Universal in-situ crosslinking strategy improves stability of inverted perovskite solar cells

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

The study, published in the journal Nature, was published by Professor Chunlei Yang and a team led by him. Professor Zhang Jie and Professor Alex K.-Y from the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences. Zheng from City University of Hong Kong developed a universal in-situ cross-linking structural reinforcement strategy for SAM molecules to effectively address the operational stability issue caused by buried interface degradation in high-efficiency inverted perovskite solar cells.

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

The azide group of JJ24 is thermally activated and forms covalent cross-links with the alkyl chains of CbzNaph molecules in situ, forming a tightly assembled co-SAM layer.

This structure enhances the preferred orientation of CbzNaph and suppresses the exposure of the TCO substrate surface caused by molecular shaking under light and thermal stress. Therefore, the degradation at the perovskite-embedded interface is suppressed and the non-radiative recombination losses at the device interface are significantly reduced.

Using this strategy, the researchers fabricated an inverted perovskite solar cell that achieved a certified power conversion efficiency (PCE) of 26.9%. The device exhibited top-level stability with zero efficiency loss after 1,000 hours of continuous operation based on ISOS-L-2 test standards and maintained more than 98% of the initial PCE after 700 thermal cycles between -40 °C and 85 °C.

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