Fabrication Of Flexible Perovskite Solar Cells Based On SnO₂ Electron Transport Layer

Flexible solar cells have attracted extensive attention from academia and industry because of their potential applications in many fields,such as architecture,transportation,portable and wearable electronics.In recent years,perovskite solar cells?PSCs?have become one of the most promising photovoltaic technologies,which not only possess high energy conversion efficiency and low manufacturing cost,but also low temperature?<150??solution processibility,and thus are suitable for the application for high efficiency flexible solar cells.At present,rigid PSCs have achieved high efficiencies,but the performance of flexible devices is far behind them.In order to achieve high-efficiency flexible planar PSCs,it is crucial to prepare high-quality charge extraction layers at low temperature on the flexible substrates.In this thesis,we adopt tin oxide?SnO₂?as electron transport materials?ETLs?due to its high electron mobility and low-temperature solution processability.To study the effect of SnO₂ synthesized by different methods on the performance of flexible devices,as well as to study the fabrication of high-efficiency flexible PSCs and modules,the main research contents and conclusions are as follows:1.Sol-gel method has been used to directly prepare SnO₂ ETLs at low temperature,and it is found that the quality of the SnO₂ films is greatly affected by environmental humidity,reducing the performance and reproducibility of the devices.Through analyzing,we find that the environmental humidity would affect the hydrolysis of SnCl₄,resulting in unreacted SnCl₄ residuals on the surface of SnO₂ films,and affecting the photogenerated electrons transporting from perovskite to SnO₂ ETLs.Therefore,we have developed a simple water bath post-treatment,which could allow SnCl₄ to be completely hydrolyzed without suffering from the effect of environmental humidity,achieving highly crystalline SnO₂ films,and enhancing charge extraction and transport at the interface.The performance of PSCs has been significantly improved based on the water bath post-treatment of SnO₂ thin films,with the champion power conversion efficiency?PCE?up to 19.17%,which is much higher than that of untreated devices?17.59%?.More importantly,since the quality of SnO₂ thin films prepared by this method is not affected by environmental humidity,the devices reproducibility has been greatly improved.The efficiency of flexible devices fabricated by this method can achieve 12.78%.2.The SnO₂ thin films prepared by sol-gel method have many defects.Although the performance has been improved after water treatment,the efficiency of flexible SnO₂-based device is still unsatisfactory.In order to further optimize the quality of SnO₂ ETLs,we have synthesized the SnO₂ nanoparticles by heating the SnCl₄·5H₂O aqueous solution at 90?.By adjusting the concentration and hydrolysis time of SnCl4·5H2O aqueous solution,the self-releasing acid assisted hydrolysis of SnCl4 can be controlled to achieve uniform SnO₂ nanoparticles?SnO₂ NPs?.The pre-crystallized SnO₂ NPs has high crystallinity,few defects and high electron mobility,with further optimization of PCBM at interface,the PCE of the prepared flexible devices is improved to 15.56%.3.The problem in devices scaling up must be solved for the real application of flexible devices.In general,when the device size is enlarged,its efficiency will be greatly reduced.The main problem lies in the quality control of the high uniformity large-area films of the functional layers.Here,we have developed a fabrication technique to print large-area SnO₂ dense films for the flexible PSMs.We have made the pre-crystallized SnO₂ nanoparticles into ink,printed large-area SnO₂ ETLs by the scalable slot-die coating technology,and deposited perovskite layers by one-step solvent engineering method to realize the preparation of large-area flexible devices.Eventually,the flexible perovskite solar module made from the printed SnO₂ film is connected by 6 sub-cells in series with an effective area of 16.07 cm²,and achieves the highest PCE of 15%.