Scalable cesium/potassium incorporation via CuGa:CsF/KF precursors enables high-efficiency selenized CIGSe solar cells

This study explores the incorporation of alkali metals into Cu(In,Ga)Se 2 (CIGSe) thin films using CuGa:KF and CuGa:CsF sputtering targets, demonstrating their compatibility and scalability with industrial sequential processes without requiring any additional post-deposition treatment. The introduction of alkali metals through CuGa:KF and CuGa:CsF precursors significantly influences the compositional gradient, ordered vacancy compound (OVC) distribution, and cell performance. Ab initio calculations reveal a link between steeper Ga gradients and OVC formation. Co-doping with Cs and K, using a stacked precursor layer of sputtering CuGa:KF/CuGa:CsF targets, further optimizes the Ga gradient and reduces OVC formation at the backside of CIGSe. These effects collectively enhance cell performance, achieving an efficiency exceeding 17 %, even with low-reactivity Se vapor during selenization. This approach offers a new direction for simplifying heavy alkali metal incorporation and eliminates the need for post-deposition treatments. Importantly, it is fully compatible with existing industrial fabrication processes and provides a scalable pathway for high-efficiency selenized CIGSe production.