Academic literature on the topic 'BHJ solar cell'

Semitransparent bulk-heterojunction (BHJ) solar cells have attracted a strong attention due to the possible use in new photovoltaic applications. However, semitransparent BHJ solar cells on flexible substrates have not yet been developed. In this work, flexible BHJ solar cells were fabricated on an ITO/PET substrate using an inverted PET/ITO/PFN/PTB7:PC71BM/MoO3/Au device structure. The power conversion efficiency (PCE) of the device was 3.4 %. Fabrication of semitransparent solar cells was further demonstrated utilizing a MoO3/Au/MoO3 transparent anode. The semitransparent solar cell showed bifacial energy generation when illuminated from both front and backside. The PCEs with illumination from the ITO or Au/MoO3 side were 2.7 % and 2.1 %, respectively. These results showed that a semitransparent PTB7:PC71BM solar cell was successfully fabricated on flexible PET substrates.

The energy scenario today is focused on the development and usage of solar cells, especially in the paradigm of clean energy. To readily create electron and hole pairs, solar cells utilize either photoactive or photosensitive components. A bulk heterojunction (BHJ) is a nanolayer consisting of donor and acceptor components with a large interpenetrated acceptor and donor contact area. In this context, a mix of P3HT and PCBM offers novelty for its use as an acceptor as well as a donor. In the work presented here, we address the mechanism of modelling and characterization of a BHJ-based polymer solar cell. Here, a new design of BHJ polymer solar cells have been designed, modelled, using Silvaco TCAD in the Organic Solar module, and matched with an already assembled device having similar features. Using this model, we have been able to estimate key parameters for the modelled devices, such as the short-circuit current density, open-circuit voltage, and fill factor with less than 0.25 error index compared to the fabricated counterpart, paving the way for fabless polymer solar cell design and optimization.

We applied an effective medium model for a computational study and investigated a recombination mechanism in a P3HT:PCBM bulk heterojunction (BHJ) organic solar cells where the main assumption is the p-n nanostructure is treated as one single effective semiconductor layer, and parameters in this configuration are fed into a standard solar cell device simulator, called a Solar Cell Capacitance Simulator (SCAPS). Using SCAPS, the electrical performances of organic solar cells and the intensity-dependent current density -voltage (J-V) were simulated and compared with the actual experimental result. The results show that they are in good agreement with each other and monomolecular recombination mechanism is the dominant mechanism in the BHJ organic solar cells.

Recently, emerging third-generation photovoltaic technologies have shown rapid progress in device performance; the power conversion efficiencies (PCEs) of organic bulk heterojunction (BHJ) and perovskite solar cells (PSCs) are now surpassing 19% and 25%, respectively. Despite this dramatic enhancement, their efficiencies are theoretically limited based on the detailed balance model which accounts for inevitable loss mechanisms under operational conditions. Integrated solar cells, formed by monolithically integrating two photoactive layers of perovskite and BHJ with complementary absorption, provide a promising platform for further improvement in solar cell efficiency. In perovskite/BHJ integrated solar cells (POISCs), high bandgap perovskite offers high open-circuit voltage with minimal losses while low bandgap organic BHJ extends absorption bandwidth by covering the near-infrared region, resulting in additional photocurrent gain. Different from conventional tandem solar cells, integrated solar cells contain merged photoactive layers without the need for complicated recombination layers, which greatly simplifies fabrication processes. In this review, we summarize the recent progress in POISCs, including operational mechanism and structural development, and remaining challenges on the road toward efficient devices.

Side chain ester substitution on donor–acceptor based conjugated polymers used as solar harvesters in a bulk-heterojunction (BHJ) polymer solar cell (PSC) can improve harvesting properties, phase separation in the active layer and PSC performance.

F-Substituted oligothiophenes were designed and used as nonfullerene acceptors in BHJ solar cells. With low-bandgap polymer donors, the solar cell devices reach PCEs of up to 4.5% and open-circuit voltages >1 V.

In this work, we demonstrate that modifying the I/Br ratio in perovskite composition, the OPV layer in integrated perovskite/OPV (BHJ) system shows different functionality–hole transporting layer or independent solar cell.

