Tb3+–Er3+ couples as spectral converters in NaYF4 for GaAs solar cells

Abstract

In order to reduce the thermal loss due to spectral mismatch of solar cell absorption, the quantum cutting with Tb3+–Er3+ couples as spectral converters is experimentally observed. One high-energy ultraviolet photon (Tb3+ 7F6 → 5L1) is quantumly cut into two lower energy photons: one in the near-infrared region (Er3+ 4I9/2 → 4I15) and the other in the blue region (Tb3+ 5D4 → 7F6), both of which can be efficiently absorbed by solar cells. A quantum efficiency, ηQE, of up to 188% is calculated, which is close to the theoretical limit of 200%. The energy mismatch in the energy transfer from Tb3+ (5L1 → 5D4) to Er3+ (4I9/2 → 4I15/2) is 237 cm−1, less than the phonon energy of 400 cm−1 in NaYF4, making the energy transfer nearly resonant. The energy migration among Tb3+ donors is treated approximately by the diffusion model and the initial process of energy transfer among the Tb3+–Er3+ couples is found to be dipole–dipole interactions.