Rozprawy doktorskie na temat „Organic-inorganic lead halide perovskite solar cells”

Abstract Methylammonium lead (II) iodide has recently attracted considerable interest which may lead to substantial developments of efficient and inexpensive industrial photovoltaics. The application of this material as a light-absorbing layer in solid-state solar cells leads to impressive efficiency of over 22% in laboratory devices. However, for industrial applications, fundamental issues regarding their thermal and moisture stability need to be addressed. MAPbI3 belongs to the perovskite family of materials with the general formula ABX3 ,where is the organic cation (methylammonium) which is reported to be a major source of instability. In this work, a variety of alkyammonium lead (II) iodide materials have been synthesized by changing the organic cation, to study the relationship between the structural and physical properties of these materials. [(A)PbI3] and (A)PbI4 series were studied. Three dimensional (3D) networks (MAPbI3,MAPbBr3), two dimensional (2D) layered systems (BdAPbI4, HdAPbI4, OdAPbI4), and one dimensional (1D) columns (EAPbI3, PAPbI3, EAPb2I6) were found for the materials. [PbI6] octahedral structural units were repeated through the material network depending on the dimensionality and connectivity of the materials. Where a bulkier cation was introduced, the crystallographic unit cell increased in size which resulted in lower symmetry crystals. The connectivity of the unit cells along the material networks was found to be based on corner-sharing and face-sharing. Lower dimensionality resulted in larger bandgaps and lower photoconductivity, and hence a lower light conversion efficiency for the related solar cells. The thermal and moisture stability was greater in the 1D and 2D materials with bulkier organic cations than with methylammonium. In total, an overview is provided of the relationship between the chemical dimensionality and physical properties of the organic-inorganic lead halide materials with focus on the solar cell application.
Svenska sammandrag: Metylammoniumbly(II)jodid har under de senaste åren genererat ett stort intresse som ett möjligt material for utveckling av effektiva och på industriell skala billiga solceller. Detta material har använts som ljusabsorberande skikt i fasta solceller med imponerande omvandlingseffektiviteter på över 22% för solceller i laboratorieskala. För att denna nya typ av solceller ska bli intressanta för produktion på industriell skala, så behöver grundläggande frågeställningar kring materialens stabilitet avseende högre temperaturer och fukt klargöras. MAPbI3 har formellt perovskitstruktur med den allmänna formel ABX3, där A utgörs av den organiska katjonen (metyammoniumjonen) och som kan kopplas till materialets instabilitet. I denna avhandling har olika alkylammoniumbly(II)jodidmaterial syntetiserats där den organiska katjonen modifierats med syftet att studera växelverkan mellan struktur och fysikaliska egenskaper hos de resulterande materialen. Material av olika dimensionalitet erhölls; tredimensionella (3D) nätverk (MAPbI3, MAPbBr3), tvådimensionella (2D) skiktade strukturer (BdAPbI4, HdAPbI4, OdAPbI4), och endimensionella (1D) kedjestrukturer (EAPbI3, PAPbI3, EAPb2I6). Flera nya lågdimensionella material (2D och 1D) tillverkats och karaktäriserats för första gången. Enkristalldiffraktometri har använts för att erhålla materialens atomära struktur. Strukturen hos material tillverkade i större mängder konfirmerades genom jämförelse mellan resultat från pulverdiffraktion och enkristalldiffraktion. Den oktaedriska strukturenheten [PbI6] utgör ett återkommande tema i materialen sammankopplade till olika dimensioner. Då större organiska katjoner används karaktäriseras i regel strukturerna av större enhetsceller och lägre symmetri. De lågdimensionella materialen ger typiskt störe elektroniskt bandgap, lägre fotoinducerad ledningsförmåga och därför sämre omvandlingseffektiviteter då de används i solceller. De lågdimensionella materialen (1D och 2D) som baseras på de större organiska katjonerna uppvisar bättre stabilitet med avseende på högre tempereratur och fukt. De tvådimensionella materialens elektroniska struktur har karaktäriserats med hjälp av röntegenfotoelektronspektroskopi, liksom röntgenabsorptions- och emissionsspektroskopi. Resultat från teoretiska beräkningar stämmer väl överens med de experimentella resultaten, och de visar att materialens valensband huvudsakligen består av bidrag från atomorbitaler hos jod, medan atomorbitaler från bly främst bidrar till edningsbandet. Sammantaget erbjuder avhandlingen en översikt av sambandet mellan kemisk dimensionalitet och fysikaliska egenskaper hos ett antal organiska/oorganiska blyhalogenidmaterial med fokus på tillämpning i solceller.

