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.