Amorphous self-assembled multilayers for perovskite solar cells with improved reverse bias stability

Robust hole-selective interfaces are critical for the stability of perovskite solar cells, yet this requirement is inadequately addressed by self-assembled monolayers (SAMs). Here we combine (4-(7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid (CbzNaph) and its hydroxyl functionalized analogue (CbzNaphOH), which features intramolecular hydrogen-bonding interactions between the spacer and anchoring groups, to modulate SAM molecular packing. Increased steric hindrance promotes the formation of an amorphous self-assembled multilayer (a-SAMUL) with homogeneous packing. This amorphous layer acts simultaneously as a uniform, strongly adhesive binding medium that tightly couples the perovskite and substrate—thereby suppressing the formation of mobile ions—and as an efficient hole-selective contact with favourable energy-level alignment. Devices incorporating a-SAMULs achieve a certified efficiency exceeding 26% and reduced ion-migration-driven degradation. The devices exhibit reverse breakdown voltages exceeding −17 V and maintain operational stability for over 3,000 h with negligible degradation. These findings underscore the effectiveness of a-SAMULs in enhancing the long-term reliability of perovskite photovoltaics. © The Author(s), under exclusive licence to Springer Nature Limited 2026.