Spin-Coating Se in Precursor to Improve Absorber Crystallinity and Reduce Defects Enabling 13.57% Efficiency for Kesterite Solar Cells

Poor crystallinity is a common problem of kesterite absorbers based on non-hydrazine solution method, which obstructs charge transfer and affects photovoltaic performance of the thin-film devices, especially the open-circuit voltage (VOC). Se diffusion is often insufficient during the crystal growth of kesterite absorber, resulting in uneven selenization reaction. Herein, Se molecule is introduced into kesterite precursor film to promote the absorber crystallinity while preventing the formation of a thick Mo(Se,S)2 layer. It is found that after Se-introduction treatment, Se element distributes more uniformly in the absorber film after high-temperature annealing. During selenization, the lower part of the precursor film can easily obtain Se and experience crystallization, thus promoting the crystallization of the whole absorber. As a result, the absorber defects are passivated. According to charge carrier characterization, the carrier lifetime of the device is prolonged due to the reduced carrier recombination centers. Finally, a champion device with the VOC increases by 23 mV, and an efficiency of 12.39% (active area efficiency of 13.57%) is achieved.