Record efficient upconverter solar cell devices with optimized bifacial silicon solar cells and monocrystalline BaY2F8:30% Er3+ upconverter

In this paper, we investigate Er3+-doped monocrystalline BaY2F8 as an upconverter material for crystalline silicon solar cells with the aim of making use of previously not-utilized sub-bandgap photons. Monocrystalline samples with 10%, 20% and 30% Er3+ doping were grown in a Czochralski furnace and subsequently attached to an adapted planar bifacial silicon solar cell with a 33.4 mA/cm2 short-circuit current density under one-sun AM1.5G standard measurement conditions. Optical characterization revealed that for the investigated illumination conditions the 30% Er3+-doped samples showed the most promising properties, with a very high peak absorption coefficient of 45.1 cm−1 at 1493 nm and a high external (internal) upconversion quantum yield of 9.5±0.7% (10.1±1.6%) under 4740±250 W m−2 monochromatic irradiation at 1520 nm. Solar simulator measurements of the upconverter solar cell device using the BaY2F8:30% Er3+ sample showed an additional short-circuit current density due to upconversion DjSC,UC of 17.2±3.0 mA/cm2 at an illumination with a solar concentration of 94±17 suns, equivalent to a record relative enhancement of the short-circuit current of 0.55±0.14%. This value constitutes to our knowledge more than a doubling compared to the previously highest published values and more than a 35-fold increase compared to values published three years ago.