Chemical composition dependence of photoluminescence from Cu2ZnSnS4 thin films with potential fluctuations

Abstract

The temperature and excitation intensity dependence of photoluminescence (PL) spectra from Cu2ZnSnS4 (CZTS) thin films with various chemical compositions was investigated. Three types of CZTS thin films were examined: Zn‐rich (group A), Cu‐ and Zn‐poor (group B), and Cu‐rich and Zn‐poor (group C). Groups A, B, and C gave PL spectra with peaks at around 1.2, 1.30, and 1.45 eV, respectively. These spectra exhibited large peak energy shifts to higher energies as the excitation intensity increased by more than 10 meV/decade due to potential fluctuations. The PL spectra of groups A and B can be attributed to band‐to‐impurity luminescence, and the origin of the spectra was found to be CuSn and VZn or [VZn + SnZn], respectively. The potential fluctuations were estimated from the lower energy side of the PL spectra, and the Cu‐poor samples exhibited smaller potential fluctuations.