Improving the efficiency of Cu2ZnSn(S, Se)4 solar cells by post-heating treatment precursor films

•The post-heating treatment (PHT) precursor films were adopted to modify the morphology significantly.•The research results indicate that proper PH treatment can modify the surface morphology of precursor films, which is crucial for preparing high-quality absorber layers, the optimum PH temperature was 60 °C.•The best efficiency of the fabricated CZTSSe solar cell is 11.07%, with Voc of 504.6 mV, Jsc of 37.69 mA/cm2, and FF of 58.19% In the solution method, the surface morphology characteristic of the precursor film is essential for obtaining the high quality of the absorber layer. Herein, the post-heating treatment (PHT) precursor films were adopted to modify the morphology significantly and the effects of different PHT temperatures on the properties of precursor films, absorber layer films, and photovoltaic devices were investigated. The precursor film with a more porous surface could be obtained by PHT, which facilitates the downward diffusion of Se easily during sulfoselenization and the formation of a large-grain-spanning monolayer structure. Furthermore, the Cu2ZnSn(S, Se)4 absorber layer surface holes were significantly reduced, owing to sufficient grain growth during sulfoselenization. As a result, the device efficiency with PHT was increased to 11.07% mainly due to improved Cu2ZnSn(S, Se)4 absorber spectral response. This study might provide a new potential method for adjusting precursor film morphology and thus enhancing the corresponding device performance.