Experimental Study On Preparation Process Of Large Grained Organic-Inorganic Hybrid Perovskite Films And Optimization Of Device Performance

Organic-inorganic lead hybrid perovskites have emerged as ideal light-absorbing materials for high efficient solar cells due to their advantages in low cost,solution-processablility.Solar cells based on perovskite materials,so called perovskite solar cells（PSCs）show a shocking boost in power conversion efficiency（PCE）from3.8%in 2009 to 22.7%in 2018,making it the most commercially attractive solar cell technology at present.However,the grain size of the perovskite films prepared by common preparation method is very limited,approximately approach 200 nm,thus resulting in a huge number of grain boundaries per unit area.The most recent researches indicate that grain boundaries in perovskite film are likely to function as:1)centralized areas of electronic trap states and 2)pathways for ion migration.The electronic trap states not only serve as barriers for charge transport,but also enhance non-radiative recombination,severely reducing the charge carrier life time,and thus the overall photovoltaic device performance.Therefore,it is desirable to develop a method to prepare perovskite films with improved grain size.This paper mainly focus on the preparation of highly uniform and pinhole-free perovskite films with micron scale grains and reduced grain boundaries under ambient condition to fabricate high efficient PSCs.In this work,the major points are summarized as follows:1.A new intermittent annealing method（IA）for the preparation of pinhole-free highly uniform and well-crystallized perovskite films was developed.The morphology,structure,optical,and electrical properties of perovskite films treated by traditional annealing method and the new intermittent annealing method are compared.All of the films were prepared by one-step spin-coating method with ethyl acetate as an anti-solvent under ambient conditions.The films treated by the traditional annealing method tend to exhibit weak ultraviolet–visible absorption,While the intermittent annealing method is beneficial for preparing highly uniform perovskite films with larger grain size.The method is applicable to MAPbI₃ and Br-doped perovskite materials with different precursor concentration.The best device treated by the intermittent method under ambient condition showed an average PCE of 14.5%under simulated AM 1.5 irradiation,which is a quarter enhancement in comparison with that of 11.77%for the device treated by the traditional annealing method.In addition,the repetition test results suggest that the devices fabricated by the intermittent annealing method is highly reproducible.2.A new multi-stage solvent annealing method（MSA）for the preparation of pinhole-free highly uniform and well-crystallized perovskite films was developed.MAPbI₃ perovskite films with average grain size exceeded 2μm and largest grain size exceeded 4μm,which is the largest MAPbI₃ columnar grain size reported up to now,are prepared under ambient conditions.The morphology,structure,optical,and electrical properties of perovskite films treated by traditional annealing method and the multi-stage solvent annealing method are compared.As a result,PSCs based on the MSA method deliver a best PCE of up to 17.19%in 0.24 cm²,which is a huge enhancement in comparison with that of 11.94%for the devices treated by the traditional annealing method.The repetition test results suggest that the devices fabricated by the multi-stage slovent method is highly reproducible,too.