Solution-Processed Tungsten Oxide as an Effective Anode Buffer Layer for High-Performance Polymer Solar Cells

WO₃ is an effective anode buffer layer to substitute PEDOT:PSS in both organic light-emitting diodes and polymer solar cells (PSCs). However, the vacuum deposition of the WO₃ layer is not compatible with low-cost solution-processing technology for the roll-to-roll fabrication of PSCs. Here, we report, for the first time, a solution-processed WO₃ (s-WO₃) anode buffer layer that was prepared by spin-coating tungsten­(VI) isopropoxide solution on an ITO electrode and then thermal annealing at 150 °C for 10 min in air, for the application in PSCs. The s-WO₃ layer shows a high hole mobility of 9.4 × 10^–3 cm²/V·s and high light transmittance. The photovoltaic performance of the buffer layer was investigated by fabricating the PSCs based on poly­(3-hexylthiophene) (P3HT) as a donor and (6,6)-phenyl-C₆₁-butyric acid methyl ester (PC₆₀BM), (6,6)-phenyl-C₇₁-butyric acid methyl ester (PC₇₀BM), indene-C₆₀ bisadduct (IC₆₀BA), or indene-C₇₀ bisadduct (IC₇₀BA) as an acceptor. The PSCs with the s-WO₃ anode buffer layer show enhanced photovoltaic performance in comparison with the devices with PEDOT:PSS as the anode buffer layer. The power conversion efficiency of the PSC based on P3HT/IC₇₀BA with the s-WO₃ anode buffer layer reached 6.36% under the illumination of AM 1.5G, 100 mW/cm². The results indicate that s-WO₃ is a promising solution-processable anode buffer layer material for high-efficiency PSCs and for the fabrication of flexible PSCs