Perovskite solar cells are emerging all-solid-state planar solar cells that have grown rapidly since they were first discovered in 2009. It has been reported that the power conversion efficiency of organic-inorganic hybrid perovskite solar cells has exceeded 26%. Compared with organic-inorganic hybrid perovskite solar cells, inorganic perovskite materials have become one of the hotspots in the field of perovskite solar cells due to their good thermal stability and chemical stability. Among them, CsPbI2Br-based perovskite solar cells have shown great potential to achieve high-efficiency perovskite solar cells. However, the commonly used deposition method induces defects in the perovskite material, resulting in loss of VOC, hysteresis effect, and poor stability. This thesis developed organic HTLs-involved CsPbI2Br perovskite solar cells. Following the optimisation of the deposition method, post-treatment, and additive engineering, defects in the CsPbI2Br materials were reduced and the performance of inverted CsPbI2Br-based perovskite solar cells was improved. In Chapter 5, the optimisation of inverted CsPbI2Br-based perovskite solar cells was completed by tuning the solvent composition and annealing process. In Chapter 6, an electron donor phenylmethylammonium iodide (PMAI) was inserted into inverted CsPbI2Br-based perovskite solar cells to reduce the defect density of CsPbI2Br. The performance of PMAI-treated devices improved from 11.35% of PCE to 12.67% of PCE with minimal hysteresis. In Chapter 7, a bifunctional additive NH4Ac was introduced in the CsPbI2Br precursor solution. The addition of NH4Ac not only modified the wettability between HTL and perovskite precursor but also facilitated the decrease of defects in the CsPbI2Br material. The champion PCE of 12.86% was achieved with negligible hysteresis.