Solution-processed vanadium oxide as a hole collection layer on an ITO electrode for high-performance polymer solar cells

Abstract

A solution-processed vanadium oxide (s-VO_x) anode buffer layer on an indium-tin-oxide (ITO) electrode was used instead of PEDOT:PSS for improving the stability and photovoltaic performance of the polymer solar cells (PSCs). The s-VO_x layer was prepared by spin-coating a vanadyl acetylacetonate (VO(acac)₂) isopropyl alcohol solution on the ITO electrode and then thermal annealing at 150 °C for 10 min. The s-VO_x oxide layer is highly transparent in the visible range and shows effective hole collection property. The photovoltaic performance of the s-VO_x buffer layer was studied by fabricating the PSCs based on poly(3-hexylthiophene) (P3HT) as an electron donor and four soluble fullerene derivatives, [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₀BM), [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₀BM), indene-C₆₀ bisadduct (IC₆₀BA), and indene-C₇₀ bisadduct (IC₇₀BA), as electron acceptors. The PSCs with the s-VO_x buffer layer show improved performance in comparison with the traditional devices with the PEDOT:PSS buffer layer on ITO, no matter which fullerene derivative was used as an acceptor. The power conversion efficiency of the PSC based on P3HT:IC₇₀BA (1 : 1, w/w) with the s-VO_x anode buffer layer reached 6.35% under the illumination of AM1.5G 100 mW cm⁻².