Hole-selective self-assembled monolayers (SAMs) are ultrathin organic films that play a crucial role in modern optoelectronic devices, particularly in perovskite and silicon-perovskite tandem solar cells. However, their inherent instability often compromises operational performance of the device.

In a study published in Nature, a team led by Prof. YANG Chunlei and Assoc. Prof. ZHANG Jie from the Shenzhen Institute of Advanced Technology of the Chinese Academy of Sciences, and Prof. Alex K.-Y. Jen from City University of Hong Kong, developed a universal in-situ cross-linking conformational reinforcement strategy for SAM molecules, effectively addressing operational stability issues caused by buried interface degradation in high-efficiency inverted perovskite solar cells.

The researchers designed a novel azide-functionalized SAM molecule, JJ24, featuring an optimized carbon chain length. This molecule can enhance the distribution uniformity of the host SAM molecule CbzNaph on transparent conductive oxide (TCO) substrate, and can effectively suppress the formation of defects and voids during the self-assembly process. 

The azide group in JJ24 can be thermally activated to form in-situ covalent cross-linking with alkyl chains of CbzNaph molecules, creating a tightly assembled co-SAM layer. This structure improves the preferential orientation of CbzNaph and suppresses TCO substrate surface exposure caused by molecular swing under light and thermal stress. Thus, degradation at perovskite buried interface is inhibited, and non-radiative recombination losses at device interface are significantly reduced.

Using this strategy, the researchers fabricated inverted perovskite solar cells which achieved a certified power conversion efficiency (PCE) of 26.9%. The devices exhibited zero efficiency degradation after 1,000 hours of continuous operation under ISOS-L-2 testing standards and retained over 98% of their initial PCE after 700 thermal cycles between –40°C and 85°C, showing top-tier stability.

This study provides a practical strategy to enhance the operational stability of high-efficiency SAM-based devices on rough substrates, with significant implications to advance the commercialization of inverted perovskite photovoltaics and next-generation perovskite-based tandem solar cells.