Fabrication Of FA-based Perovskite Solar Cells And Modules Via Two-step Sequential Deposition Method

In recent years,perovskite solar cells（PSCs）have developed rapidly,and the certified power conversion efficiency（PCE）has reached 25.7%,and it still maintains the trend of continuous breakthroughs,showing great commercial application prospects.However,currently reported high-performance device fabrication processes focus on spin-coating.And it is necessary to use various strategies such as anti-solvent to prepare high-quality perovskite films.In fact,spin-coating shows great advantages in the study of nucleation and crystallization mechanism and the preparation of small-area devices,but the optoelectronic properties of large-area perovskite components will greatly decrease.Therefore,a process that can fabricate high-quality perovskite thin films on a large area is currently the top priority in accelerating the commercialization of PSCs.In the existing research,the blade coating method is a preparation process with simple operation and high material utilization,and is considered by researchers as an effective method for preparing large-area thin films.For the blade coating process,the quality of perovskite films can be effectively improved by changing the precursor solution composition or solvent engineering.Therefore,a lot of research has focused on the preparation of methylamine（MA）-based perovskite functional layers by one-step blade coating,but less research has been done on formamidine（FA）-based perovskites with better stability and performance.The main reason is that the one-step blade coating method has low repeatability and is difficult to control the nucleation and growth process of FA-based perovskites.In contrast,the two-step sequential blade-coating deposition method exhibits advantages.The interaction process between lead halide and organic amine salt effectively solves the problem of uncontrollable one-step nucleation process of FA-based perovskites.Therefore,the two-step sequential blade coating method is a more controllable and reliable method for preparing thin films uniformly over large areas.The main research contents of this paper are as follows:（1）Preparation of FA-based perovskite active layer based on two-step spin-coating method,to investigate the effect of high boiling point and strong complexing ability additive tetramethylene sulfoxide（THTO）in lead iodide precursor solution on the lead iodide morphology and device performance.It is found that the morphology of lead iodide thin films based on 5 vol%THTO has an ideal porous structure,which provides a wider specific surface area for the subsequent diffusion of organic amine salts.The highest efficiency of the corresponding device reaches22.82%,and the average efficiency of the devices is 22%.Compared with pure DMF as the lead iodide precursor solvent,the device performance is greatly improved.Then,the reasons for the difference in device performance are further analyzed:the SEM results show that the perovskite film obtained based on 5 vol%THTO has larger grain size,uniform distribution and dense no voids.（2）The light-absorbing layer is prepared based on a two-step blade coating method.Two solvent systems,DMF/DMSO and DMF/THTO are used to dissolve lead iodide powder to obtain a lead iodide precursor solution.The C-PbI₂film from DMF/DMSO is mainly composed of layered and dense small crystals,while the NC-PbI₂film from DMF/THTO is composed of flaky large-sized lead iodide grains and continuous and regular nano-ion channels.This is mainly due to the strong complexing ability between THTO and PbI₂,which induces the growth of lead iodide in the direction perpendicular to the substrate,resulting in continuous nanochannels in the film.SEM characterization shows that the perovskite film based on NC-PbI₂has larger grain size,better crystallinity,smaller roughness and better uniformity.The best device has a PCE of 22.77%,and retains more than 90%of the initial PCE after 1000hours of storage and more than 80%of the initial PCE after more than 800 hours in ambient air at 50°C.（3）5 cm×5 cm module were prepared,and the best efficiency is 18.65%.After more than 1000 hours storage,the modules still maintain more than 90%of the initial efficiency.Compared with the performance of smaller-area devices,the efficiency has a certain loss.The uniformity of the film is characterized by SEM,AFM and other tests.It can be found that the thickness difference of each area of variation through the whole film is small.The average R_qof the film is 39.8 nm,indicating that the large-area perovskite film prepared based on the two-step blade coating is relatively uniform.But it is also found there is a small amount of lead iodide residue at the end of the blade coating,which will affect the film quality.Even so,the two-step blade coating method shows great advantages for preparing large-area perovskite films.