A major challenge in PSCs lies in the carrier transport losses induced by band misalignment and elevated series resistance, which adversely impact the fill factor and device stability, ultimately restricting the overall power conversion efficiency. Due to their tunable band gaps, low fabrication cost, strong light-harvesting capability, adequate carrier lifetime, chemical stability, and environmentally benign nature, chalcogenide perovskites have emerged as highly promising materials for optoelectronic applications. In this study, the quaternary semiconductor nanostructure Cu2MnSnS4 (CMTS) was synthesized via a simple and cost-effective hot-injection method and investigated as an alternative inorganic hole transport layer (HTL) candidate. Indium tin oxide-based perovskite solar cells without any metal oxide interlayer achieved a remarkable PCE of 9.87% and retained more than 92% of their initial efficiency after 720 hours, demonstrating enhanced stability. These findings highlight the critical role of cation–anion interactions in improving device stability and underscore the importance of developing innovative, low-cost, and efficient inorganic HTL materials for the commercial advancement of perovskite solar cells.