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

WO 3 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 WO 3 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 WO 3 (s-WO 3 ) 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-WO 3 layer shows a high hole mobility of 9.4 × 10 –3 cm 2 /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-C 61 -butyric acid methyl ester (PC 60 BM), (6,6)-phenyl-C 71 -butyric acid methyl ester (PC 70 BM), indene-C 60 bisadduct (IC 60 BA), or indene-C 70 bisadduct (IC 70 BA) as an acceptor. The PSCs with the s-WO 3 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/IC 70 BA with the s-WO 3 anode buffer layer reached 6.36% under the illumination of AM 1.5G, 100 mW/cm 2 . The results indicate that s-WO 3 is a promising solution-processable anode buffer layer material for high-efficiency PSCs and for the fabrication of flexible PSCs.