conjugated system will be increased. We use the alkyl side-chain with various bulkiness on the BDT and NTz monomers respectively, however, the total carbon number is the same for the two polymers, to see how the different side-chain on the polymers affect the solubility, physical, chemical properties and the molecular packing in the thin-film solid state. According to the computational calculations, PNTzBDT1 has the better co-planarity, therefore, it has the better inter-chain packing, stronger π-π interaction and poorer solubility, whereas PNTzBDT2 shows the curved backbone, results in weaker inter-chain interaction and better solubility. The UV-Vis absorption of the two polymers and PC71BM are partially overlapping, consequently, we choose the non-fullerene acceptor, ITIC, as the n-type material to make up the absorption in long wavelength region. Bulk heterojunction solar devices were fabricated with inverted architecture (ITO/ZnO/Active layer/Ag/MoO3). The device using the PNTzBDT2:ITIC shows a PCE of 5.26% with a Voc of 0.88 V, a FF of 46.8%, and a Jsc of 12.75 mA/cm2. Under similar conditions, the device using the PNTzBDT1:ITIC presents a PCE of 7.37% with a high Voc of 0.94 V, a FF of 55.8, and a Jsc of 14.04 mA/cm2.

碩士
國立交通大學
應用化學系碩博士班
105
Selenophene has several advantages such as high polarizability and high quinoidal population which endow many selenophene-based materials with narrower optical bandgap, enhance light-harvesting ability and higher crystallinity. These beneficial properties lead to the improved charge carrier mobiliies in transistor devices or higher photocurrents in OPV devices. The traditional method to synthesize 3-alkyl selenophene is quite complicated and costly. We successfully design an efficient way to simplify the synthesis of selenophene. We utilize selenophene to synthesize three donor-acceptor copolymers consisting of 5,6-difluorobenzo[2,1,3]thiadiazole (FBT) and selenophene called PFBT2Th2Se, PFBT2Se2Th and PFBT4Se, respectively. Selenophene has higher intramolecular charge transfer ability with FBT than thiophene. Therefore, the polymers containing selenophene display more red-shifted absorption. The selenophene-containing polymers also show temperature-dependent absorption spectrum, indicating that the incorporation of selenophene does not affect the crystalline behavior of the polymers. Furthermore, the results from differential scanning calorimeter (DSC) confirm that these three polymers have crystalline behavior since it shows the obvious melting point upon heating and the clear crystallization point upon cooling. The combination of these characteristics enhances the charge transport efficiency. Hence, the devices which utilize these selenophene-containing polymers can obtain impressive current density (>20 mA/cm2). To gain a deeper insight into the nanoscale morphology and orientation of the photoactive layers, the grazing-incidence wide-angle X-ray diffraction (GIWAXD) was employed. The results suggest that the three polymers blended with PC71BM adopt face-on orientation which is beneficial for charge carrier transport in the vertical direction in the active layer. Organic photovoltaic devices are fabricared with inverted atchitecture (ITO/ZnO/Active layer/MoO3/Ag). The device using PFBT2Th2Se:PC71BM shows a PCE of 8.68 % with a Voc of 0.68 V, an FF of 69.1 %, and a high Jsc of 18.46 mA/cm2. Under similar conditions, the device using the PFBT2Se2Th:PC71BM blend presents a PCE of 9.02% with a Voc of 0.66 V, an FF of 65.0 %, and an impressive Jsc of 21.02 mA/cm2. Furthermore, the device with PFBT4Se displays a PCE of 8.92 % with a Voc of 0.62 V, FF of 63.6 %, and a superior Jsc of 22.63 mA/cm2 which represents one of the highest current densities from PSCs reported in the literature.

