Exploring the Effects of Crystal Facet Orientation at the Heterojunction Interface on Charge Separation for Photoanodes

As one of the most effective strategies to promote the spatial separation of charges, constructing heterojunction has received extensive attention in recent years. However, it remains unclear whether the crystal facet orientation (CFO) at the heterojunction interface is contributory to charge separation. Herein, three types of TiO2/CdS heterojunction films with different CFOs at the heterojunction interface were produced by adjusting the CdS CFO through in situ conversion. Among them, the TiO2/CdS film with a mixed CdS CFO showed the maximum photocurrent density and charge separation efficiency. In contrast, the TiO2/CdS film with a uniform CdS (100) (CdS100) performed worst. According to the results of experimentation and DFT calculation, these three types of TiO2/CdS films varied significantly in electron transport time. This is attributable to the different Fermi levels of CdS CFO and the formation of different built-in electric fields upon coupling with TiO2. The rise in the Fermi level of CdS can increase the driving force required for charge migration at the heterojunction interface. Additionally, a stronger built-in electric field is conducive to charge separation. To sum up, these results highlight the significant impact of CFO at the heterojunction interface on charge separation.

Automated summary

Constructing heterojunction is an effective strategy to promote charge separation, but the contribution of crystal facet orientation (CFO) at the heterojunction interface remains unclear. In this study, by adjusting the CdS CFO, three types of TiO2/CdS heterojunction films with different CFOs were produced. The TiO2/CdS film with a mixed CdS CFO showed the highest photocurrent density and charge separation efficiency, while the film with a uniform CdS (100) performed the worst. The different electron transport times of these films are attributed to the varying Fermi levels of CdS CFO and the formation of different built-in electric fields when coupled with TiO2.