The effect of the effective electron mass on the hot electron collection

Abstract

The dominant factor for hot electron collecting in internally photoemitted hot carrier (IPHC) devices is still not clear under steady-state low intensity light. We here use SnO2 as the electron-collecting layer to replace TiO2 to construct IPHC devices. Almost no photoresponse is observed for the pure SnO2-based IPHC device. However, when an insulating MgO layer or TiO2 covered SnO2, relatively large photocurrent generated from hot electrons can be achieved. The effective electron mass (EEM) is figured out to be the dominate factor in hot electron collection in IPHC devices. The very small EEM of SnO2 results in a small emission cone of hot electrons. Also due to the small EEM of SnO2, the leakage of trapped electrons back to the Au is very large. Because of these two reasons, the SnO2-based IPHC device shows almost no photoresponse. MgO can block the backflow of electrons (leakage), while the larger EEM of TiO2 can increase the emission cone of hot electrons. Our finding is significant for understanding hot electrons collection and will give new directions for hot carrier solar cell applications under low-intensity excitation at steady state.