Thermally evaporated Se, including the molecules of Se 2 , Se 5 , Se 6 , Se 7 , and Se 8 in the vapor at 550–600 °C, is widely used for the selenization of CZTSSe films. However, active small-molecule Se 2 tends to form large clusters of Se atoms at saturation vapor pressure, resulting in the large Se deficiency and poor crystallization of CZTSSe films. To regulate the time for Se to reach saturation vapor pressure and promote the role of active small-molecule Se, the evaporation area of Se is controlled. Then the corresponding grain growth mechanism of CZTSSe films and device efficiency are systematically investigated. The results demonstrate that the appropriate evaporation area of Se can not only optimize the time for Se vapor to reach saturation, promote the rapid reaction crystallization between the precursor films and active Se 2 , but also inhibit the nucleation at the CZTSSe/Mo interface, thus making the CZTSSe films show a perfect top-down grain growth mode. By preliminary optimization, when the evaporation area of Se is 245 mm 2 , a large-grain spanning monolayer CZTSSe thin film is obtained; meanwhile, a device with a high efficiency of 12.39% is achieved. This study provides a new selenization strategy for improving the crystallinity of CZTSSe thin films.
High-crystalline-quality absorbers with fewer defects are crucial for further improvement of open-circuit voltage ( V OC ) and efficiency of Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells. However, the preparation of high-quality CZTSSe absorbers remains challenging due to the uncontrollability of the selenization reaction and the complexity of the required selenization environment for film growth. Herein, a novel segmented control strategy for the selenization environment, specifically targeting the evaporation area of Se, to regulate the selenization reactions and improve the absorber quality is proposed. The large evaporation area of Se in the initial stage of the selenization provides a great evaporation and diffusion flux for Se, which facilitates rapid phase transition reactions and enables the attainment of a single-layer thin film. The reduced evaporation area of Se in the later stage creates a soft-selenization environment for grain growth, effectively suppressing the loss of Sn and promoting element homogenization. Consequently, the mitigation of Sn-related deep-level defects on the surface and in the bulk induced by element imbalance is simultaneously achieved. This leads to a significant improvement in nonradiative recombination suppression and carrier collection enhancement, thereby enhancing the V OC . As a result, the CZTSSe device delivers an impressive efficiency of 13.77% with a low V OC deficit.
危险品化学品经营许可证（带存储）