Harvesting the unlimited and renewable energy from sunlight to produce electricity is one of the major scientific and technological challenges of the 21st century. Among the available techniques, photovoltaic solar cells (PVCs) are very attractive because they can convert solar energy directly into electricity in a reasonable and economic appealing efficiency. The development of PVCs is therefore an attractive alternative to address global environmental issues. However, the current high cost for the devices based on inorganic semiconductors has limited their widespread application. Organic solar cells offer a compelling option for tomorrow’s PV devices, since they can be easily prepared using low-cost and efficient roll-to-roll manufacturing processes. During the last decade, Organic Photovoltaic (OPV) research has progressed remarkably both in terms of new materials and device performances. Particular interest have been devoted to bulk heterojunction (BHJ) devices in which the active layer consists of a blend of DONOR (p-type semiconductor) and ACCEPTOR (n-type semiconductor) materials. The active layer can be easily deposed through put techniques, facilitating the formation of large area, light weight, and potentially flexible devices. Fullerenes C60, C70 and in particular their soluble derivates (PCBM) are at the moment the most popular ACCEPTORS and only marginal research is devoted to the development of viable substitutes. On the other hand, the research has been focused on conjugated polymers, as DONOR material, due to their tunable properties by a structural design and the possibility to produce them at low costs. Over the past decade, research has focused on regioregular poly(3-hexylthiophene) (P3HT) as the standard electron-donating material in polymer BHJ solar cells, with important progresses having been made in understanding the device science and the associated improvements in device efficiency. However, P3HT is not the ideal polymer as it has a relatively large band gap (1.85 eV, and this means that it is not able to harvest the maximum of exploitable solar radiation) and its high-lying highest occupied molecular orbital (HOMO) (-5.1 eV) limits the open circuit voltage (Voc) of P3HT/PC61BM devices to 0.6 V, consequently limiting the efficiency to about 5%. To overcome these limitations, low band gap materials with broad absorption spectra, to enhance sunlight harvest for higher short circuit current (Jsc); appropriately lower HOMO energy levels, to maximize the open circuit voltage (Voc); higher hole mobilities, for higher Jsc; and higher fill factor (FF), have been proven to be an efficient strategy to improve device performance. Typically, a low band gap polymer is designed, via donor-acceptor (D-A) approach, by incorporating both electron-rich and electron-deficient moieties in the same conjugated backbone. Among a wide variety of donor material, new low band gap polymers based on thiophene, as the donor unit, and iso-DPP (iso-diketopyrrolo-pyrrole) or maleimide, as the acceptor moieties, were designed. These latter electron-withdrawing units combine a low HOMO level and a rigid planar core that permit π-conjugation length and charge transfer into the polymer backbone. The polymers and the molecules obtained by Stille condensations were characterized into the device as DONOR material or third compound to blend with the classical mix P3HT/PCBM. More into the detail, the Chapter 3 reports on the synthesis of a novel electron-deficient derivative, 1,4-dibutyl-3,6-di(thiophene-2-yl)pyrrolo[3,2-b]pyrrole-2,5-dione (iso-DPP). This new building block was copolymerized with bistannanes of thiophene and bithiophene by Stille polycondensation, affording the corresponding polymers (PDPPT and PDPPTT, respectively). These compounds exhibit small energy band gaps combined with low-lying HOMO energy levels. Energy band gaps of PPDPT and PPDPTT, calculated from absorption spectra, are 1.63 and 1.73 eV, respectively. The HOMO and LUMO energy levels of PDPPT and PDPPTT are -5.12, -3.50, -5.09 and -3.50 eV respectively, as determined by cyclic voltammetry. The power conversion efficiency of PDPPT:PC60BM-based photovoltaic cells illuminated by AM 1.5G was 1.24%, without optimization of materials, significantly higher than for PDPPTT:PC60BM, 0.33%. The results demonstrate that iso-DPP based polymers are promising materials for bulk heterojunction solar cell applications. A series of D-A polymers and oligomers based on N-alkyl-maleimide has been synthesized by a simple and efficient route explained in Chapter 4. The obtained low band-gap materials were applied into polymeric photovoltaic cells, to improve their efficiency by tuning their electronic properties. The introduction of small quantities (< 20% w/w) of polymers or oligomers containing N-alkyl-maleimide