Effects Of Additives And Compositional Regulation On Defects And Stability Of Tin-Lead Mixed Perovskites

During the last ten years,perovskite solar cells(PSCs)have been a hot topic in the field of photovoltaic.As early as the 1970s,for the first time,metal halide perovskites have been synthesized and reported.The typical structure of perovskite is ABX3.A site mainly consists of Cs,CH3NH3(MA)and NH2CHNH2(FA),B site mainly consists of metal ions such as lead and tin,X site is mainly composed by halogen I,Cl and Br.In 2009,Miyasaka published the first article which applied MAPbI3 into dye-sensitized cells and finally achieved the efficiency of 3.8%.By 2021,through the unremitting efforts of worldwide researchers,the efficiency of single junction perovskite solar cells has surprisingly reached 25.5%.Its rapid development can be compared with the most widely used silicon cells in the market.However,the element of lead in perovskite is highly toxic and is considered as a huge obstacle for the future commercialization and industrialization of perovskite solar cells.Therefore,low-lead perovskite has attracted widespread attention.Among the low-lead perovskite,tin-lead mixed perovskites stand out from many low-lead perovskite materials because of their low toxicity,narrow band gap and high charge mobility.In this thesis,the performance and stability of tin-lead perovskite solar cells are optimized by additive engineering and compositional regulation.Although organic-inorganic tin-lead mixed perovskites is considered as one of the most promising low-bandgap photovoltaic materials to replace lead-based perovskites,however,due to the poor chemical stability of tin compared to lead,there are many challenges remain in the morphology,crystallinity and stability of tin-lead mixed perovskite films.Firstly,in order to reduce the ion defects and the film quality problems in the perovskite film,a small amount of potassium thiocyanate(KSCN)was introduced into the perovskite precursor solution using additive engineering and therefore high quality tin-lead mixed perovskite films were successfully obtained.It has been shown that potassium ions can enter the interstitial position between perovskite crystal structures and interact with iodine ions in perovskite to reduce the formation of iodine defects.In addition,thiocyanate ions can be combined with metal ions in perovskite precursor solution,which greatly slows down the film formation and crystallization process of perovskite,thus making the perovskite grain increase and grain boundary decrease.The film quality is greatly improved.Furthermore,a high efficiency of 15.14%were obtained by further optimization of potassium thiocyanate concentration in MA0.5FA0.5Pb0.5Sn0.5I3 PSCs.Secondly,in order to solve the problem of low open circuit voltage and poor stability of tin-lead mixed perovskite solar cells,this paper introduces two-dimensional material phenylethanamine bromide(PEABr)into tin-lead mixed perovskite solar cells by using the method of compositional regulation.The stability of tin-lead mixed perovskite solar cells has been greatly improved because of the advantages of hydrophobic nature and oxygen prevention of PEA+.Moreover,because PEA and Br ions can regulate the bandgap of perovskite layer,the carrier transport defects between the perovskite layer and the carrier transport layer in the solar cell devices can be effectively reduced,and the carrier transport is effectively enhanced.As a result,the efficiency of tin-lead hybrid perovskite solar cells after PEABr optimization was improved to 16.6%and the device stability is significantly enhanced.Finally,the photoelectric properties and stability of tin-lead mixed perovskite are optimized by additive engineering and compositional regulation,which contributes to the further development of perovskite solar cells and national photovoltaic industry.