Enabling Efficient Charge Separation for Optoelectronic Conversion via an Energy-Dependent Z-Scheme n-Semiconductor–Metal–p-Semiconductor Schottky Heterojunction

Abstract

Achieving good charge separation while maintaining energetic electronic states in heterostructures is a challenge in designing efficient photocatalyst materials. Using first-principles calculations, we propose a Z-scheme Sn–m–Sp (n-semiconductor–metal–p-semiconductor) heterojunction as a viable avenue for achieving broad-spectrum sunlight absorption and, importantly, energy-dependent charge separation. As a proof-of-concept investigation, we investigated two ternary heterostructures, CdS–Au–PdO and SnO2–W–Ag2O, in which the electronic Fermi levels line up by virtue of the presence of an intermediate metal layer. A cascade of work functions in the relative order W n < W m < W p drives electrons flowing from Sn to m and from m to Sp. The inner electric fields established at the Sn–m and m–Sp Schottky junctions selectively guide low-energy photoexcited electrons from Sn (CdS/SnO2) and low-energy holes from Sp (PdO/Ag2O) to the interposing Au or W metal, respectively. Importantly, relatively low Schottky barriers enforce charge separation by constraining high-energy photogenerated charges to the individual semiconductor layers. Operating together, these two mechanisms enable the achievement of highly efficient optoelectronic conversion.

Synergistic Effect of Work Function and Acoustic Impedance Mismatch for Improved Thermoelectric Performance in GeTe-WC Composite

“…It is noted that for the semiconductor (Ge 0.87 Mn 0.05 Sb 0.08 Te)−metal (WC) junction, there can be either Schottky contact (work function φ of the metal is greater than that of the semiconductor) or Ohmic contact (work function of the semiconductor is greater than that of metal). 51,52 The present study shows that the work function for WC is smaller than that of Ge 0.87 Mn 0.05 Sb 0.08 Te, indicating an Ohmic contact and hence further supports the linear nature of the I−V curve in Figure 4c. It indicates that charge carriers can flow from WC to Ge 0.87 Mn 0.05 Sb 0.08 Te, supporting the enhanced σ in the system.…”

Direct Z-Scheme Photocatalytic System: Insights into the Formative Factors of Photogenerated Carriers Transfer Channel from Ultrafast Dynamics

“…Photocatalysis technology has been considered as an attractive approach to overcome serious energy and environmental crises by utilizing inexhaustible solar energy to drive various chemical reactions, such as overall water splitting, carbon dioxide reduction, and various contaminations degradation. − Compared with single-component photocatalysts, the conventional type II heterojunction photocatalysts, consisting of two different semiconductors with the staggered band structure alignment, can efficiently improve the spatial separation of photogenerated electrons and holes (PEHs) to suppress the recombination of photogenerated carriers. − Unfortunately, the efficient separation of PEHs is at the expense of the redox ability of the photogenerated carriers. − Inspired by the natural photosynthesis of plants, the artificial Z-scheme heterojunction system not only boosts the separation of PEHs, but also preserves their strong redox properties, which can obviously enhance the photocatalytic performance. − …”

Inside‐and‐Out Semiconductor Engineering for CO2 Photoreduction: From Recent Advances to New Trends

“…Interestingly, it was highlighted that the integration of plasmonic effect and Schottky junctions has the potential to enhance visible‐light harvesting and photoinduced charge carries separation for high photocatalytic activity. [ 352–355 ] For example, copper with plasmonic effect was encapsulated in UiO‐66 to form Schottky junctions (Cu/Cu@UiO‐66). [ 356 ] The photocatalytic performance of Cu/Cu@UiO‐66 was enhanced by encapsulating a very low concentration of Cu, which attributed to a synergy of plasmonic effect and Schottky junctions to allow the visible‐light absorption and electron capture.…”