Improved Inverted Organic Solar Cells With a Sol–Gel Derived Indium-Doped Zinc Oxide Buffer Layer

We studied sol-gel derived indium-doped zinc oxide (IZO) with various indium contents as a functional buffer layer in inverted polymer:fullerene bulk-heterojunction solar cell. The short-circuit current density was observed to increase by doping indium in pure ZnO buffer layer. The maximum current density was obtained with a 1 at.% indium doping. Although the open-circuit voltage and fill factor reduced slightly, the inverted organic solar cell with 1 at.% IZO buffer layer showed a power conversion efficiency of 3.3%, which is higher compared to that (2.94%) of the device with undoped ZnO buffer layer under illumination of AM1.5G. The better performance is due to combined effects of improvement in charge collection and higher optical transmittance of electrode/buffer layer stack.