Application Of Ionic Liquids In Efficient And Stable Perovskite Solar Cells

In the last decade,the efficiency of perovskite solar cells has increased rapidly from 3.8%to 25.7%,showing great potential for replacing silicon solar cells and future commercial applications.Although the efficiency of perovskite solar cells is comparable to that of silicon solar cells,perovskite solar cells still have two problems to be solved:stability and large-area fabrication.Therefore,we use ionic liquid to optimize the perovskite solar cells,aiming to improve its efficiency and stability.We characterize the effect of ionic liquid interface modification and investigate the mechanism of ionic liquid as dopant for hole transport material,and finally verify the feasibility of large-area fabrication.The main research contents of this paper are as follows:(1)We investigated the effect of BMPIP-TFSI ionic liquid to be used as interface modification material.BMPIP-TFSI can effectively passivate perovskite surface.The hydrophobicity of BMPIP-TFSI can also protect the perovskite film from water and oxygen erosion.However,the performance of devices based on ionic liquid as interface modification material did not improve significantly.We analyzed the origin of its failure and found that when spin-coating the hole transport layer,the ionic liquid will be dissolved,resulting in a greatly reduced passivation effect.(2)We replaced Li-TFSI with BMPIP-TFSI,the latter was used as the dopant for the hole transport material.This strategy can solve the problem induced by BMPIP-TFSI interface modification.BMPIP-TFSI serves as a p-type dopant which can improve the hole mobility and conductivity of the hole transport layer.It can also adjust the energy level alignment.Its hydrophobicity improved the ability of the device to withstand water and oxygen erosion.Finally,we fabricated a batch of devices with the highest efficiency reaches 23.01%.The open-circuit voltage increased from 1.12 V to 1.17 V.The un-encapsulated devices can maintain 85%of its initial efficiency after 500 h stored in humid environment.(3)We further verified the feasibility of large-area fabrication of BMPIP-TFSI as dopant for hole transport layer.A 5×5cm~2device was fabricated.We compared the effect of spin coating and blade coating on the optical properties and surface morphology of the film.The spin-coating method is more suitable for the fabrication of small cells.When it comes to module fabrication,the spin coating method will lead to non-uniform film.The blade coating method can be used to solve this problem,and the highest efficiency of the device fabricated by the blade coating method is 16.73%.