within active layer of P3HT/ PC61BM blends allowed to dramatically increase the efficiencies of BHJ solar cells (up to 80% of increase). This beneficial effect is attributed to improved charge photogeneration and transport. Poor photovoltaic results were obtained if the maleimide based polymer was employed alone as DONOR material, blended with PC61BM. In order to obtain good results in terms of device performances, not only a good chemical design of the DONOR polymer must be achieved, but also other parameters at the molecular and supramolecular levels should be carefully controlled. The full potential of any conjugated polymer for solar cells can only be realized with an optimized morphology. For this purpose the synthesis of random and diblock copolymers of poly(3-alkylthiophene)s bearing polar substituents was successfully developed by GRIM polymerization and the details are reported in Chapter 5. 3-Hexyl-thiophene was successfully copolymerised with a new derivative, 3-functionalised-thiophene (propyl 5-(2-(thiophen-3-yl)ethoxy) pentanoate), bearing an ester function. Under optimized conditions, this ester proved to be fully compatible with the Grignard metathesis polymerization. Saponification of the copolymer esters provided the corresponding polyacids. Photovoltaic properties of copolymers were investigated in bulk heterojunction devices with PC61BM as acceptor. Among all the amphiphilic copolymers, P3HT-b-P3AcidHT showed the best performance with a PCE of 4.2%, an open-circuit voltage (Voc) of 0.60 V, a short-circuit current density (Jsc) of 13.0 mAcm-2, and a fill factor (FF) of 0.60. All conjugated D-A molecule and polymers were characterized by chemical investigation and their optical, electrochemical, morphological and photovoltaic properties were investigated.
Convertir l'énergie illimitée et renouvelable du soleil pour produire de l'électricité est l'un des plus grands défis scientifiques et technologiques du 21e siècle. Parmi les techniques disponibles, les cellules solaires photovoltaïques (cellules PV) sont très intéressantes car elles peuvent convertir directement l'énergie solaire en électricité avec un rendement assez élevé. Le développement des cellules PV est donc une alternative intéressante pour aborder les problèmes environnementaux mondiaux. Cependant, le coût élevé pour les dispositifs à base de semi-conducteurs inorganiques a limité leur application à grande échelle. Les cellules solaires organiques offrent une option convaincante pour les dispositifs photovoltaïques de demain, car ils peuvent être facilement mis en œuvre à faible coût et bénéficier de procédés de fabrication rouleaux à rouleaux (roll-to-roll) ou feuilles à feuilles (sheet-to-sheet). Au cours de la dernière décennie, la recherche sur le photovoltaïque organique (OPV) a progressé de manière remarquable à la fois en ce qui concerne de nouveaux matériaux et aussi les performances des dispositifs. Un intérêt particulier a été consacré aux composants à hétérojonction en volume (BHJ), dans lesquels la couche active est constituée d'un mélange intime de matériaux : un DONNEUR (semi-conducteur de type p) et un accepteur (semi-conducteur de type n). La couche active peut être facilement déposée par des techniques en voie liquide, et ainsi faciliter la fabrication sur de grandes surfaces, avec un poids léger, et donc sur des substrats potentiellement flexibles. Les fullerènes C60 ou C70 et en particulier leurs dérivés solubles (PCBM) sont pour le moment les ACCEPTEURS les plus populaires, et seulement une recherche marginale est consacrée à la mise au point de matériaux de remplacement viables. La recherche s'est concentrée sur des polymères conjugués, comme matériau de donneur, en raison de leurs propriétés accordables par conception structurale et une potentielle production à faible coût. Au cours de la dernière décennie, les études se sont intéressées au poly (3-hexylthiophène) (P3HT) régio-régulier comme principal matériau donneur d'électrons dans les cellules solaires polymères en volume (BHJ). D'importants progrès ayant été réalisés dans la compréhension des dispositifs améliorant ainsi l'efficacité de ceux ci. Toutefois, le P3HT n'est pas le polymère idéal car il possède une bande interdite relativement large (1,85 eV) et sa plus haute orbitale moléculaire occupée (HOMO) (-5,1 eV) restant trop grande, elle limite la tension de circuit ouvert (Voc) des dispositifs P3HT/PC61BM à 0,6 V. Ceci à pour conséquence de limiter l'efficacité des cellules aux alentours de 5%. Pour résoudre ce problème et augmenter la conversion solaire, une stratégie efficace est d'utiliser des matériaux à faible bande interdite avec des spectres d'absorption larges. Il en résulte une augmentation du courant de court-circuit (Jsc). En choisissant de manière appropriée le niveau HOMO, on