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. This study explores the balance between OVC formation and the GGI gradient in CIGSe through Cs and K doping via sputtered CuGa:KF and CuGa:CsF precursors. A scalable, industry-compatible approach for improving CIGSe solar cell performance, achieving cell efficiency exceeding 17 %. • Alkali-doped targets enable scalable CIGSe control and efficiency gains. • Cs doping creates steep Ga profiles and effectively blocks Na diffusion. • The ordered vacancy compound profiles are tailored by dual alkali metal doping and explained by first-principles calculations.