Induced crystallization of sol–gel-derived zinc oxide for efficient non-fullerene polymer solar cells

Abstract

With the rapid development of near-infrared absorbing acceptor materials, the photoelectric conversion efficiency of polymer solar cells (PSCs) has been greatly improved in the past several years. However, serious charge recombination near to the cathode interlayer, like sol-gel derived zinc oxide (sg-ZnO), usually restrains the overall device performance, which is attributed to the mismatch between the relatively poor electron transporting property of the cathode interlayer and the largely increased photocurrent from the widely extended absorbing active layer. In this work, we demonstrate a novel strategy for in situ induced crystallization of zinc oxide (ic-ZnO) that shows increased crystallinity relative to the classic sg-ZnO, and such ic-ZnO is proved to reduce the interfacial charge recombination efficiently in PSCs. The ic-ZnO was synthesized by a heterogeneous nucleation process, using as-synthesized zinc oxide (as-ZnO) nanoparticles as the nucleus in the precursor solution of sg-ZnO. By using this film as efficient electron transporting layer, a power conversion efficiency of 16.62% was achieved in inverted PSCs. Our results clearly indicate that increasing the crystallinity of zinc oxide by in situ induced crystallization is a facile strategy to adapt the demand of high performance non-fullerene PSCs.