Spontaneous and stimulated emission in thin films of Cu(In$_{1-x}$Ga$_{x}$)(S$_{y}$Se$_{1-y}$)$_{2}$ solid solutions in the сomposition of solar cells

The results of a study of the emission spectra of thin nanocrystalline films of Cu(In$_{1-x}$Ga$_{x}$)(S$_{y}$Se$_{1-y}$)$_{2}$ direct-band-gap solid solutions in the structure of solar cells at $\sim$0.5 W/cm$^2$ continuous wave and nanosecond pulsed laser excitation in the range of excitation power density 0.1 – 53 kW/cm$^2$ and temperatures of 10–300 K are presented. It was found that stimulated emission (SE) occurs in thin CIGSSe films in the temperature range from 10 K to 90 K in the spectral region $h\nu$ = 1.062 – 1.081 eV with a minimum threshold pump level of about 1 kW/cm$^2$. It was shown, that, with increasing intensity of the exciting emission, the spontaneous emission bands shift toward higher energies. It was found that the photoluminescence bands at low excitation levels and the SE bands shift with increasing temperature toward higher energies, and the PL bands at high excitation levels shift toward low energies. Possible causes and mechanisms of the influence of temperature and excitation intensity on the spectral positions of spontaneous and SE of the films of solid solutions are discussed.