Effect of Self-Seed Inducing on the Growth Mechanism and Photovoltaic Performance of Cu2ZnSnSe4 Thin Films

The self-seed inducing grain growth mechanism for a Cu2ZnSnSe4 (CZTSe) thin film is explored via the existence of the fine-grain CZTSe synthesized spontaneously at a relatively low soft-selenization temperature of 300 degrees C. Fine control over the elementary proportion and distribution of metal precursors is an important approach for obtaining the self-seed inducing effect after soft selenization. Herein, a multiple-cycle metal stack precursor, prepared by a weighting method, is developed to control the elementary proportion and distribution. By shortening the diffusion distance to produce a self-seed inducing effect at soft selenization, the formation of detrimental intrinsic defects and secondary phases is effectively suppressed, contributing to the optimization of the CZTSe absorber back contact and surface. Consequently, the conductivity of the grain interiors and boundaries of the absorber layer is enhanced, the electric potential and roughness of the surface are reduced considerably, and the minority carrier lifetime of the layer is increased. When the number of stacked cycles increases from 1 to 7, the champion efficiency of CZTSe solar cell improves from 2.97% to 8.05% with a significant decrease in the open circuit voltage deficit from 0.831 to 0.617 V. These results may prove useful for developing a wider range of multinary compound semiconductor devices.