Electrical, Photoelectrochemical, and Photoelectron Spectroscopic Investigation of the Interfacial Transport and Energetics of Amorphous TiO₂/Si Heterojunctions

Abstract

Solid-state electrical, photoelectrochemical, and photoelectron spectroscopic techniques have been used to characterize the behavior and electronic structure of interfaces between n-Si, n + -Si, or p + -Si surfaces and amorphous coatings of TiO 2 formed using atomiclayer deposition. Photoelectrochemical measurements of n-Si/TiO 2 /Ni interfaces in contact with a series of one-electron, electrochemically reversible redox systems indicated that the n-Si/TiO 2 /Ni structure acted as a buried junction whose photovoltage was independent of the formal potential of the contacting electrolyte. Solid-state current−voltage analysis indicated that the built-in voltage of the n-Si/TiO 2 heterojunction was ∼0.7 V, with an effective Richardson constant ∼1/100th of the value of typical Si/metal Schottky barriers. X-ray photoelectron spectroscopic data allowed formulation of energy band-diagrams for the n-Si/ TiO 2 , n + -Si/TiO 2 , and p + -Si/TiO 2 interfaces. The XPS data were consistent with the rectifying behavior observed for amorphous TiO 2 interfaces with n-Si and n + -Si surfaces and with an ohmic contact at the interface between amorphous TiO 2 and p + -Si.

Combined soft and hard X-ray ambient pressure photoelectron spectroscopy studies of semiconductor/electrolyte interfaces

“…As a result, PES has been successfully used to correlate semiconductor band edge positions and band bending with the chemical composition of their surfaces [19,20]. Such an approach has been recently used to study band alignment at the solid-solid interface formed between silicon and TiO 2 protection layers for photoelectrochemical applications [21]. A standard experimental procedure for conducting these studies is to vacuum deposit a solid overlayer, layer-by-layer onto the substrate while simultaneously monitoring both valence and core-level spectra [22].…”

Metal–Organic Framework Derived Co3O4/TiO2/Si Heterostructured Nanorod Array Photoanodes for Efficient Photoelectrochemical Water Oxidation

“…[8][9][10] Therefore, to achieve effective solar-to-hydrogen (STH) process, all steps stated above should be in very efficient progress, which requires high optical response for the photoanode materials, [11] efficient carrier separation, and surface reaction. [26] As the conduction band (CB) of silicon is more negative than most of the common MO semiconductors (e.g., TiO 2 , [27,28] WO 3 ), [29] silicon can bring better electron reduction kinetics on the counter electrode. However, as intrinsic semiconductor, the PEC performance of pristine MO photoanode is always hindered by the poor carrier mobility, narrow optical-response range, and slow surface water oxidation kinetics.…”

“…[26] As the conduction band (CB) of silicon is more negative than most of the common MO semiconductors (e.g., TiO 2 , [27,28] WO 3 ), [29] silicon can bring better electron reduction kinetics on the counter electrode. Particularly, benefiting from the outstanding visiblelight response performance and carrier mobility within silicon, it has long been regarded as the most suitable material to build the solar energy conversion device.…”

“…However, as intrinsic semiconductor, the PEC performance of pristine MO photoanode is always hindered by the poor carrier mobility, narrow optical-response range, and slow surface water oxidation kinetics. [26] As the conduction band (CB) of silicon is more negative than most of the common MO semiconductors (e.g., TiO 2 , [27,28] WO 3 ), [29] silicon can bring better electron reduction kinetics on the counter electrode. [20][21][22] For instance, via constructing semiconductor heterojunction with matched band position, the separation and transportation of photoinduced carrier can be effectively enhanced (such as Bi 2 MoO 6 /Si, [23] Ag/Fe 2 O 3 , [24] NiFe-LDH/C 3 N 4 [25] heterojunction).…”

TiO2 Films from the Low‐Temperature Oxidation of Ti as Passivating‐Contact Layers for Si Heterojunction Solar Cells

“…Among the electron‐selective transport materials mentioned above, TiO 2 is one of the few materials that can spontaneously satisfy the dual functions of interfacial passivation and carrier‐selective transport. Many fabrication technologies have been developed to deposit high‐quality TiO 2 layers, such as chemical vapor deposition (CVD), atomic layer deposition (ALD), evaporation, and sol–gel processes . Benefiting from chemical and field‐effect passivation, the ALD/CVD‐deposited TiO 2 layers can effectively passivate a Si surface with a surface recombination velocity down to 10 cm s −1 .…”