Research On The Construction Of Efficient And Stable Perovskite Solar Cells By Doping Technology

Organic-inorganic metal halide perovskite solar cells(PSCs)have been proved as a promising photovoltaic technology,due to their high efficiency,easy-fabrication,and low-cost.Although the laboratory certified efficiency of perovskite solar cells has exceeded 25%,there is still a certain gap compared with its theoretical limit(Shockley-Queisser limit).The loss of efficiency is mainly related to the defects in PSCs,which increases the proportion of nonradiation combination,and most of these defects are concentrated on the grain boundary of perovskite films and the interface between each functional layer.In addition,the instability of PSCs greatly prevents its large-scale commercialization.This paper improves the photovoltaic performance and stability of PSCs by doping NaCl,additive strategy,and solvent engineering.The main research contents of this paper are as follows:(1)The sodium chloride dopant is incorporated into the compact TiO2 electron transport layer at a low temperature by chemical bath deposition.It is demonstrated that the appropriate sodiumchloride additive can effectively passivate the bulk and surface defects of the intrinsic TiO2,including the oxygenvacancies-induced nonradiative recombination centers,improve electron extraction and collection,remarkably enhance the TiO2 conductivity,and further indirectly optimizes the morphology of perovskite layers.An efficiency up to 19.84%with small hysteresis is achieved by the PSCs based on 5.0 mol%sodiumchloride-incorporated TiO2 which exhibited the lower carrier recombination and faster charge transport.The device still maintains about 80%of its initial efficiency,after storaged under relative humidity of 40%in air for 800 h.(2)A novel small organic molecule N,1-diiodoformami-dine(DIFA)with the hydrophobic C-I group was synthesized and introduced into the FA0.85MA0.15PbI3(FA=HC(NH2)2)perovskite precursor solution.The morphology of perovskite films is improved and the grain size is increased significantly(up to 3 ?m),which make the grain boundary and trap densities of the films decrease significantly,thus diminishes the hysteresis of PSCs.The results show that the optimized devices with 2%DIFA additive show the best performance,as compared to the control devices,the power conversion efficiency(PCE)are improved from 19.07%to 21.22%,and the light,thermal,and environmental stability are remarkably enhanced.(3)We also introduced the volatile solid molecule glycolic acid(HOCH2COOH,GA)and the less-volatile variation of this compound,thioglycolic acid(HSCH2COOH,TGA)into a FA0.85MA0.15PbI3 perovskite precursor solution to investigate the effect on crystallization kinetics of perovskite films.The results indicate that the strong interaction between GA or TGA and Pb2+slows down the perovskite crystal growth process and facilitates the generation of large grained perovskite films.The films modified by the volatile GA molecule different from the common additive approach shows a superior crystallinity and a reduced defect density while pinholes appear when the less-volatile TGA is used.This is mainly due to the fact that GA volatilizes completely in the annealing process,which only affects the crystallization process of the perovskite films.However,after annealing,TGA with high boiling point always exists inthefilms,and there is still strong interaction between TGA and Pb2+.Consequently,a PCE as high as 21.32%is achieved for GA based solar cells,which is more than 13%higher than that of a pristine control device(PCE=18.85%).The use of TGA produces a continuous PCE decline with the best value of 17.79%.In addition,GA modified PSCs exhibit the best light,thermal,and humidity stabilities,due to the improved film formation.