Doping Modification And Energy Level Tuning Of Highly Efficient And Stable Inorganic CsPbI₂Br Perovskite Solar Cells

Metal halide perovskite solar cells(PSCs)have attracted much attention due to their high photoelectric conversion efficiency and low cost.However,the high-efficiency organic-inorganic hybrid PSCs that contain volatile organic components are unstable under operation for a long time,which postpones the commercial application process for PSCs.Recently,inorganic Cs-based perovskite materials have been widely studied due to their excellent photothermal stability.CsPbI2Br is one of the inorganic perovskite materials,which possesses high phase stability and a suitable optical band gap(1.91 eV).It has great potential to be applied in tandem solar cells.Nevertheless,the photoelectric conversion efficiency of CsPbI2Br PSCs is still far lower than that of the organic-inorganic hybrid PSCs,and the electron and hole transport layers used in PSCs are expensive and unstable under ultraviolet light.In this thesis,the methods of modification and energy level tunning are applied to improve the quality of perovskite films,promote charge transfer,and simplify the device structure.The inorganic CsPbI2Br PSCs with low-cost,high-efficiency and high-stable are successfully prepared.The main research contents are as follows:(1)A small amount of CaCl2 additive was introduced into the CsPbI2Br perovskite precursor solution to improve the crystalline quality of the perovskite film and construct energy level matching.The crystallization rate of CsPbI2Br films is delayed to obtain high-quality perovskite films by doping CaCl2.In addition,the Fermi level of the CsPbI2Br is changed by the added CaCl2 to show heavy n-type doping.The separation and transport of carriers are promoted with the increased built-in electric field.As a result,the optimized CsPbI2Br PSCs show a highest open circuit voltage(Voc)of 1.32 V and a record efficiency of 16.79%.Meanwhile,high air stability is demonstrated for a CsPbI2Br PSCs with 90%of the initial efficiency remaining after more than 1000 h aging in air.High-performance CsPbI2Br PSCs doped with CaCl2 are expected to be used in tandem solar cells.(2)The low-cost and high-stability CsPbI2Br PSCs could be prepared through adjusting energy level.The work function of FTO is improved by hydrothermal treatment of thioacetamide.The energy gap between FTO and CsPbI2Br perovskite is reduced,which promotes the transmission of electrons from perovskite to FTO.In addition,the quality of the perovskite film prepared by thioacetamide was significantly improved.As a result,the Voc of electron transport layer-free CsPbI2Br PSCs reached 1.30 V,and an efficiency of 15.10%was obtained.The efficiency of charge transport layer-free(CTL-free)CsPbI2Br PSCs based Pt electrode finally reached 11.03%.Meanwhile,high air stability is demonstrated for unencapsulated CTL-free CsPbI2Br PSCs with 98%of the original efficiency remaining after more than 40 days aging in 25%relative humidity air.The preparation of CTL-free CsPbI2Br PSCs with low-cost and high-stability provides a new route for the commercial application of PSCs.