Cadmium telluride (CdTe) is a leading thin film photovoltaic (PV) material due to its near ideal band gap of 1.45 eV, its high optical absorption coefficient and availability of various device fabrication methods. Superstrate CdTe solar cells fabricated on glass have to-date exhibited efficiencies of 16.5%. Work on substrate devices has been limited due to difficulties associated with the formation of an ohmic back contact with CdTe. The most promising approach used to-date is based on the use of an interlayer between the CdTe and a metal electrode, an approach that is believed to yield a pseudo-ohmic contact. This research investigates the use of ZnTe and Sb2Te3 as the interlayer, in the development of efficient back contacts. Excellent adhesion and minimum stress are also required of a CdTe thin film solar cell device on a flexible stainless steel (SS) foil substrate. Foil substrate curvature, flaking, delamination and adhesion as a result of compressive strain due to the coefficient of thermal expansion (CTE) mismatch between the flexible SS foil substrate and the solar cell films have been studied. A potential problem with the use of a SS foil as the substrate is the diffusion of iron (Fe), chromium (Cr) and other elemental impurities into the layers of the solar cell device structure during high temperature processing. A diffusion barrier limiting the out diffusion of these substrate elements is being investigated in this study. Silicon nitride (Si3N4) films deposited on SS foils are being investigated as the barrier layer, to reduce or inhibit the diffusion of substrate impurities into the solar cell. Thin film CdTe solar cells have been fabricated and characterized by AFM, XRD, SEM, ASTM D3359-08 tape test, current-voltage (I-V) and spectral measurements. My individual contributions to this work include the Molybdenum (Mo) development, the adhesion studies, the silicon nitride (Si3N4) barrier studies, and EDS and SEM lines measurements and analysis of substrate out-diffused impurities. The rest of my colleagues focused on the development of CdTe, CdS, ZnTe, the CdCl2 heat treatment, and other back contact interlayer materials.

Les pérovskites hybrides halogénées sont une nouvelle classe de semi-conducteurs polyvalents se proposant d'allier hautes performances, bas coût et processabilité en vue d'applications variées comme le photovoltaïque ou l'émission de lumière. Leur développement à grande échelle se heurte cependant à leur faible stabilité dans les dispositifs. Depuis quelques années, des groupes de chercheurs se sont particulièrement intéressés aux pérovskites hybrides à 2 dimensions (2D). Cette sous-catégorie de pérovskite est bien plus stable et offre une meilleure flexibilité chimique que leurs cousines 3D. Cependant, leurs performances restent limitées par la faible maitrise des méthodes de synthèses. En outre, de nombreux efforts sont encore à faire pour la compréhension de leurs propriétés intrinsèques, notamment via l'étude de monocristaux. Nous avons mis au point une méthode de synthèse par diffusion d’anti-solvant (AVC) permettant de synthétiser des monocristaux de pérovskites 2D telles que (PEA)2PbI4 et (PEA)2(MA)Pb2I7. Cette méthode a été de plus adaptée pour la synthèse de couches minces monocristallines. L’incorporation de ces couches minces dans des dispositifs pourrait permettre en théorie de se rapprocher des performances intrinsèques du matériau. Nous avons de plus synthétisé des nouvelles pérovskites 2D fonctionnalisées par des molécules de luminophore en tant que partie organique. L’étude spectroscopique de ces pérovskites met en évidence des probables transferts de charge entre les deux parties organique et inorganique. Ce type de pérovskite pourrait trouver un intérêt dans le photovoltaïque car il permettrait de séparer l’exciton fortement lié dans les pérovskites 2D. / Hybrid halide perovskites are new class of high-end semiconductors that combine high performances, low cost and low temperature proccessability for different application such as photovoltaics or light-emitting devices. Their large-scale commercialization is however hindered by their poor stability. For a few years, many groups started to grow interest in 2-dimensional (2D) hybrid perovskites. This subclass of perovskite is much more stable than their 3D counterparts, and offers more chemical flexibility. Yet their performances are limited by the bad quality of the spin-coated layers. Moreover an increase in the understanding of their intrinsic properties is necessary. This last point could be solved by the study of single crystals. We developped therefore a new anti-solvant, vapor-assisted crystallization (AVC) method for the growth of (PEA)2PbI4 and (PEA)2(MA)Pb2I7. Furthermore, a capped AVC process (AVCC) was developped for the growth of 2D perovskites single crystalline thin films. These films might help getting closer to the intrinsic limits of the material. We also synthesized new 2D luminophore-functionalized perovskite systems. The spectroscopic studies of this material highlighted a possible charge transfer between the two moities of the perovskite. This kind of perovskite could help improving the photovoltaic performances of 2D perovskite thanks to the splitting of the strongly bounded exciton.

