Improving the performance of solution-based CZTSSe absorber by selenization annealing with selenium powder in argon

Due to the low toxicity and abundance of nature, Cu2ZnSn(S,Se)(4) (CZTSSe) has been considered as a promising solar cell material. The absorber is the most critical structure in a solar cell, which determines the performance of the cell. Selenium-rich CZTSSe can be formed by replacing S atoms of CZTS with Se. However, the method of adding Se element through H2Se is constrained due to the toxicity of H2Se. The work adopted a method to prepare excellent CZTSSe absorbers without H2Se. The stack structure CZTS precursor films were prepared by solution-based deposition, and CZTSSe absorbers were obtained after selenization annealing at 550 degrees C with 0.1, 0.2 and 0.3 g of selenium powders in argon, respectively. The obtained CZTSSe absorbers had pure CZTSSe phase, high absorption coefficients and appropriate bandgaps. After annealing with 0.2 g of selenium powder, the holes in the CZTSSe film diminished, and the grain size of absorbers increased from 0.31 mu m in the CZTS absorber to 1.17 mu m. The peaks of Se 3d for CZTSSe absorber were observed, the lattice spacing of plane (112) increased from 3.10 & Aring; to 3.22 & Aring;, and the work function decreased from 5.31 eV to 5.19 eV. The improved performance of absorber will be of great significance for the efficiency of CZTSSe device.