Ag Precursor-Assisted 350 °C Growth of Cu(In,Ga)Se2 Solar Cells Based on a Three-Stage Process

Abstract Lowering the growth temperature of Cu(In,Ga)Se2 (CIGS) is required for bifacial structures based on CIGS deposition on transparent conductive oxides and for CIGS tandem solar cells, but low-temperature growth generally deteriorates CIGS absorber quality and solar-cell performance. To address this issue, we introduce Ag as a precursor layer for low-temperature CIGS growth. We first vary the Ag precursor thickness to identify the optimum Ag incorporation level. Although Ag improves CIGS absorber quality, it also reduces the net acceptor density; excessive Ag incorporation therefore leads to performance loss. To balance these competing effects, we select a 10-nm Ag precursor thickness, which improves film quality while limiting the reduction in net acceptor density, and apply this condition to low-temperature growth. Under this optimized condition, Ag incorporation improves the quality of low-temperature-grown CIGS absorbers, as evidenced by the minority-carrier lifetime, diode parameters, and Urbach energy, consistent with its behavior under the reference high-temperature condition of 600 °C. As a result, (Ag,Cu)(In,Ga)Se2 solar cells fabricated at 350 °C maintain a power conversion efficiency of approximately 15%, whereas CIGS devices without Ag show severe performance degradation. These results demonstrate that Ag precursor engineering is effective for low-temperature CIGS growth toward bifacial and tandem solar-cell applications.