• Energy Research

Abstract Dye-sensitized solar cells (DSCs) have a typical sandwich structure, with the active layers between two conductive glass sheets. Their co-planarity could be an issue in the mass production of large area devices. The micrometric gap should be uniform all over the device, in order to maintain a good electrolyte layer. The frames of sealant, which isolate the adjacent cells in a module, usually work also as spacers. Nevertheless, the uniformity of the gap is not commonly tested in a systematic way. Here large area empty blanks and full DSCs were studied by means of optical interferometry, i.e., monochromatic surface scan and wavelength scan. The collected fringe patterns allowed retrieval of the microchamber’s absolute profile. In some cases, evident U-shaped bending was found, with edge-to-center variation up to Δ h / h ≈ 80%. Interestingly, despite the large absorption and the weak index contrast in the full DSCs, a good fringes’ visibility was achieved, by adopting near-infrared (IR) laser source and filtering off external reflections. Moreover, the IR n and k indexes of porous titania dyed and filled with electrolyte were retrieved. In summary, the results show that the bending effect must always be tackled for large area, by using the right sealing frames and thermal treatments. Further improved IR interferometry can be successfully implemented for in-line testing of DSCs structure and uniformity.

Over the past few years, dye-sensitized solar cell (DSC) research has been focused on the material and process cost reduction, and on the electronics integration of the devices. Monolithic design is one of the most promising DSC architectures for mass production, because it allows the elimination of one conductive substrate and offers the possibility of printing layer-by-layer the materials that compose the structure. In this study, the formulation, the realization, and the processing of the spacer and the catalyst layers are proposed, and the relative performance in terms of J-V characteristics, incident photon to current conversion efficiency, and impedance analysis of the device with the optimized material thickness is reported. The optimized profile of the overall structure permits us to obtain masked cells with a conversion efficiency of about 5% with no chemical treatment.

