Counter electrodes for perovskite solar cells: materials, interfaces and device stability

Perovskite solar cells (PSCs) show great promise for scalable application owing to the advantages of high conversion efficiency and solution processable fabrication. However, the material cost and device stability greatly hinder the development of PSC technology. Counter electrodes, as one of the indispensable components in PSCs, play critical roles in charge collection and device protection. However, the commonly used noble metals (Ag or Au) are unaffordable for the scalable application of PSCs, and the interfacial instability caused by metal corrosion has significantly threatened the reliability of PSCs. Here we provide a comprehensive review of the development of counter electrodes in the aspects of materials, interfaces and device stability. Firstly, the fundamental understanding of the roles and limitations of counter electrodes are summarized, including the basic requirements and influencing factors for counter electrodes. Moreover, different degradation mechanisms and various interfacial characterization methods have been discussed. Furthermore, recent development of alternative counter electrodes and their photovoltaic performance are reviewed. This review provides a comprehensive understanding of the fundamental material limitations and guides the design of robust and efficient counter electrodes for PSCs.