In-depth photoluminescence analysis of Cu₂GeS₃ microcrystals under pulsed and continuous-wave excitation

Abstract In this study, an in-depth photoluminescence (PL) analysis of Cu 2 GeS 3 microcrystals under pulsed and continuous-wave (CW) excitation is performed to explore the optical properties and defect structure of this promising novel absorber material for indoor photovoltaics. A rich low-temperature ( T = 8 K) PL spectra with multiple peaks was detected by both excitation sources and analyzed in detail. The edge emission, including free and bound excitons as well as unique trion emission at 1.575 eV, which becomes dominant under the pulsed laser excitation, enabling clear detection of its properties. At higher temperatures also band-to-band emission is observed under the CW excitation, and the donor-acceptor pair recombination with its phonon replica is dominating the PL spectra revealing a shallow donor defect with an ionization energy of 35 meV and a slightly deep acceptor defect with an ionization energy of 119 meV. In addition, from the temperature dependencies of the PL peaks, an extremely weak electron-phonon coupling in CGS was found. The observed edge emission and detected rather shallow defects emphasize the high crystalline quality and the suitability of Cu 2 GeS 3 for photovoltaic applications.