Thin film solar cell with 8.4% power conversion efficiency using an earth‐abundant Cu₂ZnSnS₄ absorber

Using vacuum process, we fabricated Cu₂ZnSnS₄ solar cells with 8.4% efficiency, a number independently certified by an external, accredited laboratory. This is the highest efficiency reported for pure sulfide Cu₂ZnSnS₄ prepared by any method. Consistent with literature, the optimal composition is Cu‐poor and Zn‐rich despite the precipitation of secondary phases (e.g., ZnS). Despite a very thin absorber thickness (~600 nm), a reasonably good short‐circuit current was obtained. Time‐resolved photoluminescence measurements suggest a minority carrier‐diffusion length on the order of several hundreds of nanometers and relatively good collection of photo‐carriers across the entire absorber thickness. Copyright © 2011 John Wiley & Sons, Ltd.