abstract: The primary goal of this thesis is to evaluate the influence of ethyl vinyl acetate (EVA) and polyolefin elastomer (POE) encapsulant types on the glass-glass (GG) photovoltaic (PV) module reliability. The influence of these two encapsulant types on the reliability of GG modules was compared with baseline glass-polymer backsheet (GB) modules for a benchmarking purpose. Three sets of modules, with four modules in each set, were constructed with two substrates types i.e. glass-glass (GG) and glass- polymer backsheet (GB); and 2 encapsulants types i.e. ethyl vinyl acetate (EVA) and polyolefin elastomer (POE). Each module set was subjected to the following accelerated tests as specified in the International Electrotechnical Commission (IEC) standard and Qualification Plus protocol of NREL: Ultraviolet (UV) 250 kWh/m2; Thermal Cycling (TC) 200 cycles; Damp Heat (DH) 1250 hours. To identify the failure modes and reliability issues of the stressed modules, several module-level non-destructive characterizations were carried out and they include colorimetry, UV-Vis-NIR spectral reflectance, ultraviolet fluorescence (UVF) imaging, electroluminescence (EL) imaging, and infrared (IR) imaging. The above-mentioned characterizations were performed on the front side of the modules both before the stress tests (i.e. pre-stress) and after the stress tests (i.e. post-stress). The UV-250 extended stress results indicated slight changes in the reflectance on the non-cell area of EVA modules probably due to minor adhesion loss at the cell and module edges. From the DH-1250 extended stress tests, significant changes, in both encapsulant types modules, were observed in reflectance and UVF images indicating early stages of delamination. In the case of the TC-200 stress test, practically no changes were observed in all sets of modules. From the above short-term stress tests, it appears although not conclusive at this stage of the analysis, delamination seems to be the only failure mode that could possibly be affecting the module performance, as observed from UV and DH extended stress tests. All these stress tests need to be continued to identify the wear-out failure modes and their impacts on the performance parameters of PV modules. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2020

abstract: The maximum theoretical efficiency of a terrestrial non-concentrated silicon solar cell is 29.4%, as obtained from detailed balance analysis. Over 90% of the current silicon photovoltaics market is based on solar cells with diffused junctions (Al-BSF, PERC, PERL, etc.), which are limited in performance by increased non-radiative recombination in the doped regions. This limitation can be overcome through the use of passivating contacts, which prevent recombination at the absorber interfaces while providing the selectivity to efficiently separate the charge carriers generated in the absorber. This thesis aims at developing an understanding of how the material properties of the contact affect device performance through simulations.The partial specific contact resistance framework developed by Onno et al. aims to link material behavior to device performance specifically at open circuit. In this thesis, the framework is expanded to other operating points of a device, leading to a model for calculating the partial contact resistances at any current flow. The error in calculating these resistances is irrelevant to device performance resulting in an error in calculating fill factor from resistances below 0.1% when the fill factors of the cell are above 70%, i.e., for cells with good passivation and selectivity. Further, silicon heterojunction (SHJ) and tunnel-oxide based solar cells are simulated in 1D finite-difference modeling package AFORS-HET. The effects of material property changes on device performance are investigated using novel contact materials like Al0.8Ga0.2As (hole contact for SHJ) and ITO (electron contact for tunnel-oxide cells). While changing the bandgap and electron affinity of the contact affect the height of the Schottky barrier and hence contact resistivity, increasing the doping of the contact will increase its selectivity. In the case of ITO, the contact needs to have a work function below 4.2 eV to be electron selective, which suggests that other low work function TCOs (like AZO) will be more applicable as alternative dopant-free electron contacts. The AFORS-HET model also shows that buried doped regions arising from boron diffusion in the absorber can damage passivation and decrease the open circuit voltage of the device. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2020

