Intermediate‐band effect in hot‐carrier solar cells

Abstract

AbstractI have proposed that two‐step photoexcitation of carriers is feasible in hot‐carrier solar cells (HC‐SCs), like that in intermediate‐band solar cells (IB‐SCs). The second excitation from the IB to the conduction band (CB) in an IB‐SC is regarded to make the carriers in the unoccupied band hot. In an analogous way, in an HC‐SC, a photoexcited carrier arising from the interband transition can be further excited by the next photon via the intraband transition. In other words, the lower‐energy states in the CB function as the IB. Owing to this IB effect, the absorbed energy increases while the excited carrier number decreases under the optimal operating conditions; the latter leads to a decrease in the energy dissipation associated with the hot‐carrier extraction. Consequently, the limiting conversion efficiency of the HC‐SCs improves by up to 6% to 9% (absolute) compared with that with no IB effect, under the condition of the carrier thermalization time of 1 ns and 1000 times concentrated solar illumination. The detrimental impact of the increase in the emitted energy due to the intraband transition is well suppressed under the suitable operating conditions. Thus, the IB effect always provides positive results even if the effect is weak, contrasting to that the weak second excitation could lower the conversion efficiency of an IB‐SC.