A Study on the Effects of Selenization Temperature on the Properties of Na-Doped CuZnSn(S,Se) Thin Film and Its Correlation with the Performance of Solar Cells.

In this study, we prepared Na-doped CuZnSn(S,Se) [noted as (NaCu)ZnSn(S,Se)] films on the Mo substrate using a simple and cheap sol-gel method together with the post-annealing technique. The effects of selenization temperature on the properties of Na-doped CuZnSn(S,Se) were surveyed. The results indicated that some sulfur atoms in the films were substituted by selenium atoms by increasing the selenization temperature, and all films selenized at different temperatures had a kesterite structure. As the selenization temperature increased from 520 to 560 °C, the band gaps of the film can be tuned from 1.03 to 1 eV. The film with better morphology and opto-electrical properties can be obtained at an intermediate selenization temperature range (e.g., 540 °C), which had the lowest resistivity of 47.7 Ω cm, Hall mobility of 4.63 × 10 cm/Vs, and carrier concentration of 2.93 × 10 cm. Finally, the best power conversion efficiency (PCE) of 4.82% was achieved with an open circuit voltage (Voc) of 338 mV, a short circuit current density (Jsc) of 27.16 mA/cm and a fill factor (FF) of 52.59% when the selenization temperature was 540 °C.