Herein, solution-processible inorganic hole-transport layer (HTL) of a perovskite solar cell that consists of CuGaO2 nanoparticles and CuSCN, which leads to an improved device performance as well as long-term stability, is reported. Uniform films of CuGaO2 are prepared by first treating CuGaO2 nanoparticles with aminosilane that leads to well-dispersed CuGaO2 solution, followed by spin-coating of the suspension. Subsequent spin-coating of CuSCN solution onto the CuGaO2 forms a smooth HTL with excellent coverage and electrical conductivity. Comparing to the reference device with CuSCN HTL, the CuGaO2/CuSCN device improves carrier extraction and reduces trap density by ≈40%, as measured by photoluminescence and capacitance analysis. Excellent thermal stability is also demonstrated: ≈80% of the initial efficiency of the perovskite solar cells with the CuGaO2/CuSCN HTL is retained after 400 h under 85 °C/85% relative humidity environment.