Study On Performance Improvement Of Perovskite Solar Cells Based On Doping And Interface Modification With Cesium Salt

Perovskite solar cells have made impressive strides with maximum power conversion efficiency from 3.8%initially to 25.5%by now.However,there is still a certain gap between the theoretical limit efficiency.The energy level matching between the electron transport layer and the perovskite layer,charge transfer and the defect states at the interface are the key factors affecting the efficiency of perovskite solar cells.SnO₂is considered as one of the most effective electron transport layer materials due to its excellent properties such as high electron mobility,strong chemical stability and easy preparation at low temperature.However,some defects and non-radiative composite centers will inevitably be generated during the fabrication process.,resulting in energy loss and performance reduction of the device.In addition,defects such as oxygen vacancies and poor contact at the interface can lead to ion migration and charge accumulation of perovskite components,resulting in serious hysteresis of current and voltage characteristics.The optimization of SnO₂ electron transport layer is helpful to improve the device performance and promote the development of perovskite solar cells.In this paper,cesium salt is selected as the optimized material.The large cation Cs⁺can well match the lattice of perovskite,relieve the lattice strain,and fill the defects of organic cation vacancies without damaging the lattice structure of perovskite.While the large anion TFSI^-can coordinate uncoordinated Sn⁺ions and neutralize oxygen ion vacancies to reduce non-radiative recombination losses.In this paper,different concentrations of cesium salts are used to doping SnO₂ electron transport layer,and the corresponding characterization and analysis of the photoelectric performance of SnO₂electron transport layer,perovskite layer and devices are carried out.Through this study,it is found that appropriate concentration of cesium salt doping can improve the conductivity of SnO₂ electron transport layer,promote the extraction and transport of electrons,inhibit the hysteresis caused by charge accumulation at the interface,effectively improve the photoelectric performance of perovskite solar cells.However,it has no obvious effect on crystal size and crystal quality of perovskite layer.On the basis,we use cesium salt as interface modified layer,directly effects on the interface between SnO₂ electronic transport layer and perovskite.It can effectively passivate the defect states at the interface,enhance the energy level alignment,promote the extraction and transport of charge and improve the crystallization quality of perovskite.After interface modification with cesium salt,the photoelectric conversion efficiency of perovskite solar cells is greatly increased from 19.93%to 22.05%,and the hysteresis of devices is significantly reduced.