El objetivo de esta tesis es la síntesis de películas delgadas de SnS utilizando técnicas de bajo coste con el fin de fabricar células solares. Nuestra contribución radica en estudiar nuevos materiales susceptibles de ser utilizados para aplicaciones fotovoltaicas, y que puedan ser preparados con técnicas de bajo coste como la técnica de Pyrolysis de Spray Químico (CSP) y caracterizar algunos materiales elegidos para este fin como el Sulfuro de Estaño (SnS). Se han fabricado células solares a partir de la disposición de capas: Mo / SnS / Tampón / i-ZnO / ZnO: Al / Al / Metal. Las capas de buffer serían: In2S3 o CdS. En la primera etapa hemos procedido a la optimización de los parámetros de deposición de películas delgadas de SnS usando la técnica de la CSP, -Variación de la relación [S] / [Sn]. -Variación de la temperatura del substrato. -Variación de la naturaleza del sustrato utilizando sustrato como vidrio, óxido de estaño de indio (ITO) y vidrio recubierto de molibdeno. Las fuentes de productos químicos y disolventes utilizados son: - Cloruro de dihidrato dihidratado para Tin (Sn), Thiourea, Agua destilada como disolvente de la solución, Ethanol (10% de 50mL) con el fin de reducir la tensión superficial del agua que es 72 Nm-1, para permitir la dispersión de la solución depositada sobre el sustrato fácilmente. En una segunda etapa se han dopado pel¿culas delgadas de SnS con algún elemento en la tabla de Mendeleiev para modificar las propiedades f¿sicas y qu¿micas de las pel¿culas. Los elementos químicos utilizados fueron: Plata, Aluminio y Hierro. Se han utilizado varias técnicas de caracterización: - Difracción de rayos X (XRD) para la estructura cristalina de las películas - Espectroscopía Raman para la calidad de las películas - Microscopía electrónica de barrido (SEM) para morfología superficial - Microscopía de Fuerza Atómica (AFM) para topografía de superficie - Análisis dispersivo de energía de rayos X (EDAX) adjunto a SEM para la composición de la película - Espectrofotometría óptica para la transmisión y la determinación del gap - Método de 4 puntas para medición de resistividad del SnS dopado -Mott-Schottky para determinar el tipo de semiconductor y la concentración de portadores Los principales resultados obtenidos en esta tesis pueden resumirse como sigue: -Las películas delgadas mono-sulfuro (SnS) deben depositarse sobre un sustrato de vidrio con [S] / [Sn] igual a una (1) y la temperatura del sustrato igual a 350 ° C para obtener películas densas, bien cubiertas y homogéneas sin agujeros Y grietas. Distancia entre la boquilla al sustrato 25 cm, volumen pulverizado 5 ml, presión de aire 0,7 bar y velocidad de pulverización de 1,5 ml / min. - Para películas dopadas por Plata y Aluminio, todas las películas son estructura ortorrómbica con (111) como pico principal. La intensidad del pico principal aumenta cuando el porcentaje de elemento dopante aumenta en la solución inicial sin ninguna fase secundaria para el dopaje con Al y con Ag8SnS6 y Ag para el dopaje Ag. - El análisis de SEM y AFM demuestra que el elemento dopante Ag no tiene efecto en la morfología y ni en la topografía mientras que el dopaje Al actúa sobre la morfología superficial produciendo una morfología que presenta muchos agujeros para muestras dopadas de 3% a 7%. - EDAX destaca un aumento de Ag en películas cuando la cantidad de Ag aumenta en la solución con S/ Sn¿0,98 cerca de 1 al 5% de porcentaje de dopado de Ag donde como para el dopaje EDAX destaca la mejora de la estequiometría con un aumento del porcentaje de Al Atómica en películas cuando la concentración de Al aumenta en la solución inicial con S / Sn = 0, 99 al 10%. - La resistividad de las muestras dopadas con Ag y Al aumenta con la concentración de dopado y se observa un aumento del gap óptico de 1.66eV a 1.70eV para SnS dopado por Ag y SnS dopado por Al, respectivamente. / ß-In2S3 thin films deposited by Chemical Spray Pyrolysis technique at different substrate temperatures (250 °C-300 °C-350 °C) showed well crystallized thin films with (0 0 12) as preferred direction perpendicular to the plane containing the surface of glass substrate. SEM images showed dense, uniform, well-covered layers that adhere well to substrates and no crack and void space were noted for all substrate temperatures. Microanalysis X confirms the presence of In and S elements with good stoichiometry after vacuum annealing for 30 minutes. Raman spectroscopy analysis confirms ß-In2S3 phase with more prominent modes after vacuum annealing. We also noted a reduction in the gap energies after annealing for films prepared at 250 °C and 350 °C substrate temperatures while for those prepared at 300 °C, the energy