Preparation And Performance Optimization Of Cesium-Based All-Inorganic Perovskite Solar Cells

Energy shortage and environmental pollution have become the main obstacles to the realization of sustainable development in the world.So far,solar photovoltaic technology is the fastest developing new energy field is also the most effective technical means to solve these two problems.Halide perovskite is one of the most promising solar cell materials because of its excellent photoelectric properties such as low binding energy,long carrier life and low defect density.The general formula of perovskite material is ABX₃,in which various cations occupying the A and B sites of perovskite and anions in X halides make the photoelectric properties of the material tunable and define A complex material system.After about 10 years of development,the certified photoelectric conversion efficiency(PCE)of organic-inorganic hybrid perovskite solar cells reached 25.5%,close to that of silicon solar cells(26.7%).Nevertheless,organic-inorganic hybrid perovskite solar cells still face significant stability challenges.Due to the hygroscopicity and volatilization of organic cations,organic-inorganic hybrid perovskites will appear chemical instability when exposed to oxygen,water,light,especially high temperature.It is well known that inorganic materials are generally more stable than organic materials at high temperatures.The results show that the inorganic monovalent cation Cs⁺can meet the requirements of ABX₃ structure,and can replace MA⁺and FA⁺as A cation,forming A high humidity and heat stable CsBX₃(>350°C).At the same time,CsBX₃ is also the best choice for preparing series solar cells due to its suitable broadband gap.The development of all-inorganic CsPbX₃ solar cells has been extremely rapid,especially in the past two years,its photoelectric conversion efficiency has been improved from 10%initially to 19%.The most common CsPbX₃ includes CsPbI₃,CsPbI₂Br,Cs PbIBr₂,and Cs PbBr₃,based on the X-site different halogen anions.As a representative of inorganic perovskite solar cells,CsPbI₃ has an appropriate band gap of 1.73 e V.Although CsPbI₃ solar cells have achieved a photoelectric conversion efficiency of up to 19%,poor phase transition from black cubic phase to yellow non-perovskite phase occurs at room temperature,indicating material instability.Compared with I-rich CsPbI₃ and CsPbI₂Br,Br-rich CsPbBr₃ and CsPbIBr₂ show better long-term phase stability in indoor environments.Despite the rapid development of all-inorganic perovskite solar cells,more and more research work has been reported,but there are still many thorny problems to be solved.For example,the poor solubility of Cs precursor solution greatly limits the thickness of inorganic perovskite film,hinders the realization of good morphology,and leads to poor light absorption capacity and current density.Moreover,I-rich perovskite is prone to phase transformation due to its high humidity sensitivity,which is not conducive to the stability of photovoltaic devices.In order to control the growth of inorganic perovskite films or ensure the formation of perfect crystals,methods such as solvent engineering,interface engineering and defect passivation have been successfully used to prepare inorganic perovskite films,which can effectively slow down the crystallization rate and contribute to the accurate control of crystal growth.In addition,the inorganic perovskite in the introduction of additional organic components or inorganic ions can participate in the crystallization process of perovskite,thus improve the moisture,heat and phase stability of the film,which can inhibit the compound and high carrier mobility of good inorganic membrane structure,so as to realize the all-inorganic perovskite high performance of solar cells.In order to realize the performance advantages of all-inorganic perovskite solar cells and achieve full coverage and high crystallinity of perovskite films,the work of this paper includes the following three aspects:(1)CsPbIBr₂ thin films were prepared on mesoporous titanium dioxide(m-TiO₂)substrate by one-step rotary coating method.PbI₂-ethanolamine-dimethyl Sulfoxide(PED)mixed solution was used as an interface modifier to modify the m-TiO₂/CsPbIBr₂ thin film interface,and promote the further diffusion of CsPbIBr₂ precursor solution into m-TiO₂ thin film.The use of PED makes CsPbIBr₂ fill the pores in m-TiO₂,improves the interface relationship between m-TiO₂ and CsPbIBr₂,successfully inhibits the interface recombination and improves the electron transfer capacity,thus improving the conversion efficiency of CsPbIBr₂ solar cells.(2)InBr₃ was introduced into DMF precursor solution of PbBr₂,and Cs PbBr₃film was prepared on m-TiO₂ substrate by multi-step solution spin coating method.The introduction of InBr₃ can make PbBr₂ crystals grow in order along multiple orientations,and make PbBr₂ films evolve from coarse and uneven grain distribution into large and uniform porous films with pores.This morphological change promotes the full diffusion and homogeneous reaction of Cs Br in PbBr₂ film,and is conducive to the formation of InBr₃:Cs PbBr₃ film with good density.After optimization,the efficiency of InBr₃:Cs PbBr₃ solar cell is 6.48%,especially the open circuit voltage of the device has been significantly improved.(3)Combined with relevant experimental results in(2),high quality films with good density were prepared on SnO₂ by introducing InBr₃ into PbBr₂ precursor solution and adjusting the concentration of PbBr₂.While the light absorption capacity of CsPbBr₃ film is effectively improved,the defect density and the recombination rate of carriers in the perovskite film are also effectively inhibited.When InBr₃ in the precursor solution is 0.21M and PbBr₂ concentration is 1.3 M,the prepared CsPbBr₃ solar cell with planar structure and no hole transport layer shows the optimal conversion efficiency of 6.58%.JSC=6.72 m A/cm²,VOC=1.38 V and FF=0.71.