Dominant Face‐On Oriented Perylene‐Diimide Interlayers for High‐Performance Organic Solar Cells

Electron transport properties of cathode interlayers are crucial to high‐performance organic solar cells (OSCs). We propose a novel approach to enhance electron transport of cathode interlayers through controlling a preferential face‐on molecular orientation of non‐ionic perylene‐diimide‐ (PDI) based cathode interlayers with restricted n‐doping effects. 1‐(2,5,8‐trioxadec‐10‐yl)‐1,2,3‐triazole (TOT) units as bulky and extended side chains were incorporated into brominated‐PDIs via click chemistry to yield PDIBr‐TOT. TOT side chains impart PDI‐based interlayers with a dominant face‐on orientation, meanwhile leading to a negligible doping effect due to their weak electron‐donating properties. Impressively, at a slight doping level, higher electron mobility is gained through efficient vertical charge transport channels built by preferred face‐on molecular orientations of PDIBr‐TOT, beating the results acquired through strong doping effects of traditional PDIBr‐N with an edge‐on orientation. Thus, PDIBr‐TOT can suppress exciton recombination and lower the surface energies for good contact with active layers, consequently leading to increases in fill factor and short‐circuit current. Integrating PDIBr‐TOT with various active layers, a remarkable efficiency of 19.52% is obtained. Moreover, device stability is enhanced by restrained doping effects. Modulating face‐on orientations of cathode interlayers prescribed here will encourage further innovative designs of high‐performance cathode interlayers towards OSC advances.