QC 20170123

Ces onze dernières années ont vu apparaitre les pérovskites organiques inorganiques hybrides (HOIPs) comme un passionnant domaine de recherche pour leur application potentielle dans les technologies du photovoltaïque (PV) en raison de leurs exceptionnelles propriétés optoélectroniques et de leur facilité de mise en oeuvre. Cependant, les matériaux HOIPs ont plusieurs inconvénients dont leur manque de stabilité en conditions opérationnelles. Améliorer celle-ci est l'un des plus grands défis à relever avant commercialisation. La formule générale est (A1,A2,A3,A4)Pb(X1,X2)3, où les sites A occupés par une distribution de 1 à 4 cations métalliques/organiques et les sites X par celle d’anions halogénures. Les défauts lacunaires natifs sont considérés comme une cause possible de dégradation des cellules solaires HOIPs. L'objectif de ce travail est de comprendre le rôle des défauts dans la stabilité à long terme des matériaux PV HOIPs. A cette fin, des défauts primaires ont été introduits de manière contrôlée par irradiation avec des électrons de haute énergie (1MeV) dans des lots de couches et cellules solaires (SCs) à base de divers composés HOIPs. Il s'agit notamment du prototype PV HOIPs, MAPbI3 (A1PbX13), et de nouveaux composés mixtes d’halogénures à triple ou quadruple cations, (CsMAFA)Pb(I1-xBrx)3 (A3PbX23) ou (GACsMAFA)Pb(I1-yBry)3 (A4PbX23). Les couches sont fabriquées selon la même procédure que les couches actives SCs et, ensuite, traitées dans des conditions similaires. Pour A1PbX13/A3PbX23, la structure SC est de type p-i-n avec des couches organiques pour le transport des trous et des électrons (HTL/ETL). Les couches sont déposées sur le substrat verre/ITO/HTL (PEDOT:PSS) sans ou avec couche supérieure ETL (PCBM). Pour A4PbX23, la structure SC est de type n-i-p avec des couches ETL inorganiques (TiO2) et HTL organiques (Spiro-OMeTAD). Les couches sont directement déposées sur du verre.La spectroscopie d'annihilation de positons donne une évidence directe de l'existence de défauts lacunaires natifs et induits par irradiation dans chaque composé. Les spectres d’absorbance en fonction de l’énergie montrent que le vieillissement naturel et après irradiation génère différentes populations de défauts dans chaque composé. De plus, celles-ci pour A1PbX13 et A3PbX23 diffèrent selon l'absence ou la présence de la couche supérieure ETL. Les populations de défauts évoluent pendant au moins 3 mois. Le vieillissement modifie (i) la bande interdite, (ii) les queues de bande de conduction/valence et (iii) l'absorption optique via des niveaux électroniques profonds. Les effets d’illumination sous laser varient aussi en fonction du vieillissement. L’asymétrie des pics de photoluminescence (PL) dans chaque composé sous illumination laser continue reflète une superposition de raies d’émission gaussiennes à énergie, FWHM et hauteur évoluant avec le temps d'illumination. Les transitions d'émission impliquent des niveaux électroniques localisés peu profonds dans A3PbX23/A4PbX23 et résonnants dans A1PbX13. De tels effets durent au moins 3 mois dans A4PbX23. Ces niveaux électroniques sont attribués à des populations de défauts spécifiquement induits par illumination. Le vieillissement naturel et après irradiation donne des spectres PL à décroissance temporelle résolue en une ou deux exponentielles. Le nombre et la durée de vie sont fortement influencés par l’irradiation initiale et la composition. Une amélioration frappante du fonctionnement PV pour le type SC p-i-n est induite par le vieillissement dû à l'irradiation. Le rendement quantique externe et les performances PVs ont des valeurs plus élevées pour l’état irradié que de référence durant 6 à 12 mois de vieillissement. Cela prouve que l'ingénierie des défauts par irradiation d'électrons à haute énergie a le potentiel de fournir des voies de traitement innovantes pour améliorer la stabilité à long terme des performances photovoltaïques HOIPs
During the last eleven years, Hybrid Organic Inorganic Perovskites (HOIPs) materials have emerged as an exciting topic of research for potential application in solar cell technologies due to their outstanding optoelectronic properties and processing advantages. However, HOIPs materials suffer from several drawbacks with, in peculiar, their lack of stability under operational conditions (light, bias, environment…). To improve this stability is one of the biggest challenges to be addressed before commercialization. The general formula for HOIPs is (A1,A2,A3,A4)Pb(X1,X2)3, where the A sites can be occupied by a distribution of 1 to 4 metallic/organic cations and X sites with halide anions. The role of native vacancy defects has been questioned as a possible cause for HOIPs solar cells degradation. The aim of this work is to understand the defect role in long term stability of HOIPs materials for photovoltaics. For this reason, primary defects were introduced in a controlled way via high energy electron irradiation (1MeV) in sets of layers and solar cells (SCs) fabricated using various HOIPs compounds. Those include the photovoltaic HOIPs prototype, MAPbI3 (A1PbX13), and emergent triple or quadruple cation mixed halide HOIPs, (CsMAFA)Pb(I1-xBrx)3 (A3PbX23) or (GACsMAFA)Pb(I1-yBry)3 (A4PbX23). The HOIPs layers are fabricated according to the same procedure as the HOIPs active SC layers and, subsequently, treated in similar conditions. For A1PbX13 and A3PbX23, the solar cells are of the p-i-n structure with organic hole and electron transport layer (HTL/ETL). The HOIPs layers are deposited on the glass/ITO/HTL (PEDOT:PSS) substrate without or with the top ETL layer (PCBM). For A4PbX23, the solar cells are of the n-i-p type with inorganic ETL (TiO2) and organic HTL (Spiro-OMeTAD) layers. The layers are directly deposited on glass without the ETL layer.Positron Annihilation Spectroscopy (PAS) gives direct evidence for native vacancy-type defects and irradiation induced ones in layers of each HOIP compound. The energy dependence of absorbance shows that natural and after irradiation ageing generates different defect populations in each HOIP compound. These populations strikingly also differ depending on the absence or presence of the top ETL layer for the A1PbX13 and A3PbX23 compounds. The defect populations evolve over ageing duration as long as 3 months. The prominent effects of ageing include (i) band gap modification, (ii) tailing of conduction/valence band extrema and (iii) optical absorption via deep subgap electronic levels. Illumination effects under laser also vary with ageing for each HOIP compound. Asymmetric photoluminescence (PL) peaks in each compound under continuous laser illumination reflect that radiative emission involves Gaussian emission rays with energy, FWHM and height evolving with illumination time. The emission transitions involve shallow localized electronic levels in A3PbX23 and A4PbX23 and resonant ones in A1PbX13. These electronic levels are attributed to specifically illumination-induced defect populations. Natural and after irradiation ageing result in PL decay lifetime spectra resolved into one or two exponential decay components. The decay components number and lifetime are strongly affected by the initial production of irradiation defects and HOIPs composition. Such effects last over 3 months at least in A4PbX23. The p-i-n solar cells exhibit most striking irradiation ageing induced photovoltaics performance. The External Quantum Efficiency (EQE versus photon energy) and the photovoltaic performance (I-V under illumination) of the irradiated solar cells have higher values than those in the reference SCs after 6 to 12 months of ageing. This gives evidence that defect engineering via high energy electron irradiation has a potential for providing innovative processing pathways to enhance the long-term stability of HOIPs photovoltaic performance

In the last 10 years, the research interest has been drawn towards the hybrid organic-inorganic halide perovskites, an innovative material characterized by remarkable optoelectronic properties and by its simplicity of fabrication; hybrid halide perovskites are currently being employed as active material in solar cells, X-ray photodetectors and light emitting devices. The following thesis presents the characterization of two perovskite-based materials. The first is a methylammonium lead iodide (MAPbI3) thin film solar cell, which has been fabricated and characterized at the University of Konstanz (Germany), with the aim to optimize the deposition procedure. The second material is a methylammonium lead bromide (MAPbBr3) single crystal that have been characterized at the University of Bologna with surface photovoltage and photocurrent spectroscopies, as a function of the deposited dose of X-rays in order to monitor the induced effects of radiation. After the exposure to X-rays, the exciton binding energy, calculated from the surface photovoltage spectra, has been found to increase by 20 meV with respect to the not irradiated sample. A similar result has been found with the photocurrent spectroscopy. The reasons for the increase in binding energy is discussed and attributed to a change in polarizability of the single crystal. The recovery of the crystals has been registered as well and has shown that the material is able to return to the initial condition after just few hours from the last X-ray's deposition.

The endeavor to have more efficient solar cells and as environmentally beneficial as possible are the driving forces for this work. The way to reach this is by research to better the understanding of the mechanisms and parameters that govern the performance of solar cells. New materials are essential to develop because the current ones lack stability and are water, temperature and UV-radiation sensitive. In this work the lead (Pb2+), which is poisonous and hazardous is intended to be replaced in the organic metal halide (OMH) perovskite structure. This is tested with gold or silver combined with bismuth and silver by itself. Also trimethylsulfonium gold or silver iodides are investigated. The methylammonium cation is also substituted to cesium. The perovskite material both absorbs light and transports charges in the solar cells. Materials based on AuI/AgI, BiI3 and CH3NH3I and AuI/AgI and [Me3S]I and AgI, BiI3 and CsI were synthesized and analyzed by XRD on thin film and mesoporous substrate and Raman spectroscopy to determine material structure and bonding. J-V measurements were performed to see the function in solar cells. After this conductivity and absorption parameters were determined by an electrical conductivity test and UV-vis absorption spectroscopy. XRD measurements indicate that the perovskite structure could have been obtained because the materials match with the XRD spectra of [20] foremost T3, T5 and T6, Cs1 and Cs2. In T7 some new structure is formed. The bismuth could be partially substituted by silver as the metal cation. The samples are quite amorphous, but still containing crystalline