Defect Engineering for Efficient Cu_2ZnSnS_4 Solar Cells via Moisture-Assisted Post- Deposition Annealing

摘要

Sulfide kesterite Cu_2ZnSnS_4 (CZTS) solar cells, containing earth-abundantand environmentally benign constituents, are regarded as promising candidatesfor thin-film photovoltaic technologies. CZTS device performance,however, is currently limited by severe nonradiative recombination caused byabundant deep-level defects. Herein, an effective defect engineering approachfor high bandgap CZTS solar cells using a newly introduced moisture-assistedpost-deposition annealing treatment is reported. This treatment modifiesthe local chemical composition within the heterojunction and CZTS grainboundaries and enhances the incorporation of Cd within the CZTS layerduring CdS deposition. Cd not only accumulates at the grain boundaries,but it also presents in grain interiors where it occupies Cu lattice sites. Theoverall modification of the local chemical environment suppresses deep leveldefects and activates relatively shallow acceptor CuZn antisites and Cu vacancies,giving rise to remarkably improved device performance. This work opensa new direction for defect engineering of kesterite materials, which may alsobe applicable to other thin film semiconductors.