Conventional hole transport layer (HTL) Spiro-OMeTAD requires the addition of hygroscopic dopants due to its low conductivity and hole mobility, resulting in a high preparation cost and poor device stability. Cuprous thiocyanate (CuSCN) is a cost-effective alternative with a suitable energy structure and high hole mobility. However, CuSCN-based perovskite solar cells (PSCs) are affected by environmental factors, and the solvents of an HTL can potentially corrode the perovskite layer. In this study, a Co 3 O 4 /CuSCN/Co 3 O 4 sandwich structure was proposed as an HTL for inorganic Cs 2 PbI 2 Cl 2 /CsPbI 2.5 Br 0.5 PSCs to address these issues. The Co 3 O 4 layers can serve as buffer and encapsulation layers, protecting the perovskite layer from solvent-induced corrosion and enhancing hole mobility at the interface. Based on this sandwich structure, the photovoltaic performances of the Cs 2 PbI 2 Cl 2 /CsPbI 2.5 Br 0.5 PSCs are significantly improved, with the power conversion efficiency (PCE) increasing from 9.87% (without Co 3 O 4 ) to 11.06%. Furthermore, the thermal stability of the devices is also significantly enhanced, retaining 80% of its initial PCE after 40 h of continuous aging at 60 °C. These results indicate that the Co 3 O 4 /CuSCN/Co 3 O 4 sandwich structure can effectively mitigate the corrosion of the perovskite layer by solvents of an HTL and significantly improves the photovoltaic performance and thermal stability of devices.