(Invited) Stabilizing Semiconductor-Solution Interfaces Via Chemically Stable but Electronically Defective Coatings
The n-doped Si/TiO2/Ni structure also operates as a high barrier height junction for solar energy conversion. To further understand the mechanism of “leaky” TiO2 protection and the role of Ni electrocatalyst overlayers, we used Si/TiO2/Ni structures as a model system to study solid-solution interfaces. TiO2 coatings of 3 – 143 nm in thickness introduce two interfaces: a TiO2/liquid interface and a TiO2/n-Si heterojunction. We have employed operando ambient-pressure X-Ray photoelectron spectroscopy (AP-XPS) to study TiO2/Ni/liquid and TiO2/liquid interfaces, and directly observed their ohmic and rectifying junction behavior, respectively. We also extensively investigated n-Si/TiO2 heterojunction interfaces by employing photoelectrochemical, solid-state electrical, and photoelectron spectroscopic techniques. The distinctive electrical behavior of n-Si/TiO2 heterojunctions will be compared with conventional semiconductor/metal and semiconductor/liquid junctions. Because electronic defect states exist in band gaps of “leaky” TiO2, their effects on the formation of n-Si/“leaky”TiO2 heterojunctions will be discussed. This interfacial study reveal several strategies for improving the performance of thin-layer protected photoelectrodes as well as for further expanding selection of “leaky” protective coatings.