博士
國立臺灣大學
化學研究所
106
This thesis can be divided into 2 parts. The first was concentrated on designing and synthesizing donor materials for the organic photovoltaics (OPVs). The second part was focused on developing of electron transporting materials for the perovskite solar cells (PVSCs). In the first part, we have synthesized and characterized a series of diketopyrrolopyrrole (DPP)-oligothiophene copolymers, of which the number of regioregular oligothiophene ring (2T, 3T and 4T) and the arrangement of the alkyl side-chain on regioirregular quarterthiophene (4T0, 4T1 and 4T2) are variable. The side chains with regioregular lead to more planar copolymer backbones and higher short circuit current (JSC), but backbone torsion (due to regioirregular side chains) generates greater open-circuit voltages (VOC) for DPP-oligothiophene copolymers. The increasing thiophene ring progressively raises HOMO energy level of copolymers but marginally affects their band gaps. Additionally, the HOMO energy level was found declined significantly with side-chain regioirregularity, because of reducing length of π-conjugation. The HDDPP4T0 exhibits the strongest absorption, extensive network structure, and high hole mobility (µh = 6.04 × 10-4 cm2 V-1 s-1). These characteristics contribute to the exceptional high JSC of 18.96 mA cm-2 for OPV with PCE = 6.12%. However, the HDDPP4T1 having an optimal combination of π-conjugation and energy level affords the second highest VOC (0.73 V) and the third highest JSC (16.89 mA cm-2), resulting the best PCE of 7.51 % among all. X-ray scattering, transmission electron microscopy, atomic force microscopy, and space-charge-limited-current (SCLC) easurements reveal that the solvent additive of diphenylether (DPE) enables PC71BM-blended copolymers thin film in crystallinic fibril with enhanced hole mobility. In the second part, we have developed and demonstrated three solution processable perylene diimides, i.e., X-PDI, X = H, F, or Br, as nonfullerene electron accepting and electron transporting materials in inverted PVSCs. Whereas H-PDI or F-PDI performs unsatisfactorily, our best PVSC is based on Br-PDI exhibiting PCE of 3.23%, which is just a bit shy of 4.13% of fullerene (PC61BM) PVSCs. Through a series of physical, spectroscopic, and microscopic studies, we have understood that the low solubility of F-PDI is a major factor causing the poor quality of the thin film, rendering virtually no photovoltaic effect for F-PDI. Although the solubility of H-PDI is better than F-PDI, the inferior electron mobility and conductivity make H-PDI PVSCs have relatively worse performance. Having the highest solubility, electron mobility, and conductivity among X-PDI, Br-PDI based PVSCs are almost as efficient as PC61BM based PVSCs. Within the ZnO NP as a CBL in the PVSCs, the PCEs of PVSCs based on X-PDI or PC61BM are significantly improved to 7.78%, 10.50%, and 11.07%, respectively.We infer that the CBL of ZnO NP has the function of interspacelling on the defect of X-PDI or PC61BM thin film, reducing the direct contact of Ag cathode to the perovskite material. Due to the strong molecular interaction, F-PDI aggregates significantly in thin film, creating too many and too large defects to be remedied or improved with or without CBL of ZnO NP. Very poor electron mobility and conductivity of F-PDI are two other factors devastating its PVSCs. Through this study, we have demonstrated that the simple mono-bromine substituted perylene diimide (Br-PDI), is solution processable and has potential for use as a non-fullerene electron accepting and electron transporting material in inverted PVSCs.

The present thesis is focused on rational design and synthesis of π-conjugated donoracceptor-donor (D-A-D) type oligomers and D-A type copolymers. Thesis is organized in seven chapters, apart from introduction remaining six chapters are grouped into two parts (A and B). Part A deals with Chapters 2, 3, 4 and Part B contains chapters 5, 6 and 7. A brief discussion on the content of individual chapters is provided below. Chapter 1 discusses the introduction to organic solar cell with operating principles and effect of spinodal decomposition on stability of the devices is presented. The status and literature related to the improvement of life time of the organic solar cells by self-assembly approach has been explored. In addition, design and synthesis of the fluorine substituted π-conjugated organic semiconductors for n-type OFETs and OLED has been discussed. Part A This part of the thesis attempt to address some of the challenges listed below (1) Investigation of miscibility of binary components in bulk heterojunction solar cells through H-bonding approach. (2) Synthesis of new low band gap molecular semiconductors having H-bonding sites. (3) Fabrication of bulk heterojunction solar cell devices using these new molecules and exploring the photovoltaics performance. Chapter 2, donor-acceptor-donor (D-A-D) concept has been employed to design low band gap oligomers named as TTB. Barbiturate functional group has been utilized to explore the concepts of supramolecular chemistry. It is shown that, TTB molecule self-organizes via intermolecular H-bonding between barbituric acid units. Interactions between the oligothiophene subunits were also found to be important, affording nanoribbons that were observed by atomic force and transmission electron microscopy. The applicability of TTB for organic electronic applications was investigated by fabricating organic field-effect transistors (OFETs) and organic photovoltaic device. The crystalline nanoribbons were beneficial in understanding the phase morphology of PCBM and TTB blend. Chapter 3, the self-assemble property of TTB was disrupted by the substitution of methyl group on the nitrogen of the barbituric acid moiety. The optical and electrochemical properties of the new derivative have been investigated by UV-Visible spectroscopy, photoluminescence spectroscopy and cyclic voltammetry. Further investigations on the effect of self-assembly on organic solar cells were carried out by fabricating BHJ and OFET. The results proved that the self-assembly within the donor moieties led to complete phase separation between the donor and acceptor which had an adverse effect on the photovoltaic performance. Chapter 4, the conjugation of TTB was extended by the synthesis of two new copolymers by polymerizing with two oliogothiophene (terthiophene and benzobithiophene) derivatives with different donating strength. The investigation of photophysical and electrochemical properties of copolymers were studied by