Uncovering novel photoluminescence characteristics of Cu2ZnSnS4 thin-film solar cells through pulsed laser excitation

Photoluminescence (PL) spectroscopy under pulsed laser excitation was employed to investigate the recombination mechanisms in a Cu2ZnSnS4 (CZTS) thin-film solar cell over a temperature range of 8–300 K. The PL spectra revealed one asymmetric band at 1.27 eV at T = 8 K, which was successfully fitted using an asymmetric double sigmoidal shape, indicating spatial variations in localized states and bandgap fluctuations. The PL band exhibited a temperature-dependent blue shift (∼0.26 meV/K) and low thermal activation energy (∼22 meV), suggesting recombination involving closely spaced deep donor–deep acceptor pairs. Laser power-dependent PL measurements at 8 K showed a pronounced blue shift of approximately 31 meV per decade of laser power, attributed to a band-filling effect under high excitation densities. The results support a model in which recombination occurs near band-bending regions. This study highlights the sensitivity of pulsed laser excitation PL, revealing previously unresolved recombination dynamics and localized states in CZTS-based photovoltaic materials.