[20a-B12-1~8] 13.9 Compound solar cells

[20a-B12-3] Synergy effect of intraband transition and impact ionization in optical hot-carrier solar cells

〇Yasuhiko Takeda¹ (1.Toyota Central R&D Labs.)

Keywords:hot-carrier solar cells, impact ionization, hot luminescence

I have revealed the means to further improve conversion efficiency of optical hot-carrier solar cells (opt-HC-SCs) using an improved detailed balance model. The enhancement effect of the optical energy-selective contact on the hot luminescence is substantially lower in practice than the optimal value, which requires a high carrier density in the absorber for sufficient photon extraction, and consequently energy loss originating from carrier thermalization is significant. When impact ionization occurs immediately, the average carrier energy lowers, the carrier density can decrease, and hence the thermalization energy loss reduces remarkably. This, in turn, enables absorption of sub-bandgap photons arising from intraband transition to improve the efficiency. Thus, the synergy effect of these two phenomena notably improves the efficiency from 45.1% to 53.6%, although the individual effects are marginal. This is a unique feature of opt-HC-SCs and not found in HC-SCs (carrier extraction).