Mixed Sn-Pb perovskites are attracting significant attention due to their narrow bandgap and consequent potential for all-perovskite tandem solar cells. However, the conventional hole transport materials can lead to band misalignment or induce degradation at the buried interface of perovskite. Here we designed a self-assembled material 4-(9H-carbozol-9-yl)phenylboronic acid (4PBA) for the surface modification of the substrate as the hole-selective contact. It incorporates an electron-rich carbazole group and conjugated phenyl group, which contribute to a substantial interfacial dipole moment and tune the substrate's energy levels for better alignment with the Sn-Pb perovskite energy levels, thereby promoting hole extraction. Meanwhile, enhanced perovskite crystallization and improved contact at bottom of the perovskite minimized defects within perovskite bulk and at the buried interface, suppressing nonradiative recombination. Consequently, Sn-Pb perovskite solar cells using 4PBA achieved efficiencies of up to 23.45%. Remarkably, the 4PBA layer provided superior interfacial chemical stability, and effectively mitigated device degradation. Unencapsulated devices retained 93.5% of their initial efficiency after 2000 h of shelf storage. (c) 2024 Science China Press. Published by Elsevier B.V. and Science China Press. All rights are reserved, including those for text and data mining, AI training, and similar technologies.