Optimum Electrical and Optical Properties of Transparent Conducting Oxide for Cu(In,Ga)Se2 Photovoltaic Module Applications

Abstract

Herein, the transparent conducting oxide (TCO) characteristics of the window layer as a factor in the decrease of conversion efficiency from lab‐scale cells to modules are focused on. Then, an optical model and a circuit model are constructed based on measured data, and TCO parameters are investigated to optimize Cu(In,Ga)Se2 (CIGS) module characteristics. Simulations assuming ZnO:Al and ZnO:B as the TCO, which are commonly used in CIGS modules with a substrate structure, show that the range of the TCO parameters to obtain high efficiency is limited. In particular, the optimum values of module characteristics are separated into high‐carrier density/thin‐film region with a smooth surface and low‐carrier density/thick‐film region with a textured surface for the TCO layer. In addition, simulations assuming a high‐mobility TCO and a wide‐gap CIGS absorber to boost conversion efficiency reveal that the wide‐gap CIGS absorber mitigates the effects of resistance losses and free carrier absorption due to the TCO, thereby expanding the design range of the carrier density in the TCO layer.