When Te ≠ Th: investigating the operation of a two-temperature hot carrier solar cells

In hot carrier solar cells (HCSC), photo generated carriers are collected before they relax their excess of kinetic energy. Their increased temperature translates into a voltage boost, opening perspectives for high power conversion efficiency. These systems have been investigated assuming that electrons and holes share the same temperature; yet several processes tend to imbalance the two distributions and disturb the operation of the device. In this presentation, we report the first direct observation of a 2-temperatures (2T) hot carrier system. To do so, we perform a detailed analysis of the band filling signature on the photoluminescence signal of an InGaAsP QW sample. We then calculate analytically the influence of Te≠Th on the voltage of the cell, and adapt a detailed balance model to evaluate the operation of a 2T HCSC. We show that the temperature imbalance firstly impacts the fill factor of the device. This analysis also allows us to conclude that the key parameter to capture the performance of a HCSC is not Te or Th, but an effective temperature which is readily accessible through photoluminescence. This result illustrates the robustness of HCSC, which can theoretically maintain high efficiency of broad range of parameters.