Above 15% Efficient Directly Sputtered CIGS Solar Cells Enabled by a Modified Back-Contact Interface

The Schottky back-contact barrier at the Mo/Cu(In,Ga)Se₂ (CIGS) interface is one of the critical issues that restrict the photovoltaic performance of CIGS solar cells. The formation of a MoSe₂ intermediate layer can effectively reduce this back-contact barrier leading to efficient hole transport. However, the selenium-free atmosphere is unfavorable for the formation of the desired MoSe₂ intermediate layer if the CIGS films are prepared by the commonly used direct sputtering process. In this work, high-efficiency CIGS solar cells with a MoSe₂ intermediate layer were fabricated by the direct sputtering process without a selenium atmosphere. This is enabled by an intermediate CIGS layer deposited on the Mo substrate at room temperature before being ramped to a high temperature (600 °C). The room-temperature-deposited amorphous CIGS intermediate layer is Se rich, which reacts with the Mo substrate and forms very thin MoSe₂ at the interface during the high-temperature process. The formed MoSe₂ decreased the CIGS/Mo barrier height for better hole transport. Consequently, the CIGS solar cell with an 80 nm intermediate layer achieved a power conversion efficiency of up to 15.8%, which is a benchmark efficiency for the direct sputtering process without Se supply. This work provides the industry a new approach for commercialization of directly sputtered CIGS solar cells.