of the gap remains stable. Tin mono-sulfide (SnS) thin films must be deposited onto glass substrate with [S]/[Sn] ratio equal to one (1) and substrate temperature equal to 350 °C to obtained dense, well-covered, and homogeneous films without pinholes and cracks. Distance between nozzle to substrate is kept to 25cm, sprayed volume 5mL, air pressure 0.7bar and spray rate 1.5 mL/min. Films doped with Silver (Ag) and Aluminum (Al) were all orthorhombic structure with (111) as main peak. The intensity of main peak increased when the percentage of dopant element increased in the initial solution without any secondary phase for Al-doping films and with Ag8SnS6 and Ag for Ag-doping ones. SEM and AFM analysis showed that Ag-doping element had no effect in the morphology and the topography while Al-doping affected the surface morphology with "fishing net" like morphology with lots of holes for samples doped from 3% to 7%. EDS highlighted an increase of Ag in films when its amount increased in the solution with S/Sn¿0.98 near to 1 at 5% of Ag-doping percentage where as for Al-doping EDS highlighted improvement of stoichiometry with an increase of Al percentage atomic in films when Al concentration increased in the initial solution with S/Sn¿0.99 at 10%. Electrical and energy band gap measurement showed a decrease of resistivity when Ag and Al percentages increased in the solution to reach relatively low resistivity of 108¿.cm and 170¿.cm at 10% for both, and an increased of energy band gap when the Ag and Al-doping elements increased in the solution with 1.66eV and 1.70eV for SnS doped with Ag and SnS doped with Al, respectively. Spray pyrolyzed SnS thin films doped with indium were studied using various optical and electrical techniques. Structural analysis shows that all films crystallize in orthorhombic structure with (111) as a preferential direction without secondary phases. Doping of SnS layers with indium results in better morphology with increased grain size. Absorption measurements indicate dominant direct transition with energy decreasing from around 1.7 eV to 1.5 eV with increased indium supply. Apart from direct transition, an indirect one, of energy of around 1.05 eV, independent on indium doping was identified. The photoluminescence study revealed two donors to acceptor transitions between two deep defect levels and one shallower with energy of around 90 meV. The observed transitions did not depend significantly on In concentration. The conductivity measurements reveal thermal activation of conductivity with energy decreasing from around 165 meV to 145 meV with increased In content. Finally, we were investigated the J-V characteristics of FTO/CdS/SnS,FTO/ZnO/CdS/SnS, FTO/ZnO:Al/CdS/SnS, FTO/ZnO:Al/SnS and FTO/In2S3/SnS solar cells and we found that efficiencies are very low due probably to the recombination at the junction, grain boundaries, etc. / L'objectiu d'aquesta tesi és la síntesi de pel·lícules primes de SnS utilitzant tècniques de baix cost per tal de fabricar cèl·lules solars amb alta eficiència. La nostra contribució rau en estudiar nous materials susceptibles de ser utilitzats per a aplicacions fotovoltaiques, i que puguin ser preparats amb tècniques de baix cost com la tècnica de Spray Piròlisis Químic (CSP) i caracteritzar alguns materials triats per a aquest fi, com ara el Sulfur de estany (SnS). S'han fabricat cèl·lules solars a partir de la disposició de capes: Mo/SnS /Tampó/i-ZnO/ZnO: Al/ Metall. Les capes de per al bufer intermèdi has sigut de In2S3 i CdS. En la primera etapa hem procedit a l'optimització dels paràmetres de deposició de pel·lícules primes de SnS usant la tècnica CSP. -Variació de la relació [S] / [Sn]. -Variació de la temperatura Ts del substrat. -Variació de la naturalesa del substrat utilitzant substrat com: vidre simple, òxid d'estany d'indi (ITO) i vidre recobert de molibdè. Les fonts de productes químics i dissolvents utilitzats han sigut; Clorur d'estany per a l'estany (Sn), thiourea per sofre (S). Aigua destil·lada com a dissolvent de la solució. Ethanol (10% de 50ml) per tal de reduir la tensió superficial de l'aigua que és 72 Nm-1, per a permetre la dispersió de la solució dipositada fàcilment sobre el substrat. En una segona etapa s'han dopat pel.lícules primes de SnS amb algun element en la taula de Mendeleiev per modificar les propietats físiques i químiques de les pel.l¿cules. Els elements químics utilitzats són: Plata (Ag+), alumini (Al3+), Ferro (Fe2+), Coure (Cu2+) i Antimoni (SB3+) com a font de nitrat de plata (AgNO3), Clorur d'alumini (AlCl3) (FeCl2·4H2O ), Clorur de Coure (CuCl2 i Clorur de Antimoni (SbCl3). S'han utilitzat diverses tècniques