peut maximiser la tension en circuit ouvert (Voc). Enfin des mobilités de trous supérieures et une meilleure Jsc engendreront un meilleur facteur de forme (FF). Typiquement, un polymère de faible largeur de bande interdite est réalisé par l'intermédiaire d'une approche donneur-accepteur (D-A), en incorporant les deux fractions celle riche en électrons et celle pauvre en électrons sur le même squelette conjugué. Parmi un large éventail de nouveaux matériaux donneurs à faible bande interdite, des polymères où l'unité du donneur est à base de thiophène ont été fabriqués; ces composés conçus ont comme groupement accepteur : l'iso-DPP (iso-dicétopyrrolopyrrole) ou maléimide. Ces structures électro-attractrices combinent un niveau HOMO bas et un noyau rigide plan qui permet une longueur de conjugaison π et un transfert de charges dans le squelette du polymère. Les polymères et les molécules obtenues par condensation de Stille ont été caractérisés dans des dispositifs comme matériau donneur ou comme additif dans le mélange classique P3HT/PCBM. Il sera détaillé dans le chapitre 3, la synthèse d'un nouveau dérivé déficient en électrons, le 1,4-dibutyl-3,6-di-(thiophène-2-yl)-pyrrolo-[3,2-b]-pyrrole-2,5-dione (iso-DPP). Cette nouvelle brique moléculaire a été co-polymérisée avec des bistannanes de thiophène et des bithiophènes par polycondensation de Stille, pour obtenir les polymères correspondants (respectivement PDPPT et PDPPTT). Ces composés présentent une faible bande d'énergie interdite combinée à des niveaux d'énergie HOMO bas. Les bandes d'énergie interdites de PPDPT et PPDPTT, calculées à partir des spectres d'absorption, sont respectivement de 1,63 et 1,73 eV. Les niveaux HOMO et LUMO déterminés par voltampérométrie cyclique sont de -5,12 et -3,50 eV pour le PDPPT, et de -5,09 et -3,50 eV pour le PDPPTT. L'efficacité, sous éclairement AM 1.5G, des cellules photovoltaïques à base de PDPPT: PC60BM est de 1,24%, sans optimisation des matériaux, nettement plus élevée que pour celle des dispositifs à base de PDPPTT: PC60BM qui est de 0,33%. Les résultats démontrent que les polymères à base d'iso-DPP sont des matériaux prometteurs pour l'utilisation en cellules solaires à hétérojonction en volume. Une série de polymères donneur-accepteur et d'oligomères donneur-accepteur conçs sur des structures à base de N-alkyl-maléimide ont été synthétisés par une voie simple et efficace expliquée dans le chapitre 4. Les matériaux à faible gap obtenus ont été utilisés dans des cellules photovoltaïques polymères, afin d'en améliorer leur efficacité en optimisant leurs propriétés électroniques. L'introduction de petites quantités (<20% en rapport en masse) de polymères ou d'oligomères contenant des N-alkyl-maléimide à l'intérieur des couches actives de mélanges P3HT / PC61BM a permis d'augmenter considérablement l'efficacité de ces cellules solaires à hétérojonction en volume (jusqu'à 80% d'augmentation). Cet effet bénéfique est attribué à une amélioration de la photo-génération des charges et du transport dans la couche. Quand le maléimide est utilisé seul comme matériau donneur mélangé au PC61BM, les résultats sont en revanches mauvais. Afin d'obtenir de bons résultats en performances de dispositifs, il faut non seulement réaliser un bon design chimique du polymère donneur, mais contrôler soigneusement d'autres paramètres au niveau moléculaire et supramoléculaire. Le meilleur potentiel d'un polymère conjugué ne peut être obtenu qu'avec une optimisation maitrisée de la morphologie de celui-ci. A cet effet, la synthèse de copolymères aléatoires et di-bloc à base de poly-(3-alkylthiophène) portant des substituants polaires a été développée avec succès par polymérisation GRIM. Ces détails sont présentés dans le chapitre 5. La co-polymérisation du 3-hexyl-thiophène avec un nouveau dérivé, 3-thiophène-fonctionnalisé (propyl-5-(2-(thiophén-3-yl)-éthoxy)-pentanoate), porteur d'une fonction ester a été réalisée avec succès. Dans des conditions optimales, cet ester s'est avéré être pleinement compatible avec la polymérisation par métathèse de Grignard. La saponification des copolymères esters a conduit aux polyacides correspondants. Les propriétés photovoltaïques de ces copolymères ont été étudiées dans des dispositifs à hétérojonctions en volume avec PC61BM comme accepteur. Parmi tous les copolymères amphiphiles, le P3HT-b-P3AcidHT a montré les meilleurs résultats avec un rendement de conversion de 4,2%, une tension de circuit ouvert (Voc) de 0,60 V, une densité de courant de court-circuit (Jsc) de 13,0 mAcm-2, et un facteur de forme (FF) de 0,60. Toutes les molécules conjuguées Donneur-Accepteur et les polymères ont été caractérisés par des méthodes chimiques et leurs propriétés optiques, électrochimiques, ainsi que les propriétés morphologiques et photovoltaïque ont été étudiés.