Les couches de transport d'électrons (ETL) jouent un rôle fondamental dans les cellules solaires à pérovskite (PSC) grâce à l'extraction de charge. Ici, nous avons développé des ESP flexibles sur 12 types différents d'ETL basés sur SnO2. Nous montrons que les ETL doivent être spécifiquement développés pour les substrats en plastique afin d'atteindre 15% de cellules flexibles efficaces. Les recettes développées pour les substrats en verre ne transfèrent généralement pas directement. Parmi tous les ETL, les doubles couches de ZnO/SnO2 ont fourni le rendement moyen de conversion de puissance le plus élevé de 14,6 % (meilleure cellule 14,8 %), soit 39 % de plus que celui des cellules flexibles du même lot basées sur des ETL uniquement de SnO2. Cependant, les cellules avec un seul ETL constitué de nanoparticules de SnO2 se sont avérées plus stables ainsi que plus efficaces et reproductibles que le SnO2 formé à partir d'un précurseur liquide (SnO2-LP). Nous avons cherché à mieux comprendre ce qui fait un bon ETL sur les substrats en polyéthylène téréphtalate (PET). Plus que d'assurer le transport d'électrons (comme le montrent les analyses de résistance en courant et en série), fournir des résistances de shunt élevées (RSH) et des courants de recombinaison plus faibles (Ioff) est essentiel pour obtenir une efficacité élevée. En fait, le RSH des ESP fabriqués sur verre était deux fois plus grand, et Ioff était de 76 % inférieur en termes relatifs, en moyenne, à ceux sur PET, indiquant un comportement de blocage considérablement meilleur des ETL sur verre, ce qui explique dans une large mesure les différences de pce moyen (+29 % en termes relatifs pour le verre par rapport au PET) entre ces deux types d'appareils. Il est important de noter que nous avons également constaté une tendance claire pour tous les ETL et pour différents substrats entre le comportement de mouillage de chaque surface et les performances finales du dispositif, les efficacités augmentant avec des angles de contact plus faibles (compris entre ∼50 et 80°). Un meilleur mouillage, avec des angles de contact moyens inférieurs de 25% sur le verre par rapport au PET, était propice à la fourniture de couches et d'interfaces de meilleure qualité. Cette connaissance peut aider à optimiser davantage les appareils flexibles et à combler l'écart d'efficacité qui existe encore avec leurs homologues en verre. Las capas de transporte de electrones (ETL) desempeñan un papel fundamental en las células solares de perovskita (PSC) a través de la extracción de carga. Aquí, desarrollamos PSC flexibles en 12 tipos diferentes de ETL basados en SnO2. Mostramos que los ETL deben desarrollarse específicamente para sustratos de plástico para lograr células flexibles con un 15% de eficiencia. Las recetas desarrolladas para sustratos de vidrio no suelen transferirse directamente. Entre todos los ETL, las capas dobles de ZnO/SnO2 entregaron la mayor eficiencia de conversión de potencia promedio del 14.6% (mejor celda 14.8%), 39% más alta que la de las celdas flexibles del mismo lote basadas en ETL solo de SnO2. Sin embargo, se encontró que las células con un solo ETL hecho de nanopartículas de SnO2 eran más estables, así como más eficientes y reproducibles que el SnO2 formado a partir de un precursor líquido (SnO2-LP). Nuestro objetivo era aumentar la comprensión de lo que hace un buen ETL en sustratos de tereftalato de polietileno (PET). Más que garantizar el transporte de electrones (como se ve en el análisis de resistencia en corriente y en serie), la entrega de altas resistencias de derivación (RSH) y corrientes de recombinación más bajas (Ioff) es clave para obtener una alta eficiencia. De hecho, el RSH de las PSC fabricadas en vidrio fue el doble de grande, y el Ioff fue un 76% menor en términos relativos, en promedio, que los de PET, lo que indica un comportamiento de bloqueo considerablemente mejor de los ETL en vidrio, lo que explica en gran medida las diferencias en el PCE promedio (+29% en términos relativos para vidrio frente a PET) entre estos dos tipos de dispositivos. Es importante destacar que también encontramos una tendencia clara para todos los ETL y para diferentes sustratos entre el comportamiento de humectación de cada superficie y el rendimiento final del dispositivo, con eficiencias que aumentan con ángulos de contacto más bajos (que oscilan entre ~50 y 80°). Una mejor humectación, con ángulos de contacto medios inferiores en un 25% en el vidrio en comparación con el PET, fue propicia para ofrecer capas e interfaces de mayor calidad. Este conocimiento puede ayudar a optimizar aún más los dispositivos flexibles y cerrar la brecha de eficiencia que todavía existe con sus contrapartes de vidrio. Electron transport layers (ETLs) play a fundamental role in perovskite solar cells (PSCs) through charge extraction. Here, we developed flexible PSCs on 12 different kinds of ETLs based on SnO2. We show that ETLs need to be specifically developed for plastic substrates in order to attain 15% efficient flexible cells. Recipes developed for glass substrates do not typically transfer directly. Among all the ETLs, ZnO/SnO2 double layers delivered the highest average power conversion efficiency of 14.6% (best cell 14.8%), 39% higher than that of flexible cells of the same batch based on SnO2-only ETLs. However, the cells with a single ETL made of SnO2 nanoparticles were found to be more stable as well as more efficient and reproducible than SnO2 formed from a liquid precursor (SnO2-LP). We aimed at increasing the understanding of what makes a good ETL on polyethylene terephthalate (PET) substrates. More so than ensuring electron transport (as seen from on-current and series resistance analysis), delivering high shunt resistances (RSH) and lower recombination currents (Ioff) is key to obtain high efficiency. In fact, RSH of PSCs fabricated on glass was twice as large, and Ioff was 76% lower in relative terms, on average, than those on PET, indicating considerably better blocking behavior of ETLs on glass, which to a large extent explains the differences in average PCE (+29% in relative terms for glass vs PET) between these two types of devices. Importantly, we also found a clear trend for all ETLs and for different substrates between the wetting behavior of each surface and the final performance of the device, with efficiencies increasing with lower contact angles (ranging between ∼50 and 80°). Better wetting, with average contact angles being lower by 25% on glass versus PET, was conducive to delivering higher-quality layers and interfaces. This cognizance can help further optimize flexible devices and close the efficiency gap that still exists with their glass counterparts. تلعب طبقات نقل الإلكترون (ETLs) دورًا أساسيًا في الخلايا الشمسية البيروفسكية (PSCs) من خلال استخراج الشحنة. هنا، قمنا بتطوير PSCs مرنة على 12 نوعًا مختلفًا من ETLs بناءً على SnO2. نظهر أن ETLs تحتاج إلى تطوير خصيصًا للركائز البلاستيكية من أجل تحقيق خلايا مرنة فعالة بنسبة 15 ٪. لا تنتقل الوصفات المطورة للركائز الزجاجية عادة مباشرة. من بين جميع ETLs، قدمت الطبقات المزدوجة ZnO/SnO2 أعلى متوسط لكفاءة تحويل الطاقة بنسبة 14.6 ٪ (أفضل خلية 14.8 ٪)، أعلى بنسبة 39 ٪ من الخلايا المرنة من نفس الدفعة بناءً على ETLs SnO2 فقط. ومع ذلك، وجد أن الخلايا التي تحتوي على ETL واحد مصنوع من جزيئات SnO2 النانوية أكثر استقرارًا وكذلك أكثر كفاءة وقابلية للتكاثر من SnO2 المتكون من سلائف سائلة (SnO2 - LP). كنا نهدف إلى زيادة فهم ما يجعل ETL جيدًا على ركائز البولي إيثيلين تيريفثالات (PET). أكثر من ضمان نقل الإلكترون (كما يتضح من تحليل مقاومة التيار المستمر والمقاومة التسلسلية)، فإن توفير مقاومات تحويلة عالية (RSH) وتيارات إعادة التركيب المنخفضة (Ioff) هو المفتاح للحصول على كفاءة عالية. في الواقع، كان RSH من PSCs المصنعة على الزجاج أكبر بمرتين، وكان Ioff أقل بنسبة 76 ٪ من الناحية النسبية، في المتوسط، من تلك الموجودة على PET، مما يشير إلى سلوك حجب أفضل بكثير لـ ETLs على الزجاج، مما يفسر إلى حد كبير الاختلافات في متوسط PCE (+29 ٪ من الناحية النسبية للزجاج مقابل PET) بين هذين النوعين من الأجهزة. الأهم من ذلك، وجدنا أيضًا اتجاهًا واضحًا لجميع ETLs وللركائز المختلفة بين سلوك الترطيب لكل سطح والأداء النهائي للجهاز، مع زيادة الكفاءة مع انخفاض زوايا التلامس (تتراوح بين 50 و 80درجة). كان الترطيب الأفضل، مع انخفاض متوسط زوايا التلامس بنسبة 25 ٪ على الزجاج مقابل البولي إيثيلين تيرفثالات، مواتياً لتقديم طبقات وواجهات عالية الجودة. يمكن أن يساعد هذا الإدراك في تحسين الأجهزة المرنة بشكل أكبر وسد فجوة الكفاءة التي لا تزال موجودة مع نظيراتها الزجاجية.

