Enhancing the performance of CZTSSe solar cells via an alternate spin-coating process with DMSO and DMF

The CZTSSe absorber layer prepared with DMSO exhibits extensive cavities at its bottom, and a prominent double-layer structure is frequently observed within the CZTSSe absorber synthesized using DMF, both of which have a detrimental impact on the device performance. In this paper, an alternate spin-coating process using DMSO and DMF solvent systems is proposed, which eliminates the double-layer structure of CZTSSe and reduces the number of cavities at the bottom of the absorber layer, thereby enhancing its overall quality. This method outperforms the traditional single-solution spin-coating technique by combining the advantages of two solvent systems, allowing for the preparation of an ideal CZTSSe film without disturbing the elemental ratio, ultimately resulting in a single-layer absorber composed of large grains. After three repetitions of an identical alternate spin-coating process, the average grain size of the absorber layer increased from 0.83 to 1.21 μm. This innovative process leads to a reduction in carrier recombination and an improvement in the short-circuit current density, ultimately raising the photoelectric conversion efficiency from 7.40% to 8.88%.