ZnO:Al textured films for improved performance in organic photovoltaics

Abstract

A major issue in organic photovoltaics (OPVs) is the poor mobility and recombination of the photogenerated charge carriers. The active layer has to be kept thin to facilitate charge transport and minimize recombination losses. However, optical losses due to inefficient light absorption in the thin active layers can be considerable in OPVs. Therefore, light trapping schemes are critically important for efficient OPVs. In this paper, high efficient OPVs are demonstrated by introducing randomly nanostructured front electrodes, which are fabricated using commercially available ZnO:Al (AZO) films by means of a wet etching method. The etched AZO front electrode induces strong diffusion and scattering of the incident light, leading to the efficient light trapping within the device and enhancement of light absorption in the active layer. Such a nanostructured electrode can achieve an improved device performance by maintaining simultaneously high open-circuit voltage and fill factor values, while providing excellent short-circuit current enhancement through efficient light trapping. The best device obtained based on the textured electrode shows a 11.29% improvement in short current density and a 8.17% improvement in power conversion efficiency, as compared with the device with a flat electrode. The improvement in PCE is directly correlated with the enhancement of light absorption in the active layer due to the light scattering and trapping effect induced by the randomly nanotextured electrodes, which is confirmed by a haze factor measurement and an external quantum efficiency characterization. The well-established contact interfaces between the etched electrodes and active layers are made, and thus reduce the impact on the open-circuit voltage and fill factor values in OPVs. We thus conclude that the method of light manipulation developed in this paper will provide a promising and practical approach to fabricate high-performance and low-cost OPVs.