de caracterització: - Difracció de raigs X (XRD) per a l'estructura de les pel·lícules i cristal - Raman Spectroscopy per a la qualitat de les pel·lícules - Microscòpia electrònica de rastreig (SEM) per morfologia superficial - Microscòpia de Força Atòmica (AFM) per topografia de superfície - Anàlisi dispersiu d'energia de raigs X (EDAX) adjunt a SEM per a la composició de la pel·lícula -Espectrofotometría per a la transmissió i el mesurament de la banda d'energia utilitzant la trama de Tauc - Tècnica de punta-sonda per a mesurament de resistivitat amb dopat SnS -Mott-Schottky per determinar el tipus de semiconductor i la concentració de portadors Els principals resultats obtinguts en aquesta tesi poden resumir així: -Les pel·lícules primes mico-sulfur (SnS) han de dipositar-sobre un substrat de vidre amb [S]/[Sn] igual a una (1) i la temperatura del substrat igual a 350 °C per obtenir pel·lícules denses, ben cobertes i homogènies sense forats I esquerdes. Distància entre el filtre al substrat 25 cm, volum polvoritzat 5 ml, pressió d'aire 0,7 bar i velocitat de polvorització de 1,5 ml / min. Per pel·lícules dopades per Plata i alumini, totes les pel·lícules són estructura ortorrómbica amb (111) com pic principal. La intensitat del pic principal augmenta quan el percentatge d'element dopant augmenta en la solució inicial sense cap fase secundària per al dopatge amb Al i amb Ag8SnS6 i Ag per al dopatge Ag. L'anàlisi de SEM i AFM demostra que l'element dopant Ag no té efecte en la morfologia i la topografia mentre que el dopatge en actua sobre la morfologia superficial produint una morfologia que presenta molts forats per a mostres dopades de 3% a 7%. EDAX destaca un augment de Ag en pel·lícules quan la quantitat d'Ag augmenta en la solució amb S / Sn¿0,98 prop d'1 a 5% de percentatge de dopatge d'Ag on com per al dopatge EDAX destaca la millora de l'estequiometria amb un augment del percentatge d'al Atòmica en pel·lícules quan la concentració d'al augmenta en la solució inicial amb S / Sn = 0,99 al 10%. / Sall, T. (2017). Preparation and Characterization of SnS thin films by Chemical Spray Pyrolysis for fabrication of solar cells [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/95412 / TESIS

Harnessing the Sun’s energy via the conversion of solar photons to electricity has emerged as a sustainable energy source to fulfill our future demands. In this regard, solution-processable, size-tunable PbS quantum dots (QDs) have been identified as a promising active materials for photovoltaics (PVs). Yet, there are still serious challenges that hinder the full exploitation of QD materials in PVs. This dissertation addresses two main challenges to aid these QDs in fulfilling their tremendous potential in PV applications. First, it is essential to establish a large-scale synthetic technique which maintains control over the reaction parameters to yield QDs with well-defined shape, size, and composition. Rigorous protocols for cost-effective production on a scale are still missing from literature. Particularly, previous reports of record-performance QD-PVs have been based on small-scale, manual, batch syntheses. One way to achieve a controlled large-scale synthesis is by reducing the reaction volume to ensure uniformity. Accordingly, we design a droplet-based continuous-flow synthesis of PbS QDs. Only upon separating the nucleation and growth phases, via a dual-temperature-stage reactor, it was possible to achieve high-quality QDs with high photoluminescence quantum yield (50%) in large-scale. The performance of these QDs in a PV device was comparable to batch-synthesized QDs, thus providing a promise in utilizing automated synthesis of QDs for PV applications. Second, it is crucial to study and control the charge transfer (CT) dynamics at QD interfaces in order to optimize their PV performance. Yet, the CT investigations based on PbS QDs are limited in literature. Here, we investigate the CT and charge separation (CS) at size-tunable PbS QDs and organic acceptor interfaces using a combination of femtosecond broadband transient spectroscopic techniques and steady-state measurements. The results reveal that the energy band alignment, tuned by the quantum confinement, is a key element for efficient CT and CS processes. Additionally, the presence of interfacial electrostatic interaction between the QDs and the acceptors facilitates CT from large PbS QD (bandgap < 1 eV); thus enabling light-harvesting from the broad near-infrared solar spectrum range. The advances in this work – from automated synthesis to charge transfer studies – pave new pathways towards energy harvesting from solution-processed nanomaterials.

