Caesium based inorganic halide perovskite are promising alternatives to address the degradation issue of the organic-inorganic hybrid halide perovskites. However, high iodine content in these inorganic perovskites leads to structural instability upon exposure to moisture. In this work, the stoichiometry of CsPbI2Br perovskite is slightly tuned and its effect on structural stability and device performance is studied. Afterward, the charge transport layers are optimized to improve the charge extraction in perovskite solar cells. Finally, the device performance is further improved via interfacial modification. The optimized device yielded a power conversion efficiency (PCE) of 9.7%.