Junction electroluminescence of Cu(In,Ga)Se2 devices

The electroluminescence of Cu(In,Ga)Se₂ polycrystalline solar cells produced at different laboratories by different processes and with different Ga contents has been measured as a function of temperature and wavelength. The total emission intensity was found to have a power-law variation with the diode current with an exponent between 1.2 and 1.9. The external quantum efficiency of the electroluminescence was estimated to be between 10^-6 and 10 ^-7 at room temperature and modest currents. This increases by up to two orders of magnitude at 70 K. A commercial light emitting diode (LED) was found to have an external quantum efficiency between 10^-3 and 10^-4 at roughly 10³ higher current densities. Luminescence spectra were Gaussian. The peak luminescence wavelength of the solar cells increases upon cooling while the maximum wavelength for photocurrent generation decreases. The results suggest at least two independent processes for carrier generation and radiative recombination