Luminescence properties of III-V multi-junctions solar cells

The recent achievement of multi-junctions solar cells, based on III-V semiconductors, exceeding 43% efficiency, has stimulated a rapid growth of concentration photovoltaic (CPV) technology. The large efficiency of these cells is based on the matching between the semiconductors band gap and the solar spectrum and the capability of working under concentrated illumination, up to ~1000 suns. The research pays, therefore, attention to investigate in detail the mechanisms that affect the conversion efficiency, such as the non radiative losses that increase the cell temperature thus favoring the electron-hole (e-h) recombination. With the aim to clarify the performances of these III-V cells, here we study the optical features of different multi-junctions InGaP/InGaAs/Ge solar cells, of commercial origin; our experiments are based on time-resolved photoluminescence spectra acquired under IR-visible-UV laser excitation. The reported results evidence different contributions due to the e-h radiative recombination of each junction; a band centered around 1.8 eV related to InGaP and another centered around 1.4 eV related to InGaAs, both decaying with a lifetime in the ns time scale.