Photovoltaics provide a feasible route to fulfilling the substantial increase in demand for energy worldwide. Solution processable organic photovoltaics (OPVs) have attracted attention in the last decade because of the promise of low-cost manufacturing of sufficiently efficient devices at high throughput on large-area rigid or flexible substrates with potentially low energy and carbon footprints. In OPVs, the photoactive layer is made of a bulk heterojunction (BHJ) layer and is typically composed of a blend of an electron-donating (D) and an electron-accepting (A) materials which phase separate at the nanoscale and form a heterojunction at the D-A interface that plays a crucial role in the generation of charges. Despite the tremendous progress that has been made in increasing the efficiency of organic photovoltaics over the last few years, with power conversion efficiency increasing from 8% to 13% over the duration of this PhD dissertation, there have been numerous debates on the mechanisms of formation of the crucial BHJ layer and few clues about how to successfully transfer these lessons to scalable processes. This stems in large part from a lack of understanding of how BHJ layers form from solution. This lack of understanding makes it challenging to design BHJs and to control their formation in laboratory-based processes, such as spin-coating, let alone their successful transfer to scalable processes required for the manufacturing of organic solar cells. Consequently, the OPV community has in recent years sought out to better understand the key characteristics of state of the art lab-based organic solar cells and made efforts to shed light on how the BHJ forms in laboratory-based processes as well as in scalable processes. We take the view that understanding the formation of the solution-processed bulk heterojunction (BHJ) photoactive layer, where crucial photovoltaic processes take place, is the one of the most crucial steps to developing strategies towards the implementation of organic solar cells with high efficiency and manufacturability. In this dissertation, we investigate the mechanism of the BHJ layer formation during solution processing from common lab-based processes, such as spin-coating, with the aim of understanding the roles of materials, formulations and processing conditions and subsequently using this insight to enable the scalable manufacturing of high efficiency organic solar cells by such methods as wire-bar coating and blade-coating. To do so, we have developed state-of-the-art in situ diagnostics techniques to provide us with insight into the thin film formation process. As a first step, we have developed a modified spin-coater which allows us to perform in situ UV-visible absorption measurements during spin coating and provides key insight into the formation and evolution of polymer aggregates in solution and during the transformation to the solid state. Using this method, we have investigated the formation of organic BHJs made of a blend of poly (3-hexylthiophene) (P3HT) and fullerene, reference materials in the organic solar cell field. We show that process kinetics directly influence the microstructure and morphology of the bulk heterojunction, highlighting the value of in situ measurements. We have investigated the influence of crystallization dynamics of a wide-range of small-molecule donors and their solidification pathways on the processing routes needed for attaining high-performance solar cells. The study revealed the reason behind the need of empirically-adopted processing strategies such as solvent additives or alternatively thermal or solvent vapor annealing for achieving optimal performance. The study has provided a new perspective to materials design linking the need for solvent additives or annealing to the ease of crystallization of small-molecule donors and the presence or absence of transient phases before crystallization. From there, we have extended our investigation to small-molecule (p-DTS (FBTTh2)2) fullerene blend solar cells, where we have revealed new insight into the crucial role of solvent additives. Our work has also touched upon modern polymers, such as PBDTTPD, where we have found the choice of additives impacts the formation mechanism of the BHJ. Finally, we have performed a comparative study of the BHJ film formation dynamics during spin coating versus wire-bar coating of p-DTS(FBTTh2)2: fullerene blends that has helped in curbing the performance gap between lab-based and scalable techniques. This was done by implementing a new apparatus that combines the benefits of rapid thin film drying common to spin coating with scalability of wire-bar coating. Using the new apparatus, we successfully attain similar performance of solar cell devices to the ones fabricated by spin coating with dramatically reduced material waste.

