Efficiency enhancement of top-illuminated ITO-free organic solar cells using plasmonic-assisted nanostructured reflective electrodes

A nanostructured back reflective electrode with nanobowl-shaped 2D nanohole arrays made from a polystyrene (PS) nanosphere template was developed for enhancing the efficiency of top-illuminated organic solar cells with MoOx (10 nm)/Ag (10 nm)/MoOx (25 nm) stacks as transparent electrodes. The high-performance top electrode with a transmittance of 88.05% at 550 nm and a sheet resistance of 5.93 Omega sq(-1) reached an extremely high figure of merit (sigma(dc)/sigma(opt) = 484). Incorporating plasmonic-assisted electrodes into a poly(3-hexylthiophene):[6,6]-phenyl-C-61-butyric acid methyl ester (P3HT:PC61BM) blend system increased the cell efficiency from 2.91% to 3.35% compared with devices using a planar back electrode. We attributed the efficiency enhancement to the substantial scattering of back-reflected light and enhanced near-field absorption in the proximity of nanoholes.