Interconnection layers for tandem perovskite solar cells: research advances and optimization strategies

The interconnection layers (ICLs) are critical components in perovskite tandem solar cells that directly determine the power conversion efficiency and operational stability of the devices. While ICLs have attracted widespread attention and numerous studies have reported their experimental performance, a systematic theoretical framework and an in-depth understanding of their holistic working mechanisms are still lacking. This review systematically elaborates the material systems, core functions, and evaluation criteria of ICLs in perovskite tandem solar cells, and presents an in-depth analysis of ICL-induced optoelectronic signal losses, intrinsic defects, and multi-field coupling failure mechanisms. In view of the intrinsic limitations of mainstream materials such as ITO, self-assembled monolayers and ultrathin metal layers, as well as the underdeveloped triple-junction interconnection systems, this work summarizes and systematically distills integrated optimization strategies spanning material modification, interfacial engineering, and custom-designed architectures based on state-of-the-art research progress. Furthermore, forward-looking perspectives are proposed regarding indium-free materials, intelligent molecular design, and low-temperature large-area fabrication techniques. This study aims to build a systematic theoretical framework for ICL research and provide theoretical support for the development of high-performance and scalable perovskite tandem solar cells.