Strengthening the Properties of Earth-Abundant Cu₂ZnSn(S,Se)₄ Photovoltaic Materials via Cation Incorporation with Ni

The Cu2NixZn1–xSn(S,Se)4 (0 ≤ x ≤ 0.1) (CNZTSSe) film absorbing layer materials were successfully prepared by sol–gel means and post selenization technique. The experimental results show that the crystal quality, photoelectric properties, and device efficiency of the film can be improved by Ni doping. The grain size and crystallinity of the films significantly increase by adjusting the doping content of Ni. When x = 0.05, crystallinity and grain size reach the optimum value, and the film surface is smooth and compact. Meanwhile, Ni has successfully replaced the Zn site in the crystal lattice, which reduces the formation of harmful defects related to Zn and improves the electrical properties of the films. The hole concentration of the film is 5.03 × 1014 cm–3, and the maximum Hall mobility of the film is 8.95 cm2 V–1 s–1 under the optimum Ni doping content (x = 0.05). In addition, the continuously tunable band gap (Eg) was obtained, which decreases continuously from 1.17 to 1.08 eV. Compared with the pure Cu2ZnSn(S,Se)4 (CZTSSe) solar cell, the open circuit voltage (VOC) of the CZNTSSe (x = 0.05) device was increased by 42 mV, and the power conversion efficiency was boosted from 3.61 to 5.32%.