Figure 1: Thermal up-conversion with hot carriers: concept and implementation.
(a) Energy flow showing solar photons entering the solar cell (Nsun) and sub-bandgap photons (NIR) entering the solar collector. The solar collector generates hot carriers and emits broadened PL (Nup) towards the solar cell. The additional flux of above-gap photons, which have been thermally up-converted in the solar collector, boost the efficiency of the solar cell. The thermally up-converted component is enhanced by factor n2≈12 × , compared with the component that is lost to the environment, because it propagates in the internal optical modes of the semiconductor. (b) The structure of sample A used to demonstrate the efficiency enhancement due to thermal up-conversion. The device consists of a InGaAs/GaAsP quantum well solar cell (with absorption edge 1,000 nm) with a rear contact and electrical isolation layer of GaAs. Below the solar cell, electrically isolated InGaAs/GaAsP quantum wells (with absorption edge 1,060 nm) are located. This layer acts as a solar collector and emits thermally broadened PL to the solar cell.