Organic photovoltaics (OPVs) have received tremendous attention in recent years due to their numerous attractive attributes such as, the potential for high power conversion efficiency (PCE), mechanical flexibility, and the potential for large-scale manufacturing via low-cost techniques. To date, the record PCE values for bulk-heterojunction (BHJ) OPVs exceed 18% for single-junction cells thanks to the rapid development of donors and acceptors materials for active layer. However, the progress of hole-transporting layer (HTL) systems, which is a key device component to reduce the additional performance losses of OPVs, has been limited with only a handful of materials available like PEDOT:PSS and MoOX. In this thesis, I introduce serval materials to unitize as hole-selective contact in high-performance OPVs. Firstly, the application of liquid-exfoliated two-dimensional transition metal disulfides (TMDs) is demonstrated as the HTLs in OPVs. The solution processing of few-layer WS2 suspensions was directly spun onto transparent indium-tin-oxide (ITO) electrodes yield solar cells with superior power conversion efficiency (PCE), improved fill-factor (FF), enhanced short-circuit current (JSC), and lower series resistance than devices based on PEDOT:PSS. Based on PM6:Y6:PC71BM BHJ layer, the cells with WS2 HTL exhibit the highest PCE of 17% thanks to the favorable photonic structure and reduced bimolecular recombination losses in WS2-based cells. Next, the self-assembled monolayer (SAM) namely 2PACz is utilized as hole-selective contact directly onto the ITO anode. The 2PACz modifies the work function of ITO while simultaneously affecting the BHJ layer’s morphology deposited atop. This ITO-2PACz anode is utilized in OPV with PM6:BTP-eC9:PC71BM, showing a remarkable PCE of 18.0%. The enhanced performance is attributed to reduced contact-resistance, lower bimolecular recombination losses, and improved charge transport within the BHJ layer. Lastly, the previously 2PACz SAM was functionalized with bromide functional groups, namely Br-2PACz, which is investigated as hole-extracting interlayers in OPVs. The highest occupied molecular orbital (HOMO) energy of Br-2PACz was measured at -6.01 eV, and significant changes the work function of ITO electrodes upon chemical functionalization. OPV cells based on PM6:BTP-eC9:PC71BM using ITO/Br-2PACz anodes exhibit a maximum PCE of 18.4%, outperforming devices with ITO/PEDOT:PSS (17.5%), resulting from lower interface resistance, improved hole transport, and longer carrier lifetimes.

This work studies the subject of perovskite solar cells. The structure of perovskites is described along with a portion of photovoltaics history that led to the employment of perovskites as absorpsion layers. Further, methods of measurement for solar cells such as impedance spectroscopy, photospectroscopy and load characteristics are summarized. Lastly there is a description of already done analytics of perovskite solar cells with the summary of the results. In the practical part, there are measurements made to find out any effect of cell topology or light source wavelength on the cell performance.

Organická elektronika je dynamické, rychle se rozvíjející odvětví. Studium nových materiálů pro organickou elektroniku je důležitým úkolem jak z hlediska výkonnosti budoucích zařízení a ekonomičnosti procesů, tak z hlediska vlivu jejich používání na životní prostředí. Deriváty diketopyrrolopyrrolu patří mezi zajímavé materiály, které jsou v posledních letech studovány s ohledem na využití v organické elektronice. Dizertační práce je zaměřena na studium těchto materiálů a jejich jak optickou, tak i elektrickou charakterizaci. Součástí je také zhodnocení jejich potenciální aplikace v organické elektronice a návrhy optimalizace jejich výkonu. Teoretická část práce popisuje současný stav na poli organické elektroniky zaměřený na materiály na bázi diketopyrrolopyrrolu. Následující výsledková část shrnuje podstatné výsledky práce a obsahuje stručný úvod k přiloženým publikacím, včetně zhodnocení vlastního přínosu autora k jednotlivým publikacím. Výsledková část dále sestává z 6 vědeckých publikací, které jsou nedílnou součástí této práce a jsou tematicky propojeny v oblasti organické elektroniky, nových materiálů na bázi diketopyrrolopyrrolu a jejich aplikací. Z formálního hlediska je práce na základě čl. 42 odstavce 1b Studijního a zkušebního řádu VUT koncipovaná jako tematicky uspořádaný soubor uveřejněných prací a prací přijatých k publikaci.