High Efficiency Kesterite Solar Cells Through a Dual Treatment Approach: Improving the Quality of both Absorber Bulk and Heterojunction Interface

Abstract

Cu2ZnSn(S,Se)4 (CZTSSe) solar cells, composed of earth-abundant materials, face challenges in achieving high power conversion efficiency (PCE) due to non-radiative recombination. The limitations primarily stem from the prevalence of CuZn-related and SnZn-related defects in the bulk of the absorber and at the heterojunction interface region. To overcome these challenges, a dual treatment approach is proposed that involves Ag-alloying in the bulk and Al2O3 atomic layer deposition (ALD) process at the p–n interface. Comprehensive characterizations of the fabricated devices reveal that Ag-alloying leads to a substantial reduction in deep defects within the bulk, while Al2O3 ALD process facilitates the formation of a well-defined p–n interface region, along with the defect passivation. This synergetic effect enables PCE enhancement accompanied by the improvements of all device parameters. Notably, devices subjected to the additional Al2O3 ALD process exhibit a substantial improvement in fill factor, which is found to be consistent with a reduced element intermixing width at the p–n heterojunction region. Due to improvements in both the bulk absorber and the heterojunction, the highest PCE of 13.33% is achieved without an anti-reflection coating. © 2023 Wiley-VCH GmbH.