A sustainable thermal regulation strategy using carboranes improves the stability and efficiency of all-perovskite tandem solar cells. Mixed Sn-Pb perovskites, promising photovoltaic materials, face challenges in stability due to poor thermal conductivity, leading to heat accumulation and degradation. Incorporating ortho-carborane (o-CB) into perovskites enhances thermal conductivity and heat transfer, reducing surface temperature by ~5°C under illumination. o-CB also facilitates hole extraction and reduces charge recombination, improving thermal stability. Mixed Sn-Pb cells retained 80% of their initial efficiency after 1080 hours at 85°C. When integrated into monolithic all-perovskite tandems, the cells achieved efficiencies over 27%. The tandem cell maintained 87% of its initial PCE after 704 hours of continuous operation. o-CB treatment improved film quality, reduced Sn oxidation, and enhanced interfacial contact, contributing to better thermal stability. The study also showed that o-CB treatment reduced interface recombination and improved charge transport, leading to higher PCEs. The results demonstrate that o-CB enhances both the efficiency and stability of perovskite solar cells, making them more suitable for commercial applications.A sustainable thermal regulation strategy using carboranes improves the stability and efficiency of all-perovskite tandem solar cells. Mixed Sn-Pb perovskites, promising photovoltaic materials, face challenges in stability due to poor thermal conductivity, leading to heat accumulation and degradation. Incorporating ortho-carborane (o-CB) into perovskites enhances thermal conductivity and heat transfer, reducing surface temperature by ~5°C under illumination. o-CB also facilitates hole extraction and reduces charge recombination, improving thermal stability. Mixed Sn-Pb cells retained 80% of their initial efficiency after 1080 hours at 85°C. When integrated into monolithic all-perovskite tandems, the cells achieved efficiencies over 27%. The tandem cell maintained 87% of its initial PCE after 704 hours of continuous operation. o-CB treatment improved film quality, reduced Sn oxidation, and enhanced interfacial contact, contributing to better thermal stability. The study also showed that o-CB treatment reduced interface recombination and improved charge transport, leading to higher PCEs. The results demonstrate that o-CB enhances both the efficiency and stability of perovskite solar cells, making them more suitable for commercial applications.