Rapid thermal annealed WO3-doped In2O3 films for transparent electrodes in organic photovoltaics

Abstract

We investigated the effect of rapid thermal annealing (RTA) on the electrical, optical, structural and surface properties of WO3-doped In2O3 (IWO) films for use in organic solar cells (OSCs). Increasing the RTA temperature led to significant decreases in resistivity and sheet resistance due to activation of the W dopants and the (2 2 2) preferred orientation of the IWO films. At the optimized RTA temperature of 500 °C, the IWO film had a sheet resistance of 21 Ω/square and an optical transmittance of 89.39%, which is comparable to conventional ITO electrodes. Due to the high mobility of 46 cm2 V−1 s−1, the IWO film showed a higher optical transmittance in the near infrared wavelength region even though it had a low resistivity of 4.34 × 10−4 Ω cm. Furthermore, the 500 °C annealed IWO film showed very smooth surface morphology due to its (2 2 2) preferred orientation. The performance (fill factor of 61.59%, short circuit current of 8.84 mA cm−2, open circuit voltage of 0.60 V and power conversion efficiency of 3.27%) of the OSC fabricated with the IWO electrode was nearly identical to that of the OSC with a reference ITO anode, indicating that the IWO anode is a promising high-mobility transparent electrode material to replace conventional ITO anodes for high-performance OSCs.