Highly efficient solar cells using hot carriers generated by two-step excitation

We propose a novel type of highly efficient solar cells: intermediate-band-assisted hot-carrier solar cells (IB-HC-SCs). Carriers are generated by two-step photo-excitation via intermediate bands, and extracted through energy-selective contacts before they are completely thermalized. The two-step excitation dramatically reduces entropy generation associated with hot-carrier extraction. As a result, limiting conversion efficiency is significantly improved to be around 60% (0.1 sun)–70% (1000 sun), even though considering a finite thermalization time of hot carriers being 1 ns. This improvement is contrasting to the fact that the limiting conversion efficiency of usual hot-carrier cells under 1 sun irradiation is higher only slightly than the Shockley–Queisser limit (34%), because of the remarkable entropy generation.