Photoluminescence characterization of a high-efficiency Cu2ZnSnS4 device

We report on low-temperature (4 K) photoluminescence of an 8.3% efficient Cu2ZnSnS4 photovoltaic device. Measurements were recorded as a function of excitation intensity, and the evolution of the resulting spectra is discussed. The spectra indicate that the radiative recombination is characteristic of heavily compensated material with a high quasi donor-acceptor pair density, as determined by the relationship between peak height, peak position, and excitation intensity, as well as the carrier lifetimes at different wavelengths. The blue-shift of the defect-derived peak position is used to estimate the quasi donor-acceptor pair spacing and density. The data indicate an average pair spacing of roughly 3.3 nm, yielding an overall total radiative-defect density of ∼1.3 × 1019 cm−3.