Efficiency enhancement of single-junction GaAs solar cells coated with europium-doped silicate-phosphor luminescent-down-shifting layer

In this study, we investigated the electrical and optical performance of single-junction GaAs solar cells coated with an antireflective layer of indium tin oxide (ITO) via thermal sputtering deposition followed by a layer of SiO2 doped with 3 wt% europium-doped (Eu-doped) silicate phosphors via spin-on film technique. The chemical composition of the Eu-doped silicate phosphors was analyzed using energy-dispersive X-ray spectroscopy and the luminescent downshifting (LDS) characteristics were examined in terms of photoluminescence, optical reflectance, and external quantum efficiency (EQE) response. Reverse saturation-current and ideality factor were used to evaluate the passivation performance of ITO films thermal sputtered on GaAs solar cells. The antireflective performance of the ITO film and the LDS effects of the Eu-doped silicate phosphor coatings were respectively evaluated in terms of optical reflectance and EQE response. The enhancement of photovoltaic performance due to LDS effects was confirmed by photovoltaic current density-voltage characteristics of cells under one-sun air mass 1.5G solar simulations. The efficiency enhancement of the cell with only an ITO/SiO2 antireflective layer was 18.39%, whereas the cells coated a SiO2 layer that included various species of Eu-doped phosphors (species-A, species-B, or species-C) on ITO achieved efficiency enhancements of 19.83%, 20.29%, and 21.07%, respectively.