Mixed Sn-Pb perovskites are promising photovoltaic materials, but their scalability and application require improved stability. Poor thermal conductivity leads to heat accumulation, accelerating degradation. This research introduces a thermal regulation strategy using carboranes, specifically *ortho*-carborane (*o*-CB), improving heat transfer. *o*-CB lowers surface temperature, facilitates hole extraction, and reduces recombination. Mixed Sn-Pb cells show enhanced thermal stability (80% efficiency after 1080 h at 85 °C). All-perovskite tandems achieve efficiencies over 27%, maintaining 87% initial PCE after 704 h of operation.
