Recent Progress of Solution‐Processed Thickness‐Insensitive Cathode Interlayers for High‐Performance Organic Solar Cells

Abstract Organic solar cells (OSCs) have shown great applications potential in flexible/wearable electronics, indoor photovoltaics and so on. The efficiencies of single‐junction OSCs have exceeded 19%, making the commercialization of OSCs brighter. Large‐area printing fabrication is a key way to the commercialization of OSCs, and solution‐processed thickness‐insensitive cathode interlayers (CILs) are urgently needed for large‐area printing fabrication. High electron mobility of cathode interfacial materials (CIMs) is critical to enable thickness‐insensitive CILs. N‐type self‐doped characteristics can endow organic CIMs with high electron mobility. Different type of n‐type self‐doped CIMs show different applicability in conventional OSCs and inverted OSCs. External n‐type dopants can further increase electron mobility of hybrid blends. Particularly, ZnO doped with organic dyes can achieve superior photoconductivity in inverted OSCs. This review focuses on solution‐processed thickness‐insensitive CILs for high‐performance OSCs. In conventional OSCs, n‐type self‐doped small molecules and polymers, and external n‐doped hybrid blends as thickness‐insensitive CILs are summarized. In inverted OSCs, n‐type self‐doped small‐molecular electrolytes and polyelectrolytes, PEI‐/PEIE‐based polyelectrolytes, and external n‐doped hybrid blends (including organic‐organic and ZnO‐organic) are summarized for thickness‐insensitive CILs. The relationships between particular functions of CILs and chemical structures of CIMs are highlighted. Finally, summary and outlook of solution‐processed thickness‐insensitive CILs are provided.