Effects of impact ionization and Auger recombination on hot-carrier solar cells and hot-carrier photocatalysts

We applied hot-carrier extraction to solar cells and photocatalysts used for artificial photosynthesis including water splitting and CO2 reduction, and elucidated the differences between these two applications: hot-carrier solar cells (HC-SCs) and hot-carrier photocatalysts (HC-PCs) by detailed balance calculations. The hot-carrier effect in the photocatalysts is less significant than that in the solar cells, because of the larger bandgaps required for generating sufficiently high-energy carriers consumed for the reactions. On the other hand, impact ionization and Auger recombination (IA) improves the efficiency of the HC-PCs more notably, because the IA functions like photon upconverters and hence narrows the optimal bandgap. Furthermore, the IA improves the spectral robustness by eliminating the constraint of the particle-number conservation for both the HC-SCs and HC-PCs. These benefits of the IA are contrasting with the well-recognized fact that the IA only reduces the carrier number and consequently lowers the efficiency of the conventional counterparts.