Fabrication of Cu2ZnSnS4 thin film solar cells by annealing of reactively sputtered precursors

The Cu2ZnSnS4 (CZTS) absorbers for thin film solar cells were fabricated by reactive sputtering followed by post-annealing. The effects of annealing temperature and Cu/(Zn + Sn) ratio on the film microstructure and related device performance were systematically investigated. It was found that the higher annealing temperature facilitates Zn incorporation and grains growth, but leads to more Sn loss and thicker MoS2 layer. The CZTS absorbers with a lower Cu/(Zn + Sn) ratio show larger grain size and more ZnS particles on the surface, whereas the films with higher Cu content (Cu/Sn > 2) demonstrate small grain size, much Cu2−xS phases and cracks. The highest device efficiency of 3.72% was obtained from the CZTS film annealed at 570 °C with Cu/(Zn + Sn) ratio of 0.78. The performance of devices is limited by low Jsc and FF due to the interface recombination and the block of carrier transport by ZnS.