Solution‐processing induced H‐aggregate of Perylene‐Diimide Zwitterion Exhibiting Compact Molecular Stacking toward Efficient Cathode Modification in Organic Solar Cells

High‐performance organic cathode interlayers (CILs) play a crucial role in the advance of organic solar cells (OSCs). However, organic CILs have exhibited inferior performances to their inorganic counterparts over a long time, due to the inherent shortcoming of poor charge transporting capability. Here, we designed and synthesized a perylene‐diimide (PDI) zwitterion PDI‐B as high‐performance organic CIL for OSCs. We revealed that an obvious H‐aggregate of PDI‐B was formed during the solution processing, thereby significantly enhancing the charge transporting capability of the CIL. Compared to the classic PDINN, the π‐π stacking distance of PDI‐B was reduced from 4.2 Å to 3.9 Å, which further facilitated the charge transport. Consequently, PDI‐B showed a high conductivity of 1.81×10−3S/m; this is comparable to that of inorganic CILs. The binary OSC showed an elevated PCE of 19.23%, which is among the highest PCE values for binary OSCs. Benefitting from improved solvent resistance and good compatibility with large‐area processing method of PDI‐B, the photovoltaic performances of inverted and 1‐cm2 OSC were significantly improved. The results from this work provide a new approach of optimizing the condensed structure of PDI film to boost the charge conductivity, opening an avenue to develop high‐performance PDI‐based CILs.