AbstractDye‐sensitized and perovskite solar cells have seen tremendous efforts in their development in recent years. Amongst these developments are the design and implementation of fabrication techniques that can guarantee high performance as well as scalability over large areas. Laser processing has become a versatile and important tool in many industries and has also been applied successfully to both types of solar cell technologies, culminating in the demonstration of dye solar devices where all temperature treatments have been replaced with laser techniques, and of high‐performance solid‐state perovskite modules. Herein, we introduce concepts and review the available literature, pertaining to the effective utilization of laser beams for the development of both dye‐sensitized and perovskite photovoltaic technologies.

In this work we present a transparent conductive oxide (TCO)-free flexible perovskite planar heterojunction solar cell made with a semitransparent anode realized with a highly conductive poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) PEDOT:PSS (PH1000 by Clevios) modified with ethylene glycol layer, deposited via spray coating. We investigated several formulations of PEDOT:PSS modified by addition of solvents with high boiling point such as ethylene glycol (EG) and dimethyl sulfoxide (DMSO). Optimized samples show a 65% transmittance at 550 nm and a sheet resistance of 28 Omega/square. On these optimized electrodes we fabricated a TCO-free flexible device, the best of which exhibited a power conversion efficiency of 4.9% under 100 mW/cm(2) illumination at AM1.5G. The efficiency of the perovskite planar-heterojunction solar cell, with the modified PEDOT:PSS anode was comparable to the one realized on a PET-ITO anode. Moreover, in the bending test, ITO-free flexible solar cell manifested superior mechanical robustness, showing the high flexibility of the perovskite layer. (C) 2015 Elsevier B.V. All rights reserved.

Perovskite solar cells employing CH3NH3PbI3-xClx active layers show power conversion efficiency (PCE) as high as 20% in single cells and 13% in large area modules. However, their operational stability has often been limited due to degradation of the CH3NH3PbI3-xClx active layer. Here, we report a perovskite solar module (PSM, best and av. PCE 10.5 and 8.1%), employing solution-grown TiO2 nanorods (NRs) as the electron transport layer, which showed an increase in performance (∼5%) even after shelf-life investigation for 2500 h. A crucial issue on the module fabrication was the patterning of the TiO2 NRs, which was solved by interfacial engineering during the growth process and using an optimized laser pulse for patterning. A shelf-life comparison with PSMs built on TiO2 nanoparticles (NPs, best and av. PCE 7.9 and 5.5%) of similar thickness and on a compact TiO2 layer (CL, best and av. PCE 5.8 and 4.9%) shows, in contrast to that observed for NR PSMs, that PCE in NPs and CL PSMs dropped by ∼50 and ∼90%, respectively. This is due to the fact that the CH3NH3PbI3-xClx active layer shows superior phase stability when incorporated in devices with TiO2 NR scaffolds.

Most laboratories employ spin coating with application of antisolvent to achieve high efficiency in perovskite solar cells. However, this method wastes a lot of material and is not industrially usable. Conversely, large area coating techniques such as blade and slot-die require high precision engineering both for deposition of ink and for gas or for electromagnetic drying procedures that replace, out of necessity, anti-solvent engineering. Here we present a simple and effective method to deposit uniform high-quality perovskite films with a piece of paper as an applicator at low temperatures. We fabricated solar cells on flexible PET substrates manually with 11% power conversion efficiency. Deposition after soaking the sheet of paper in a green antisolvent improved the efficiency by 82% compared to when using dry paper as applicator. This new technique enables manual film deposition without any expensive equipment and has the potential to be fully automated for future optimization and exploitation.