Amphiphilic fullerenes modified 1D ZnO arrayed nanorods–2D graphene hybrids as cathode buffer layers for inverted polymer solar cells

Abstract

Amphiphilic fullerene-end-capped poly(ethylene glycol) (C60-PEG) is synthesized to modify uniform ZnO arrayed nanorods (ANs) grown in situ on the surface of poly(N-vinyl pyrrolidone) decorated reduced graphene oxide (RGO). The two dimensional (2D) graphene provides a stable and conductive flat substrate for one dimensional (1D) arrayed nanorods with reduced defects. The addition of amphiphilic C60-PEG can improve the compatibility of the cathode buffer layer and the active layer. Moreover, C60-PEG produces a modified efficacy on the arrayed nanorods with reduced defects and decreased work function. Compared to the bare ZnO ANs, the C60-PEG modified ZnO ANs@RGO cathode buffer layer can reduce the recombination of carriers, increase the electron mobility and enhance electron extraction. As a result, the efficiency of the inverted polymer solar cells based on thieno[3,4-b]-thiophene/benzodithiophene (PTB7) : [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) is improved to 8.1% with better long-term stability.