peaks, the product material could be a mixture of a crystalline and an amorphous phase. The crystalline phase could have the desired perovskite structure. To have mesoporous TiO2 as substrate seem to enhance a more crystalline structured material. All the materials seem to have formed some new structures because the pure reactants does not seem to be present, exceptions could be P1 and T1 that contained AuI. The change of cation from methylamine to cesium though results in a shift of the peak positions because of the change of cation size as in [20], but the structure is most likely the same. Raman spectroscopy indicate that there is a change in structure, some new bond being present, when increasing the methylamine ratio for the presumed methylammonium silver bismuth iodide perovskites. This concerns materials T5, T6, T7 with increasing ratio of methylamine. This new bond is most pronounced in T7 where the methylamine content is the highest. Both Silver and bismuth iodide bonds seem to be present and cannot be coupled to be the pure reactants recrystallizing and some new bonds of these are present in all materials to some extent. The organic bond vibration has low intensity and might indicate that there is not so much organic cation present in the product and thus the probability of having the desired product anion decreases. The solar cells made with Spiro-OMeTAD were 700-4000 times more efficient than those made with Sulphur polymer HTM. Solar cells made with Spiro-OMeTAD as HTM gives slightly higher efficiency when increasing the methylammonium cation ratio. For cesium as cation the combined metal cation constellation with bismuth and silver gives a little higher efficiency than bismuth alone. Methylammonium as cation gives a higher efficiency than cesium. Solar cells made with Sulphur polymer HTM show approximately 3-30 times higher efficiency with methylammonium as cation compared to cesium as cation. HTM material seem to affect the perovskite material making some of the cells completely transparent and some of them paler, water in the solvent chlorobenzene can be a possible explanation. The transparency can be the reason for the low efficiency obtained for the solar cells. Also the measurement methodology of these solar cells can also have been false, measuring the contacts, and the etching procedure could be another source of this. The solar cells had quite low efficiencies compared to [20], although same presumed material and procedure has been used and thus there might be something wrong in the accuracy of the manufacturing. The cells should probably been made several times and possible sources of error should be analyzed and corrected for. The materials were all relatively conductive. P1 gave the highest conductivity, almost three times higher than for methylammonium lead iodide that has a conductivity of 1,1x10-4 s/cm [3]. Increasing the methylammonium ratio gave an increase of the conductivity both with bismuth and silver as metal cations and silver alone. The increase of the methylammonium ratio might result in a new structure formed which has lattice planes that are more conductive. A change of gold to silver for the trimethylsulfonium iodide materials gave a large decrease in conductivity. The materials have different absorption curves meaning that they have different bandgaps and this indicates differences in structure. The bandgaps of all materials are indirect contrary to what is proven to be the case for perovskites that are believed to have direct bandgaps in general. To have indirect bandgaps requires a shift in momentum in the electronic transitions and is not as beneficial as having direct bandgaps. Compared to methylammonium lead iodide that has a direct bandgap of 1,6 eV, the bandgaps are at least 0,5 eV higher and range between 2,2-2,36 eV. P1 had a low bandgap of 1,6 eV meaning it absorbs a wide range of wavelengths. The conductivity does not seem to be the obstacle and the cells that are not transparent absorb light. It is highly possible that the low solar cell performance, at least to a certain extent, has to do with the production process. The low scan rate could also affect the low efficiencies and HTM Spiro-OMeTAD should be used. Currently the efficiency of the perovskite materials with silver/bismuth, gold/bismuth and silver are too low, and not able to substitute lead in the perovskite structure solar cells. Neither trimethylsulfonium gold or silver iodide cells nor cesium perovskites have enough efficiency at present. The conductivities for the materials are promising and the materials that are not completely transparent absorb light.
Strävan att utveckla effektivare solceller och så miljövänliga som möjligt är drivkrafterna för det här arbetet. För att uppnå detta krävs forskning för att förbättra förståelsen för vilka mekanismer och parametrar som styr hur väl solcellerna fungerar. Det är nödvändigt att ta fram nya material, då de nuvarande brister i stabilitet, de är framförallt känsliga för vatten, temperatur och UV-strålning. I det här arbetet är syftet att byta ut bly (Pb2+), som är giftig och kopplad till hälsorisker, i den organiska metall halid (OMH) perovskit strukturen. Detta görs med guld eller silver i kombination med vismut och silver självt. Även trimetylsulfonium- guld eller silver undersöks. Metylammonium katjonen substitueras också mot cesium. Perovskit material absorberar både ljus och transporterar laddningar i solceller. Material baserade på AuI/AgI, BiI3 och CH3NH3I and