Regulating Crystallization Process Of MaPbI₃ Perovskite Film By Solvent Engineering

In recent years,organic-inorganic hybrid perovskite solar cells(PSCs)have attracted extensive attention on account of the advantages of high power conversion efficiency(PCE),low-cost and simple process steps.The preparation of perovskite polycrystalline films with large grain size and low defect density is a prerequisite for the realization of high PCE and device stability.However,the perovskite films prepared by solution process always have many problems such as small crystal size and many defects,which limit the rapid development of high-efficiency perovskite.The current research work mainly focuses on the regulation of the nucleation and growth process of perovskite crystals by means of precursor doping,regulation of poor solvents and thin film post-treatment,which always involve the preparation of solution.To systematically explore the important role of solvent factors in the perovskite crystallization process,in this work,efforts are mainly concentrated on the critical steps of perovskite manufacturing processes,and indepth analysis of solvent impact on different stages of perovskite film formation.Then the internal relationship among solvent properties,perovskite polycrystalline morphology and photovoltaic performance was established.The main contents are as follows:(1)The ternary precursor solvent system of N,N-dimethylformamide(DMF),Nmethylpyrrolidone(NMP)and chlorobenzene(CB)was constructed to regulate the crystallization process of perovskite,and the PSCs with excellent performance were achieved using perovskite precursors with lower precursor solution concentration.The addition of CB accelerated the nucleation rate of perovskite and the evaporation rate of solvent,which promoted the rapid solidication of perovskite,and obtained thicker active layer films at low precursor concentration.Based on this precursor solution with ternary solvent system,the final performance of PSCs reached 17.37%.The perovskite precursor solution based on the ternary solvent system can obtain high device performance without affecting the quality of perovskite films,which provides an improved idea for the large scale industrialization of PSCs.(2)The passivation mechanism of organic passivator guanidine hydrochloride(GACl)on perovskite films in isopropanol(IPA),toluene(Tol)CB and ethyl acetate(EA)was studied systematically,and the relationship between passivating solvent environment and perovskite photovoltaic performance was estabished.Because IPA has dissolution effect on perovskite film,the perovskite grains passivated by CACl/IPA can realize secondary growth process,and the grain size increases obviously.The impedance spectrum test further shows that GACl/IPA can effectively passivate the intrinsic defects,suppressing the carrier recombination.While CACl/Tol,CACl/CB and CACl/EA can only passivate perovskite surface defects.The filling factor(FF)of PSCs treated by GACl /IPA is increased from 71.91% to 79.05%,and the PCE improves from 15.66% to 18.65%.(3)A novel method of solvent vapor annealing assisted by flexible polymer film was proposed and applied to the preparation of perovskite films and photovoltaic devices.A cross-linked polydimethylsiloxane(PDMS)was used as a matrix of solvent vapor.By controlling the soaking time of PDMS flexible film in specific solvent,the quantitative control of solvent vapor annealing of perovskite film was realized.The PCE of the device is increased from 16.98% to 19.01% after Tol treatment with PDMS.The preliminary research result provides a new method for the preparation of high quality perovskite films.