Electrostatic Potential Complementarity for Thickness‐Tolerant Cathode Interlayers in High‐Efficiency Organic and Tandem Solar Cells

Designing cathode interlayers (CILs) that simultaneously deliver high efficiency, operational stability, and broad thickness tolerance remains a critical challenge for organic solar cells (OSCs). Herein, trimesic acid (TMA) and phloroglucinol (PG), two small molecules featuring opposite central electrostatic potential (ESP) distributions, are employed as model systems to systematically elucidate their intermolecular interactions with the benchmark CIL material PDINN and to reveal the molecular origin of thickness sensitivity. Benefiting from complementary ESP matching, PG incorporation markedly enhances PDINN self-doping, electrical conductivity, energy-level alignment, and π-π stacking, while suppressing PDINN self-agglomeration and reducing Ag electrode work function. These synergistic effects promote efficient charge extraction and transport and suppress non-radiative recombination losses. As a result, OSCs with the PDINN:PG CIL achieve a power conversion efficiencie (PCE) of 20.0% (certified 19.5%), together with outstanding thickness tolerance, maintaining 87.0% of champion efficiency at 50 nm, and improved operational stability (80% after 600 h). Furthermore, perovskite-organic tandem solar cells (TSCs) deliver a decent PCE of 26.4%. This work establishes an ESP-guided molecular interfacial engineering strategy for thickness-tolerant and durable CILs for next-generation OSCs.