Recently, as the fossil fuels strongly decreased, several studies have been conducted in order to exploit solar power as an alternative source of energy. To make this possible with sustainable costs, the attention has been focused on the development of organic photovoltaic solar cells (OPVs) based on polymeric photoactive layer. The aim of this work is to describe the synthesis and characterization of new copolymers, poly[3-(6-fullerenylhexyl)thiophene-co-3-(6-bromohexyl)thiophene], starting from soluble regioregular (PT6BrR) and regiorandom (PT6Br) homopolymeric precursors. These materials are new intrinsically conductive copolymers made of thiophenic units bearing a fullerene and a bromine atom at the end of a hexylic side chain. The obtained homopolymers and copolymers have been widely characterized with different techniques, such as 1H-NMR, FT-IR and UV-Vis spectroscopy, thermal analysis (DSC and TGA) and gel permeation chromatography (GPC). All the synthesized materials were tested as active media in organic solar devices of BHJ type, blended with PC61BM (1:1 w/w) as the acceptor material and as double-cable materials.

L’objectif final de la thèse est l'impression de la couche photo-active ternaire d'une cellule solaire organique en utilisant deux approches: l'une concerne l'apport de nanotubes de carbone (SWCNT) pour améliorer les propriétés de transport, l'autre concerne la préparation de mélanges ternaires de matériaux pour contrôler la couleur des cellules. Les encres pour la couche active incluant des SWCNT fonctionnalisés sont composées d’un donneur d'électron (polymère) (poly(3-hexylthiophène), [P3HT]) et d’un accepteur d'électron ( [6,6]-phényl C61-butyrique ester méthylique d'acide [PCBM]) et ont été développées pour la fabrication de cellules inversées. Ces cellules sont réalisées sur substrats de verre pour l'optimisation de leurs performances, puis sur substrats plastiques pour les applications. Diverses couches d'interfaces ont été testées, qui incluent l'oxyde de zinc (ZnO, couches obtenues par pulvérisation ionique (IBS) ou à partir de solutions de nanoparticules) pour la couche de transport d'électrons et le PEDOT:PSS, le P3MEET, le V2O5 et le MoO3 pour la couche de transport de trous. Des essais ont été effectués avec et sans CNT afin d’étudier leur impact sur les performances. Des résultats similaires sont obtenus dans les deux cas. Il était attendu que les CNT améliorent les performances, ce qui n’a pas été observé pour le moment. Des travaux supplémentaires sont donc nécessaires au niveau de la formulation de la couche active.Avec trois polymères de couleur rouge (P3HT), bleu (B1) et vert (G1), nous avons préparé des mélanges ternaires efficaces permettant l'obtention de couleurs jusque là indisponibles . Nous avons fait une étude sur le piégeage et les mécanismes de diodes parallèles associés aux mélanges. En général, nous avons constaté que les mélanges ternaires de polymères bleu et vert peuvent être décrits par une mécanisme de diodes parallèles, sans entrainer de perte de performances, ce qui n'est pas possible pour les systèmes P3HT:B1 :PCBM et P3HT:G1:PCBM qui se piègent mutuellement. L’objectif final du projet est l'impression de la couche photo-active ternaire d'une cellule solaire organique, composites ternaires (polymère:polymères:acceptor) ou dopés avec les SWCNT. Cette étape nécessite encore des développements futurs
Two approaches were followed to achieve increased control over properties of the photo-active layer (PAL) in solution processed polymer solar cells. This was accomplished by either (1) the addition of functionalized single-walled carbon nanotubes (SWCNTs) to improve the charge transport properties of the device or (2) the realization of dual donor polymer ternary blends to achieve colour-tuned devices.In the first component of the study, P3HT:PC61BM blends were doped with SWCNTs with the ambition to improve the morphology and charge transport within the PAL. The SWCNTs were functionalized with alkyl chains to increase their dispersive properties in solution, increase their interaction with the P3HT polymer matrix, and to disrupt the metallic characteristic of the tubes, which ensures that the incorporated SWCNTs are primarily semi-conducting. P3HT:PCBM:CNT composite films were characterized and prepared for use as the photoactive layer within the inverted solar cell. The CNT doping acts to increase order within the active layer and improve the active layer’s charge transport properties (conductivity) as well as showed some promise to increase the stability of the device. The goal is that improved charge transport will allow high level PSC performance as the active layer thickness and area is increased, which is an important consideration for large-area inkjet printing. The use of ternary blends (two donor polymers with a fullerene acceptor) in bulk-heterojunction (BHJ) photovoltaic devices was investigated as a future means to colour-tune ink-jet printed PSCs. The study involved the blending of two of the three chosen donor polymers [red (P3HT), blue (B1), and green (G1)] with PC61BM. Through EQE measurements, it was shown that even devices with blends exhibiting poor efficiencies, caused by traps, both polymers contributed to the PV effect. However, traps were avoided to create a parallel-like BHJ when two polymers were chosen with suitable physical compatibility (harmonious solid state mixing), and appropriate HOMO-HOMO energy band alignment. The parallel diode model was used to describe the PV circuit of devices with the B1:G1:PC61BM ternary blend