varying the donating strength. As we increase the donating strength of oligothiophenes, the intramolecular charge transfer band of DA copolymers was red shifted. Further, density functional theory (DFT) calculation of these materials was carried out to get insight into their photophysical properties. Part B This part of the thesis attempt to address some of the challenges listed below (1) Investigation of fluorine substituted organic semiconductos like 2,2’ bithiazole and pheanthroimidazole. (2) Synthesis of pentafluoro phenyl appended derivatives of 2,2’ bithiazole and pheanthroimidazole. (3) Fabrication of OFETs and OLEDs using these new molecules and elucidated the device performance with molecular structure. Chapter 5, pentafluorophenyl appended 2,2’-bithiazole derivatives were synthesized. The single crystal x-ray diffraction studies shows the unusual strong type-II F•••F interactions within the distance of 2.668 Å, at an angle of 89.14° and 174.15°. It also shows the usual type-I F•••F interaction within the distance of 2.825Å, at an angle of 137.38° and 135.93°. Upon bromination type-II Br•••Br interaction was observed and the packing was further stabilized by S•••Br interactions. The conjugation was further extended with different aromatic and heteroaromatic substituents and synthesized the star shaped structure. The band gap as well as the electronic energy levels was tuned by substituting various aromatic and heteroaromatic substituents. These star shaped derivatives shows electron mobilities in the order of 10-4 to 10-3cm2/Vs. Chapter 6, Novel D-A copolymers were synthesized by Stille condensation of electron acceptor fluorinated phenanthroimidazole with electron donors like terthiophene and benzobithiophene. Prior to that insoluble pentafluoro phenyl phenanthroimidazole was Nalkylated in presence of DMF which concurrently resulted in C-F activation of the pentafluoro phenyl moiety. As we increase the donor strength from benzobithiophene to terthiophene the absorbance spectra was red shifted from 446 nm to 482 nm in solution and 455 nm to 484 nm in solid state. The band gap of these copolymers was found to be 2.4 eV for PIBDT and 2.2 eV for PIDHTT from the absorbance spectra. The photoluminescence data shows that these materials are promising for the yellow colour as well as orange colour displays, of narrow wavelength range (FWHM 40 nm for PIBDT and 35 nm for PIDHTT), which can be achieved just by the manipulation of donor moieties in the copolymers. The preliminary electroluminiscence data shows high brightness of 888cd/m2 (orange luminescence) for PIDHTT and 410cd/m2 (yellow luminescence) for PIBDT. Chapter 7, Acenaphtho[1,2-b]quinoxaline based donor–acceptor type low band gap conjugated copolymers were synthesized by Stille coupling reaction with the corresponding oligothiophene derivatives. The optical properties of the copolymers were characterized by ultraviolet-visible spectrometry while the electrochemical properties were determined by cyclic voltammetry. The band gap of these polymers was found to be in the range of 1.8-2.0 eV as calculated from the optical absorption band edge. The intense charge transfer band in absorption spectra shows the significant effect of acceptor in the copolymers. X-ray diffraction measurements show weak π–π stacking interactions between the polymer chains. The OFET devices fabricated using these co-polymers showed dominant p-channel transistor behavior with the highest mobility of 1×10-3cm2/Vs.

All-polymer solar cells (APSC) are a class of organic solar cells in which hole and electron transporting phases are made of conjugated polymers. Unlike polymer/fullerene solar cell, photoactive material of APSC can be designed to have hole and electron transporting polymers with complementary absorption range and proper frontier energy level offset. However, the highest reported PCE of APSC is 5 times less than that of polymer/fullerene solar cell. The low PCE of APSC is mainly due to: i) low charge separation efficiency; and ii) lack of optimal morphology to facilitate charge transfer and transport; and iii) lack of control over the exciton and charge transport in each phase. My research work is focused towards addressing these issues. The charge separation efficiency of APSC can be enhanced by designing novel electron transporting polymers with: i) broad absorption range; ii) high electron mobility; and iii) high dielectric constant. In addition to with the above parameters chemical and electronic structure of the repeating unit of conjugated polymer also plays a role in charge separation efficiency. So far only three classes of electron transporting polymers, CN substituted PPV, 2,1,3-benzothiadiazole derived polymers and rylene diimide derived polymers, are used in APSC. Thus to enhance the charge separation efficiency new classes of electron transporting polymers with the above characteristics need to be synthesized. I have developed a new straightforward synthetic strategy to rapidly generate new classes of electron transporting polymers with different chemical and electronic structure, broad absorption range, and high electron mobility from readily available electron deficient monomers. In APSCs due to low entropy of mixing, polymers tend to micro-phase segregate rather than forming the more useful nano-phase segregation. Optimizing the polymer blend morphology to obtain nano-phase segregation is specific to the system under study, time consuming, and not trivial. Thus to avoid micro-phase segregation, nanoparticles of hole and electron transporters are synthesized and blended. But the PCE of nanoparticle blends are far less than those of polymer blends. This is mainly due to the: i) lack of optimal assembly of nanoparticles to facilitate charge transfer and transport processes; and ii) lack of control over the exciton and charge transport properties within the nanoparticles. Polymer packing within the nanoparticle controls the optoelectronic and charge transport properties of the nanoparticle. In this work I have shown that the solvent used to synthesize nanoparticles plays a crucial role in determining the assembly of polymer chains inside the nanoparticle there by affecting its exciton and charge transport processes. To obtain the optimal morphology for better charge transfer and transport, we have also synthesized nanoparticles of different radius with surfactants of opposite charge. We propose that depending on the radius and/or Coulombic interactions these nanoparticles can be assembled into mineral structure-types that are useful for photovoltaic devices.