AuI/AgI och [Me3S]I and AgI, BiI3 and CsI syntetiserades. Dessa analyserades, med XRD på dels ett substrat av tunn film och dels ett mesoporöst och Raman spektroskopi, för att bestämma strukturen på materialet och bindningar. J-V mätningar utfördes för att se hur materialen fungerade som solceller. Efter detta utfördes mätningar av konduktiviteten och absorptions parametrar bestämdes genom ett elektriskt konduktivitetstest respektive UV-vis absorptions spektroskopi. XRD mätningarna indikerar att perovskit strukturen kan ha erhållits eftersom spektrumen överensstämmer med de i [20], framförallt för T3, T5 och T6, Cs1 och Cs2. I T7 bildas någon ny struktur. Vismut skulle kunna vara delvis utbytt mot silver som metalkatjon. Proven är relativt amorfa, men uppvisar kristallina toppar och produkten skulle kunna vara en blandning av en kristallin och amorf fas, där den kristallina fasen skulle kunna ha den eftersträvade perovskit strukturen. Mesoprös TiO2 som substrat verkar öka graden av kristallinitet hos materialen. Samtliga material verkar ha bildat någon ny struktur eftersom reaktanterna i sin rena form inte verkar finnas. Undantag skulle kunna vara P1 och T1, vilka innehåller AuI. Bytet av katjon från metylammonium mot cesium resulterar i ett skifte av topparna troligen beroende av skillnaden i storlek mellan katjonerna, liksom påvisas i [20], men strukturen är förmodligen densamma. Raman spektroskopin indikerar en förändring i strukturen, någon ny bindning finns, hos materialen när metylammonium andelen ökas för de förmodade metylammonium silver vismut jodid perovskiterna. Detta gäller materialen T5, T6, T7, där andelen metylammonium ökar. Den nya bindningen är mest uttalade i T7, där metylammonium andelen är den högsta. Både silver och vismut jodid bindningar verkar finnas och kan inte kopplas till att de rena reaktanterna har rekristalliserats och nya bindningar av dessa finns i alla material till en viss grad. Den organiska bindningens vibration har låg intensitet och kan tyda på att det inte finns så mycket organisk katjon i produkten och således minskar sannolikheten att ha den eftersträvade anjon produkten. Solcellerna gjorda med Spiro-OMeTAD var 700-4000 gånger mer effektiva än dom gjorda med Svavel polymer HTM. För solcellerna gjorda med Spiro-OMeTAD som HTM ger en ökning av metylammonium katjon andelen en ökad effektivitet. För cesium som katjon med den kombinerade metalkatjon konstellationen med vismut och silver, blir effektiviteten högre än om vismut är metalkatjon självt. Metylammonium som katjon ger en högre effektivitet än cesium. Solceller gjorda med Svavel polymer HTM visar ungefär 3-30 gånger högre effektivitet med metylammonium som katjon jämfört med cesium som katjon. HTM materialet verkar påverka perovskit materialet och göra några av cellerna helt transparenta och de andra blekare. Klor benzen användes som lösningsmedel och denna kan ha innehållit vatten och kan vara orsaken till färgskiftningen. Detta kan vara orsaken till den låga verkningsgraden som erhölls för solcellerna. En annan möjlig förklaring skulle kunna vara metoden för mätningarna. Denna kan ha varit felaktig, då kontakten troligen har varit det som har mätts och etsningsprocessen skulle kunna vara en orsak till detta. Solcellerna uppvisar ganska låg effektivitet i jämförelse med [20], trots att samma material och procedur har använts och således kan det vara något fel i precisionen av framställningen. Cellerna skulle förmodligen gjorts om ett antal gånger och möjliga felkällor borde utretts och åtgärdats. Materialen var överlag relativt konduktiva. P1 gav den högsta konduktiviteten, nära tre gånger högre än metylammonium bly jodid, som har en konduktivitet på 1,1x10-4 s/cm [3]. En ökning av andelen metylammonium gav en ökning av konduktiviteten både med vismut och silver som metalkatjon och silver självt. Ökningen av andelen metylammonium skulle kunna resultera i ett en ny struktur uppkommer som har plan som är mer konduktiva. Utbytet av guld mot silver för trimetylsulfonium jodid materialen gav en markant sänkning av konduktiviteten. Materialen har olika absorptionskurvor vilket innebär att de har olika bandgap och detta indikerar olikheter i strukturen. Bandgapen för alla material är indirekta, trots att bandgapen för perovskiter i regel är direkta. Att ha indirekta bandgap kräver ett skifte i momentum i de elektroniska energiöverföringarna och är inte så fördelaktigt som att ha direkta bandgap. I jämförelse med metylammonium bly jodid, som har ett direkt bandgap på 1,6eV, är bandgapen minst 0,5 eV högre och varierar mellan 2,2-2,36 eV. P1 hade ett lågt värde på bandgapet, 1,6 eV, vilket innebär absorption av ett brett spektrum av våglängder. Konduktiviteten verkar inte vara den faktor som är orsaken till den låga effektiviteten hos solcellerna och de celler som inte är transparenta absorberar ljus. Det är högst troligt att den låga effektiviteten har sin förklaring, åtminstone delvis, i produktionsprocessen för solcellerna. Den relativt låga skanningshastigheten kan också vara en orsak för den låga effektiviteten och HTM Spiro-OMeTAD bör användas. I dagsläget är effektiviteten för perovskitmaterialen med silver/vismut, guld/vismut och silver för låg och har inte möjlighet substituera bly i perovskit solceller. Inte heller trimetylsulfonium guld eller silver jodid cellerna och inte heller cesium perovskiternas effektivitet räcker till i dagsläget. Konduktiviteten för materialen är lovande och materialen som inte är transparenta absorberar ljus.

