ZnO–Ag–MoO3 transparent composite electrode for ITO-free, PEDOT: PSS-free bulk-heterojunction organic solar cells

We report on the electrical and optical properties of ZnO/Ag/MoO3 (ZAM) multilayer electrodes deposited directly on glass substrates by a combination of radio frequency (RF) and direct current (DC) sputtering for bulk-heterojunction organic solar cells (OSCs). Compared to indium tin oxide (ITO) electrodes showing 20 Ω/sq, the transparent composite electrodes (TCE) in this study exhibited very low sheet resistance of 5 Ω/sq without post annealing. In addition, as a hole transport layer, the MoO3 performed with a higher fill factor than PEDOT:PSS due to lower series resistance, resulting in a power conversion efficiency of 2.3%, Voc of 0.59 V, and Jsc of 9 mA/cm2. The power conversion efficiency of the OSC with the ZAM electrode is lower than that of organic solar cells on ITO which has 3.3% efficiency, due to lower transmittance after MoO3 layer deposition. However, our results do support the possibility of using MoO3 as both Ag protecting and hole transport layers for indium-less and PEDOT:PSS-less bulk-heterojunction OSCs.