Regulation Of PbBr₂ Precursor Films For Preparing CsPbBr₃ Layer In All-inorganic Perovskite Solar Cells

Organic-inorganic metal halide perovskites,such as CH3NH3PbI3,are widely used as the light-harvesting layer of high-efficiency perovskite solar cells(PSCs).However,organic cations inherently cause poor thermal and illumination stability of halide perovskites,limiting long-term stability of devices.Recently,complete substitution of organic cations with inorganic Cs+ is considered as an effective way to improve thermal stability.Among all inorganic CsPbX3(X=I,Br,Cl),CsPbBr3 not only has excellent thermal stability,but also shows good structure stability,illumination stability and humidity stability at ambient environment.Besides,all inorganic PSCs(FTO/TiO2/CsPbBr3/Carbon)with carbon electrodes as back electrodes can withstand high operating temperature and high humidity.Hence,all inorganic PSCs have become one of research hotspots in recent years.However,the power conversion efficiency(PCE)of carbon-based all-inorganic CsPbBr3 PSC remains to be improved.On the one side,the optical band gap of CsPbBr3 is about 2.3eV,and CsPbBr3 can only absorb visible light spectrum below 550nm.On the other side,due to the solubility limitation of Br-in organic solvents,the preparation methods for CsPbBr3 films are limited.It is hard to fabricate high-quality CsPbBr3 light-harvesting layer.Therefore,this paper focuses on the preparation of CsPbBr3 thin film Firstly,mostly used two-step solution method based on crystallized PbBr2 precursor film for CsPbBr3 film was studied and discussed.Then,an improvement strategy with a wet PbBr2 precursor film was proposed to realize a rapid formation of CsPbBr3 film with improved quality.It provides valuable references for further understanding and optimizing the preparation of CsPbBr3 film.The main results are as follows:For conventional two-step solution method,main problems are the inconvenient conversion process and the rapid decomposition phenomenon.And inconvenient conversion causes the generation of a byproduct CsPb2Br5.For the improved strategy with a wet PbBr2 precursor film,the conversion process was accelerated.The decomposition phenomenon was weakened by the shortened reaction time.And the phase purity,crystallinity and surface coverage of CsPbBr3 films were improved.Based on improved CsPbBr3 films,all inorganic PSCs with carbon electrodes showed an optimized PCE of 5.25%,which was boosted by about 100%.To explain such improvement,the wet state of the PbBr2 precursor film is considered to benefit the diffusion of CsBr solution.And the direct substitution of DMF ligands and CsBr may reduce the energy barrier for the formation of CsPbBr3.The DMF is the organic solvent used to dissolve PbBr2.