Preparation Of All-Inorganic Perovskite Polycrystalline Films And Quantum Dots For Application In Solar Cell

Solar energy is inexhaustible which can alleviate the problem of energy shortage in human society.Solar cell is capable of directly converting solar energy into electrical energy to serve human society.The development of high-performance solar cells is beneficial for the more efficient use of solar energy in human society.Perovskite solar cell has received widespread attention due to their low raw material cost and simple preparation process.In a short period of more than ten years,it has achieved an optimal power conversion efficiency of 25.5%with an astonishing development speed.In comparison with organic-inorganic hybrid perovskite solar cells,all-inorganic perovskite solar cells have obvious advantages in high temperature stability and can further promote the development of photovoltaic field by forming tandem solar cells with silicon solar cells.However,CsPbI3 perovskite polycrystalline solar cell,which can achieve the highest power conversion efficiency in all-inorganic perovskite solar cells until now,is unstable at room temperature,because cubic CsPbI3 perovskite tends to be converted into orthorhombic CsPbI3 perovskite,which is unsuitable as a photoactive layer.Adding Br-to part of the halogen sites of CsPbI3 perovskite to form CsPbI2Br perovskite is beneficial to improve its stability at room temperature.For CsPbI2Br perovskite polycrystalline solar cell,the improvement of photoactive layer and interfaces can further promote the development of its device performance.In this paper,methyl acetate was applied as anti-solvent to improve the processes of nucleation and crystal growth of CsPbI2Br perovskite polycrystalline film,with the purpose of achieving high-quality photoactive layer.The method is beneficial for improving the interface contact between photoactive layer and hole transport layer.In addition,TiO2 nanocrystals were prepared by a simple method to passivate SnO2 electronic transport layer,with the purpose of promoting the transfer of charge carriers from photoactive layer to electronic transport layer.Eventually,through the strategy of double interface engineering,the device performance of CsPbI2Br perovskite polycrystalline solar cell was obviously enhanced with an optimal power conversion efficiency of 15.86%.Apart from the method of adding Br-to the halogen sites of CsPbI3 perovskite to form CsPbI2Br perovskite,the realization of CsPbI3 perovskite quantum dot can also improve the stability of cubic CsPbI3 perovskite at room temperature.For CsPbI3 perovskite quantum dots solar cell,insulated long chain ligands at the surfaces of CsPbI3 perovskite quantum dots have an adverse effect on the transport of charge carriers in the photoactive layer.In this paper,dipropylamine was added into methyl acetate to post-treat CsPbI3 perovskite quantum dot film with the purpose of more effectively eliminating the insulated long chain ligands.Acylation reaction can take place between dipropylamine and oleic acid ligands,thus enabling the dynamic equilibrium of ligands at the surfaces of CsPbI3 perovskite quantum dots to be broken,and then promoting the elimination of long chain ligands from the surfaces of CsPbI3 perovskite quantum dots.Through this process,the coupling of CsPbI3 perovskite quantum dots in photoactive layer was enhanced to improve the mobility of charge carriers,thus increasing the power conversion efficiency of CsPbI3 perovskite quantum dot solar cell to 14.9%,which is mainly attributed to the increase of short-circuit current density.In addition,although the production of CsPbI3 perovskite quantum dots can be obviously increased when taking only one step to wash and purity,enough thickness of the photoactive layer can not be obtained by the method of layer-by-layer deposition using pure methyl acetate post-treatment.After adding dipropylamine into methyl acetate,a photoactive layer with enough thickness can be obtained,thus a high-performance CsPbI3 perovskite quantum dot solar cell was prepared with a balance between yield and performance.Although the elimination of long chain ligands at the surfaces of CsPbI3 perovskite quantum dots is beneficial for the carrier mobility in quantum dots photoactive layer,the process easily introduce trap states,thus limiting further development of CsPbI3 perovskite quantum dots solar cell.In this paper,Triphenyl phosphite was added into methyl acetate to post-treat CsPbI3 perovskite quantum dots film,by bonding with the quantum dots surfaces.The existence of triphenyl phosphite does not affect the coupling of CsPbI3 perovskite quantum dots in photoactive layer,but it can passivate the trap states formed in the process of ligand removal.As a result,the method can not only maintain a high short-circuit current density,but also achieve a high fill factor approaching 80%,thus pushing the optimal power conversion efficiency beyond 15%.Finally,to solve the problem of lead in CsPbI3 perovskite quantum dots which can result in serious environmental pollution,CsSnI3 perovskite quantum dots have been synthesized by the method of thermal injection under 120℃.The shape of as-prepared CsSnI3 perovskite quantum dots is hexagonal which is obviously different from the shape of cube in previous reports,but the crystal phase is the same orthogonal crystal phase.In addition,the asprepared CsSnI3 perovskite quantum dots can maintain stable for 60 days under nitrogen atmosphere,which is better than the previous reports.Hence,the method in this thesis can promote the application of CsSnI3 perovskite quantum dots in the field of high-performance photovoltaics.