Enhancing the Carrier Transport in Dielectric Passivation Layers via the Introduction of Trap States toward Improved CH3NH3PbI3/Si Heterojunction Photodetectors

Dielectric thin layers have commonly been employed to passivate interfacial defects to improve the performance of heterojunction photodetectors (PDs), whereas their insulating nature severely hinders the out-of-plane carrier transport, thereby limiting the improvements in performance. Fortunately, such a problem can be well addressed by modulating the charge carriers' transport process by introducing trap states. Herein, we reported the fabrication of much-improved CH₃NH₃PbI₃/Si heterojunction PDs achieved by employing a HfO_2+x thin film with high-density (OH)_O (i.e., OH substitute for O lattice site) as the interfacial passivation layer. Theoretical studies suggested that (OH)_O defects have a low formation energy and exhibit hole-trapping behaviors. Notably, the interfacial passivation effects of the HfO_2+x thin films are comparable to those of the HfO₂ thin films. In addition, the out-of-plane hole transport was enhanced in the HfO_2+x thin films benefiting from the efficient (OH)_O trap-assisted transport of holes. Finally, the performance of HfO_2+x-passivated PDs was remarkably improved. It is believed that the results demonstrated in this work provide a promising strategy for the fabrication of efficient heterojunction PDs in the future.