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.