L’interesse della ricerca scientifica sta crescendo sempre più tra i materiali a base tiofenica, spinta dalle loro sorprendenti proprietà funzionali e semiconduttive. Gli oligotiofeni trovano infatti applicazione in molti campi interdisciplinari, in particolare nei dispositivi fotovoltaici organici. In questo studio è stato sintetizzato un nuovo eptamero T7-Bz-TSO2 con sequenza D-A1-D-A-D-A1-D grazie alla reazione di cross-coupling Suzuki-Miyaura catalizzata da un complesso di palladio e assistita da microonde. Questo lavoro si è incentrato sull’introduzione di una nuova unità tiofenica S,S-diossidata lungo la catena oligomerica principale e sullo studio delle diverse proprietà ottiche ed elettrochimiche del nuovo materiale, utilizzato come strato fotattivo in una cella solare organica di tipo bulk heterojunction (BHJ). Lo studio dei parametri di cella ha rivelato una promettente natura ambipolare del T7-Bz-TSO2, non comune in questa classe di composti e di grande interesse per lo sviluppo di dispositivi fotovoltaici organici.

Negli ultimi anni sono stati sintetizzati numerosi oligomeri e polimeri del tiofene che, grazie alle loro proprietà di semiconduttori, hanno trovano largo impiego in molti campi di interesse tecnologico come, ad esempio, transistor ad effetto di campo, diodi elettroluminescenti, dispositivi ottici non lineari e celle fotovoltaiche. Più recentemente, oligomeri tiofenici ossidati allo zolfo hanno trovato applicazione sia in campo elettronico, come materiali accettori in blenda con il poli(3-esiltiofene) (P3HT) usato come materiale donatore, in celle solari di tipo Bulk Hetero Junction (BHJ), ma anche in campo biologico come marcatori fluorescenti di proteine e oligonucleotidi. Tuttavia la sintesi di queste specie richiede condizioni di reazione spinte e al contempo rischiose dovute all’utilizzo in largo eccesso di agenti ossidanti molto forti. Uno degli obiettivi di questa tesi è stato lo sviluppo di metodi più versatili per la mono e di-ossidazione selettiva allo zolfo del tiofene di building-blocks dibromurati di diversa natura. Successivamente i building-blocks S-monossido e S,S-diossido derivati sono stati impiegati per la sintesi di oligomeri e polimeri tramite reazioni di cross-coupling Palladio catalizzate. I composti finali sono stati caratterizzati sia dal punto di vista spettroscopico UV-Vis che elettrochimico, mettendo in evidenza le relazioni che esistono fra gli andamenti dei dati sperimentali ottenuti con il diverso stato di ossidazione dei composti tiofenici diversamente sostituiti. Infine i composti finali sono stati testati sia in campo fotovoltaico che biologico.

