Preparation And Optimization Of Planar Heterojunction Perovskite Solar Cells By Solvent Engineering

Over the past several years,perovskite solar cells(PSCs)have attracted great attention due to their facile fabrication process,low cost,high power conversion efficiency(PCE).The quality of the perovskite layer plays a crucial role in determining the PCE of the PSCs.However,the quality of the perovskite films prepared by the conventional solution methods is poor and the cell performance is low.In this thesis,the preparation methods of the perovskite layers with solvent engineering were studied systematically for the fabrication of planar heterojunction PSCs.The quality of the perovskite films and the performance of the PSCs were improved remarkable by solvent engineering.The main contents of the thesis are as follows:1.Optimization of spin coating-impregnation process based on solvent engineering for preparation of perovskite filmsThe perovskite films were prepared by solvent engineering,in which the Pb I2(DMSO)precursor films were spin-coated by using DMF-DMSO mixed solvent,and the conversion of precursor to perovskite was improved effectively compared with the PbI2 precursor films.As a result,the average PCE of PSCs increased from 1.43% to 4.39%.After optimizing the concentration of precursor solution,the average PCE of PSCs increased further to 5.54%,and the PCE of the best device reached 9.50%.Although the solvent engineering promoted the conversion of precursor,the perovskite films prepared by spin coating-impregnation method still showed porous morphology,which restricted the performance of planar heterojunction PSCs.2.Optimization of two-step spin coating process based on solvent engineering for preparation of perovskite filmsIn order to solve the problems aforementioned,the perovskite film was prepared by two-step spin coating method,which is more suitable for planar devices.In addition to using DMF-DMSO mixed solvent to improve the conversion of precursor,the spin-coating speed and precursor concentrations were optimized for the two-step spin coating method,resulting in the compact perovskite film with large particle size.The average PCE of the devices fabricated under the optimized conditions was 10.8%,and the PCE of the best device reached 12.75%.3.Optimization of one-step spin coating process based on solvent engineering for preparation of perovskite filmsIn comparison with the two-step method,the one-step method has the advantages of less steps,high precursor conversion and suitable for the preparation of mixed perovskite films.However,perovskite films prepared by the conventional one-step spin coating show poor quality.In this thesis,environmental-friendly 2-butanol was used as an anti-solvent to assist the film formation process of the perovskite.The precursor concentration and the ratio of precursors were optimized.The average PCE of the devices fabricated under the optimized conditions was 9.81%,and the PCE of the best device was 11.3%.4.Preparation of flexible PSCs by two-step spin coating method based on solvent engineeringCompared with the traditional rigid solar cells,flexible solar cells have the advantages of low cost,light weight,bendable,and find wide applications in a number of diverse areas.The whole fabrication process of PSCs used in this thesis is below 150°C,and thus very suitable for the fabrication of flexible PSCs.The two-step spin-coating method was used to fabricate the PSCs on ITO/PET flexible substrates under optimized conditions,and the PCE of 6.1% was achieved for the flexible PSCs.