Der Schwerpunkt der vorliegenden Arbeit liegt in der Charakterisierung der elektronischen Eigenschaften von hybriden organisch-anorganischen Perowskit (HOIP)-Schichten während der Schichtbildung und in verschiedenen Umgebungen mittels Photoelektronenspektroskopie (PES). Insbesondere wird der Methylammonium-Blei-Iodid-Chlorid-Perowskit (MAPbI3-xClx) untersucht. Als erstes werden Änderungen in den elektronischen Eigenschaften, der Zusammensetzung, sowie der Kristallstruktur mittels PES, Flugzeit-Sekundärionenmassenspektrometrie, sowie Röntgendiffraktometrie mit streifendem Einfall analysiert. Die Resultate weisen auf die entscheidende Rolle von Chlor im texturierten Wachstum der Perowskitschicht hin. Die auskristallisierte Perowskitschicht weist eine stärkere n-Typ Eigenschaft auf, welche auf die Änderung der Zusammensetzung während der Schichtbildung zurückgeführt werden kann. Außerdem beweisen die Ergebnisse eindeutig die Ablagerung von Chlor an der Grenzfläche zwischen der Perowskitschicht und dem Substrat. Zweitens werden die separaten Einflüsse von Wasser, Sauerstoff, und Umgebungsluft auf die elektronischen Eigenschaften von MAPbI3-xClx-Schichtoberflächen untersucht. Bereits geringste Wassermengen ähnlich wie im Hochvakuum oder in inerter Umgebung können eine reversible Reduzierung der Austrittsarbeit hervorrufen. Höherer Wasserdampf-Partialdruck führt zu einer Verschiebung des Valenzbandmaximums (VBM) weit vom Fermi-Niveau, sowie zu einer Reduzierung der Austrittsarbeit. Im Gegensatz dazu führt eine Sauerstoffexposition zu einer Verschiebung des VBM in Richtung des Fermi-Niveaus und zu einer Steigerung der Austrittsarbeit. Analog kommt es zu einer Verschiebung von bis zu 0.6 eV bei einer Exposition gegenüber Umgebungsluft, was den vorwiegenden Einfluss von Sauerstoff demonstriert. Die vorliegenden Untersuchungen betonen den kritischen Einfluss der Schichtbildung, der Zusammensetzung, sowie der Umgebungsbedingungen auf die elektronischen Eigenschaften von HOIP.
The present thesis aims at characterizing the electronic properties of solution-processed hybrid organic-inorganic perovskites (HOIPs) in general, and the HOIP methyl ammonium (MA) lead iodide-chloride (MAPbI3-xClx) films, in particular, at different stages, namely from its formation to its degradation, by means of photoelectron spectroscopy (PES). Firstly, the formation of MAPbI3-xClx films upon thermal annealing is monitored by a combination of PES, time-of-flight secondary ion mass spectrometry, and grazing incidence X-ray diffraction for disclosing changes in electronic properties, film composition, and crystal structure, respectively. Overall, the results point to the essential mediating role of chlorine in the formation of a highly textured perovskite film. The film formation is accompanied by a change of composition which leads to the film becoming more n-type. The accumulation of chlorine at the interface between perovskite and the underlying substrate is also unambiguously revealed. Secondly, the separate effects of water and oxygen on the electronic properties of MAPbI3-xClx film surfaces are investigated by PES. Already low water exposure – as encountered in high vacuum or inert conditions – appears to reversibly impact the work function of the film surfaces. Water vapor in the mbar range induces a shift of the valence band maximum (VBM) away from the Fermi level accompanied by a decrease of the work function. In contrast, oxygen leads to a VBM shift towards the Fermi level and a concomitant increase of the work function. The effect of oxygen is found to predominate in ambient air with an associated shift of the energy levels by up to 0.6 eV. Overall, the findings contribute to an improved understanding of the structure-property relationships of HOIPs and emphasize the impact of least variation in the environmental conditions on the reproducibility of the electronic properties of perovskite materials.

碩士
國立清華大學
光電工程研究所
102
This paper proposed a low temperature, solution process, simple process, a large area of the lead halide perovskite organic/inorganic hybrid solar cell. In this paper, in which the use of lead halide perovskite as the photoactive layer. With the high solubility PbCl2 in DMSO to increase the concentration of the precursor solution, and construct organic / inorganic hybrid solar cell. Our device configuration:Glass/ITO/PEDOT:PSS/Perovskite/PCBM/Al belong to normal structure. Suitably selected the hole and the electron transport layer by spin coating and dried to optimize conditions for the performance of the solar cell of the present paper is better. In this paper, Construction of the solar cell efficiency of up to 7.0 %, short-circuit current of 18.1 mA/cm2 has excellent performance. Lead halide perovskite organic / inorganic hybrid solar cell laden with good efficiency and performance advantages of a large area can be to facilitate the production of large-area components toward future development.

碩士
國立臺灣大學
材料科學與工程學研究所
106
Organic-inorganic hybrid lead halide perovskite solar cells have been developed rapidly because its excellent performance. However, the active material is unstable in ambient air, which limits its practical application. Thermal instability of devices states a more fundamental problem. In this thesis, atomic layer deposited inorganic metal oxides was applied to perovskite solar cells devices in order to solve the problem. We first investigated compatibility of perovskite with a variety of metallic precursors and with oxidants, respectively. We concluded criteria of selecting condition of ALD process and choice of precursors that would not damage perovskite. With optimal parameters, devices with ultra-thin atomic layer deposited Al2O3 or TiO2 direct on top of perovskite showed good performance. However, thermal instability of devices still did not improve due to imperfect coverage of oxides layer resulted from lack of nucleation cite on perovskite surface. To solve this problem, we deposited ALD AZO on organic charge transport layer instead. Device of this architecture reached efficiency of 14.6%, and only dropped to 80% of initial value after 1-day storage in glove box at 85℃. The thermal instability was much improved as efficiency of control devices dropped to less than 50% of initial value.

