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 degrees C for 10 min in air, for the application in PSCs. The s-WO3 layer shows a high hole mobility of 9.4 x 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 (PC60BM), (6,6)-phenyl-C-71-butyric acid methyl ester (PC70BM), indene-C-60 bisadduct (IC(60)BA), or indene-C-70 bisadduct (IC(70)BA) 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/IC(70)BA with the s-WO3 anode buffer layer reached 6.36% under the illumination of AM 1.5G, 100 mW/cm(2). 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.