Performance of Inverted Organic Solar Cells via Thickness Control of ZnO Thin Films

For film thickness control, zinc oxide (ZnO) thin films were deposited by radio-frequency (RF) magnetron sputtering system on an indium tin oxide (ITO)-coated glass substrate with a pure ZnO target. The crystallinity nanostructure and surface morphology of the ZnO thin films were investigated by X-ray diffraction (XRD) and, scanning electron microscopy (SEM). With low coverage of the ZnO thin films, the grain size and surface roughness increased. We also studied the optical-electrical properties of the ZnO thin films such as carrier concentration, mobility, and resistivity by Hall measurement. As the coverage of the ZnO thin films increased, the concentration increased, but the mobility and resistivity decreased. Inverted organic solar cells (IOSE) with low coverage exhibited a short circuit current (J(sc)) of 6.2 mA/cm(2), open circuit voltage (V-oc) of 0.41 V and fill factor (FF) of 0.36 with an overall conversion efficiency of 1.98%.