Organic-inorganic lead halide perovskite solar cells (PSC’s) research has seen most notable progress in the field of photovoltaics (PV). The very first PSC was reported in the year 2009 with efficiency of 3.8%, which rapidly increased to the record 25.2% in year 2020. These numbers are quickly approaching the record values achieved for single-crystal silicon based solar cells. Defect tolerant nature of perovskite, high carrier lifetime, ability to tune band-gap and low-cost solution-based processing in addition to many rare properties makes it an ideal candidate for future solar cell technology. These are the properties which also allows this material to find applications beyond PSC’s, like photodetectors, memory, thin-film transistors (TFT’s), etc. However, given the many valuable properties of this class of material, they also come with some dominating properties which hampers commercialization of this PV technology. Problems like, Ion-migration, degradation in ambient condition still have not fully solved and understood. This research field still have many unanswered questions like, finding suitable compositional engineered lattice to make system stable, role of interface on charge transport and device stability. In this work, we have developed a novel process to grow micron size grains of CH3NH3PbI3 (MAPI) using a custom-made glass reactor. Pristine films are spin-coated on substrate in a glove-box and transferred to methyl-amine gas filled reactor followed by annealing of the whole setup in controlled environment. The resulted films are conformal with average grain size of > 1 microns. The resulted films are used to demonstrate the increase in minority carrier lifetime upon annealing in methyl-amine gas environment. Fabricated devices also showed improvement in device performance upon inclusion of large-grained MAPI film as compared to pristine MAPI film. At later stage, optimization of compact layer (c-TiO2) and mesoporous layer (m-TiO2) is performed followed by improved device fabrication methodology. This yield, device efficiency up to 17.5% with high reproducibility. Major contribution in improvement of device efficiency is from fill-factor (FF) of the device. We found that most of the resistive drop is coming from transparent conductive oxide (TCO) and the current path is changed within the TCO to substantially lower the series resistance of the device and improve FF. FF can also be affected by interface defect density and to see the effect of interface defect density on device performance, simulations are performed by taking experimentally found parameters as input to the simulator. High efficiency device fabrication involves deposition of c-TiO2 at 250oC in ALD chamber and thermal annealing of meso-TiO2 at 500oC for 1 hour, increasing the thermal budget of the device. To address this problem, we replace the conventional FTO/TiO2(c)/TiO2(m) stack with Aluminum doped zinc oxide (AZO), considerably simplifying the fabrication process and reducing thermal budget. Photoelectron spectroscopy suggests that AZO is an effective ETL for perovskite (MAPI) thin films, with a large valence band-offset and a small conduction band offset, but with a possible path for carrier recombination at the interface. We show that treating the surface of AZO with ozone gas (AZO:O3) improves the charge carrier extraction at the interface and open-circuit voltage (Voc) and efficiency (η) of 1.03 V and 10.5% respectively are achieved. Given the stability issue of the MAPI, couple of inorganic materials are explored as potential candidate as solar absorber. First material is barium bismuth oxide (BaBiO3, BBO), thin-films of which are deposited by pulsed laser deposition (PLD). Complete electronic band-diagram of BBO is constructed and TiO2 has been used to make single-sided type-2 heterojunction to test BBO’s opto-electronic properties. Second material is cesium titanium bromide (Cs2TiBr6, CTB), thin-films of which are deposited by thermal annealing of cesium bromide (CsBr) thin-films in titanium bromide (TiBr4) vapors in a glove-box. Proof-of-concept CH3NH3PbI3 device with efficiency of 3.2% has been shown on flexible stainless steel (SS). Also, photodetectors have been made based on gold and carbon-based electrode and comparison has been made. This work provides fabrication and characterization of high-efficiency perovskite solar cell and understanding on charge transport across interface in planar device.

碩士
國立臺灣師範大學
化學系
104
Inorganic-organic perovskite solar cells are one of the most significant materials because of its high absorption and power conversion effiency. In this study, the architecture of our planar heterojunction perovskite solar cells is FTO / TiO2 / CH3NH3PbI3-xClx / spiro-OMeTAD / Au. Because this type of solar cell is easily affected by the morphology of perovskite layer, many studies tried to control the morphology of it to improve the effiency. In our work, we synthesized pyrite iron(II) sulfide nanocrystals (FeS2 NCs) with respectively different ligands acting as additive. Each FeS2-ligand with different concentrations is added separately into perovskite precursor solution. Compared with the pristine device, the FeS2-added one shows obviously higher Short circuit current (Jsc) and lower Open circuit voltage (Voc). The as-prepared cells were analyzed in various techniques, including SEM, XRD, Visible Absorption Spectroscopy and EQE, and show significant morphological change in perovskite layer, which dominates the cell’s efficiency.

碩士
國立臺南大學
電機工程學系碩博士班
104
This post thesis research, we will successfully applied the perovskite copper thiocyanate solar cell P-type buffer layer, we will be formulated as a powdercopper thiocyanate solution was spin-coated to be made into film, and from energy level (Conduction band) using copper thiocyanate can be seen also reduce carrier recombination, and therefore can have a higher open-circuit voltage and short circuit current density, conversion efficiency of the element can be improved- We use the PEDOT: PSS element made of the photoelectric conversion efficiency of only 11%, and we can see that the use of copper thiocyanate conversion efficiency can be increased to 15.1%. We then without annealing manner, successfully applied to the flexible substrate copper thiocyanate, efficiency can reach 7%.