In questo progetto di tesi viene presentata la sintesi di due polimeri tiofenici solubili in acqua con caratteristiche interessanti per la costruzione di celle solari “green”: il poli[3-(6-dietilamminoesil)tiofene] (PT6NEt) e il poli[3-(6-pirrolidinilesil)tiofene] (PT6Pir). Il PT6NEt è stato ottenuto per sostituzione nucleofila del precursore PT6Br utilizzando dietilammina in THF come nucleofilo; il successivo trattamento con bromoetano ha permesso di ottenere il sale d’ammonio quaternario. Il PT6Pir è stato ottenuto in maniera analoga, mediante sostituzione nucleofila del Br con pirrolidina ottenendo direttamente un polimero solubile in acqua. Le strutture dei prodotti sono state caratterizzate mediante analisi FT-IR, NMR e UV-Vis. I polimeri hanno mostrato un notevole effetto batocromico in presenza di un non-solvente. E’ stato inoltre possibile determinare i valori di energy gap per i due polimeri che risultano simili a quelli del P3HT (poli(3-esiltiofene), utilizzato come riferimento). This thesis proposes the synthesis of two water soluble thiophene polymers with interesting characteristics for the construction of "green" solar cells: poly[3-(6-diethylaminohexyl)thiophene] (PT6NEt) and poly[3-(6-pyrrolidinylhexyl)thiophene] (PT6Pir). PT6NEt was obtained by nucleophilic substitution on PT6Br using diethylamine in THF as a nucleophile; the following treatment with bromoethane led to the quaternary ammonium salt. PT6Pir was obtained by nucleophilic substitution of Br with pyrrolidine directly obtaining a water soluble polymer. The obtained products were characterized by FT-IR, NMR and UV-Vis analysis. They showed a remarkable bathochromic effect in presence of a non-solvent. The energy gap values for the two polymers were similar to that of the reference polymer poly(3-hexylthiophene) (P3HT).

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 book reviews recent research and new trends in the area of solar cell materials. Topics include fabrication methods, solar cell design, energy efficiency and commercialization of next-generation materials. Special focus is placed on graphene and carbon nanomaterials, graphene in dye-sensitized solar cells, perovskite solar cells and organic photovoltaic cells, as well as on transparent conducting electrode (TCE) materials, hollow nanostructured photoelectrodes, monocrystalline silicon solar cells (MSSC) and BHJ organic solar cells. Also discussed is the use of graphene, sulfides, and metal nanoparticle-based absorber materials.