Inorganic perovskites have good stability and superior optoelectronic properties, making them to be excellent absorbers for solar cells. However, the high interface defect density limits the improvement of efficiency and stability. In this paper, we conceived a new CsPbI2Br based perovskite solar cell (PSC) architecture featuring n-i-p configuration: FTO/SnO2/CsPbI2Br/CuI/Au. The interface key factors such as defect density and thickness of CsPbI2Br, SnO2 and CuI, interface defect density and band offset at SnO2/CsPbI2Br and CsPbI2Br/CuI interfaces were optimized via Solar Cell Capacitance Simulator (SCAPS), resulting in Power Conversion Efficiency (PCE) of 22.14% with open circuit voltage (VOC) of 1.50 V, short-circuit current density (JSC) of 16.86 and fulfill factor (FF) of 87.81%. Our study indicates that electronic transport layer has a greater impact on the performance of perovskite devices than hole transport layer. Furthermore, the decrease in VOC caused by interface defects has a significant impact on PCE, while valence band offset has a greater impact on PCE than conduction band offset. All the results turn out that reducing interface defects and adjusting the band offset of SnO2/CsPbI2Br interface can effectively improve the performance of perovskite solar cells.