Solarzellen aus organisch-anorganischen hybriden Perowskithalbleitern gelten als mögliche Schlüsseltechnologie zur Erzeugung günstiger und umweltfreundlicher elektrischer Energie und somit als Meilenstein für die Energiewende. Um die weltweit stetig wachsende Nachfrage an elektrischer Energie zu decken, bedarf es Solarzellentechnologien, welche gleichzeitig eine hohe Effizienz nahe dem Shockley-Queisser-Limit als auch eine hinreichend gute Stabilität aufweisen. Während die Effizienz von Solarzellen auf Basis von Perowskithalbleitern in dem letzten Jahrzehnt eine bemerkenswerte Entwicklung erfahren hat, lassen sich die wesentlichen physikalischen Mechanismen dieser Technologie noch nicht vollständig erklären. Die elektronisch-ionische Mischleitfähigkeit ist eine dieser Eigenschaften, welche die Effizienz und besonders die Stabilität der Perowskit-Solarzelle beeinflusst. Zentrales Thema dieser Arbeit ist daher die Untersuchung von mobilen ionischen Defekten und deren Einfluss auf Solarzellenparametern. Es wird gezeigt, dass die Migrationsraten ionischer Defekte in Perowskit breiten Verteilungen unterliegen. Durch die Anwendung eines neu entwickelten Regularisationsalgorithmus für inverse Laplace-Transformationen und verschiedener Messmoden für transiente Störstellenspektroskopie kann somit geklärt werden, warum sich berichtete ionische Defektparameter aus der Literatur für gleiche Defekte stark unterscheiden können. Dieses grundlegende Verständnis kann angewendet werden, um den Einfluss von kleinen stöchiometrischen Variationen auf die Defektlandschaft zu untersuchen und das Zusammenspiel zwischen elektronischen und ionischen Eigenschaften besser zu verstehen. Der Einsatz der Meyer-Neldel Regel ermöglicht ferner eine Kategorisierung ionischer Defekte in Perowskithalbleitern. Im letzten Teil dieser Arbeit wird gezeigt, dass elektrische und optische Methoden wie intensitätsmodulierte Spektroskopie geeignet sind, um Informationen über mobile Ionen in hybriden Perowskiten zu erhalten. Zusätzlich wird das elektronische Rekombinationsverhalten näher untersucht.
Solar cells made of organic–inorganic hybrid perovskite semiconductors are considered as a possible key technology for the conversion of cheap and environmentally friendly electrical energy and thus as a milestone for the turnaround in energy policy. In order to meet the steadily growing global demand for electrical energy, solar cell tech- nologies are required that are both highly efficient, i.e. close to the Shockley–Queisser limit, and sufficiently stable. While the efficiency of solar cells based on perovskite semi- conductors has undergone a remarkable development in the last decade, the essential physical mechanisms of this technology cannot yet be fully explained. The electronic- ionic mixed conductivity is one of these properties, which influences the efficiency and especially the stability of the perovskite solar cell. The central topic of this thesis is therefore the investigation of mobile ionic defects and their influence on solar cell parameters. It is shown that the migration rates of ionic defects in perovskites are attributed to wide distributions. By application of a newly developed regularisation algorithm for inverse Laplace transform and different measurement modes for deep-level transient spectroscopy, it can thus be clarified why reported ionic defect parameters from the literature for the same defects can differ significantly. This basic understanding can be used to study the influence of small stoichiometric variations on the defect landscape and to better understand the interaction between electronic and ionic properties. Us- ing the Meyer–Neldel rule also allows the characterisation of ionic defects in perovskite semiconductors. The last part of this thesis shows that electrical and optical methods such as intensity-modulated spectroscopy are suitable for obtaining information about mobile ions in hybrid perovskites. In addition, the electronic recombination behaviour is examined more closely.

碩士
國立臺灣師範大學
化學系
103
Perovskite solar cells have been developed rapidly in recent years. Solution processable planar heterojunction perovskite solar cells are seen as a promising low-cost renewable energy technology. The most common device structure is FTO / TiO2 / CH3NH3PbI3-xClx / spiro-OMeTAD / Au. The main difficulties for this type of solar cells are the controls of coverage and morphology of perovskite CH3NH3PbI3-xClx film. In this study, a solution processable pyrite iron(II) sulfide nanocrystals (FeS2 NCs) act as additives. The FeS2 NCs mixed solution is added 5 vol% into the perovskite precursor solution to improve the film formation, the energy conversion efficiency reach 15.95%. Compared with the pristine CH3NH3PbI3-xClx device it has enhanced about 28%. We studied the new perovskite by various analyses, including XRD, Visible Absorption Spectroscopy, EQE, TRPL and SEM. The results showed that this iron(II) disulfide nanocrystals additive can improve the crystallinity of the perovskite film, making it more connective and directional. Therefore, the increased VOC and FF further enhanced the energy conversion efficiency of perovskite solar cells.