Research On The Effect Of Mixed Lead Halide Sources On The Properties Of Perovskite Thin Films And Solar Cells Prepared By Vapor-Assisted Solution Processed Method

Nowadays,energy and environmental issues have become increasingly prominent,The development of renewable clean energy has become the key to alleviating energy and environmental problems.As an important member of renewable energy,the development of solar photovoltaic power generation has received people’s attention and support,which is also one of the most promising power generation.As a key technology in photovoltaic power generation,solar cells have become the focus of people’s research.Recently,perovskite solar cell has caused great concern in academia.Thanks to the better light absorption,appropriate forbidden band width and charge diffusion length,the efficiency of perovskite solar cells has increased from the initial 3.8% to 22% or more.Obtaining high-quality organic-inorganic halide perovskite films that have smooth and continuous surfaces and large crystal domains and possess photoelectrical properties preferable is of paramount importance to achieve high performance perovskite solar cells.The introduction of other halide ions into the synthesis process of methylammonium lead triiodide,CH₃NH₃PbI₃,to fabricate CH₃NH₃PbI₃-xXx（X = Cl or Br）（x ≈ 0）has been confirmed as an effective approach to optimize optoelectronic properties.Lead halide mixing method can optimize the perovskite thin film formation process,improve the film morphology,coverage,and promote electron transport at the film interface,reducing the electron recombination,thereby enhancing the conversion efficiency of perovskite solar cells.Here,we report on bromide regulated CH₃NH₃PbI₃ film formation through a low-pressure vapor-assisted deposition process.PbBr2 or PbCl2 was used to either replace or to be mixed with PbI2 to form pre-deposited films that were then reacted with CH₃NH₃ I vapor.Detailed structural,spectroscopic,and morphological characterizations of the perovskite films are applied to study the effect of halide ion in perovskite thin films.Results indicate that bromine incorporation slows down the perovskite formation process through formation of an intermediate phase,CH₃NH₃ PbBrxIy,which also improves the grain domains in the as-fabricated perovskite films.When mixed PbI2/PbBr2 films with a molar ratio of 1:4 were used as re-deposited films,an optimized PCE of 17.40% was obtained,with a short circuit current of 22.92 mA/cm2,an open circuit voltage of 1017 mV,and a fill factor of 77.50%.Meanwhile,The introduction of chlorine did not change the morphology of the perovskite thin films,and the efficiency of the cells decreased with the increase of chlorine content in the lead halide source.