Controlled Synthesis of Vertically Aligned SnO₂ Nanograss-Structured Thin Films for SnO₂/BiVO₄ Core–Shell Heterostructures with Highly Enhanced Photoelectrochemical Properties

Abstract

Fabrication of semiconductor thin films with uniform and vertically aligned one-dimensional nanostructures is an active area of research. We report the synthesis of vertically aligned nanograss (NG)-structured SnO2 thin films on a wide range of substrates with a vapor–solid deposition process. In this process, some chemical and physical parameters, such as chemical composition, deposition height from the precursor mixture, deposition temperature, and substrate roughness, are found to play key roles during the growth of SnO2 nanograsses (SNGs). The effects of density change and cross-sectional dimension (width) of the nanograsses (NGs) on surface area improvement of the thin films have been examined by varying the respective parameters. BiVO4 (BV) solution layers were coated onto SNG, forming core–shell type-II heterojunction thin films (SNG-BV). The thickness of the drop-cast BiVO4 solution layers onto the NGs was controlled by the number density of the NGs per unit area. Light absorption efficiency (ηabs) of the core–shell SNG-BV films has been optimized by controlling quasi-arranged periodicity of the core NGs and accessible shell thickness of BiVO4 layers. The charge separation efficiency (ηsep) of SNG-BV films strongly depends on the thickness of the BiVO4 layers onto NGs. Thin layers of BiVO4 coating along the axial direction of thinner SnO2 NGs (25–50 nm) shows enhanced ηsep but lower ηabs due to poor light absorption. On the other hand, the thicker core NGs (40–200 nm) with low surface area provide thick layers of BiVO4, which drives strong light absorption but suffers from efficient ηsep. However, intermediate layers of BiVO4 onto uniformly arranged SnO2 NGs with 30–70 nm width shows enhanced ηabs as well as efficient ηsep compared to other SNG-BV samples. This result demonstrates that control over the horizontal dimension of the core materials in the core–shell heterojunction (keeping vertical restriction) is a viable approach for optimizing the photoelectrochemical efficiency.

Controlled Growth of CdS Nanostep Structured Arrays to Improve Photoelectrochemical Performance

“…Upon further increasing the reaction time to 3 h, an obvious nanostep structure was formed on the surface of the CdS rods. The nanostep structure may be beneficial for enhancing the light absorption due to the multi-scattering and reflection effect of light (Bera et al, 2018 ). However, the nanostep structure disappeared as the time was extended to 4 h. In this case, the CdS rod was transformed into a thinner and irregular rod ( Figure 2D ), only ~100 nm in diameter, in contrast with the nanostep structural rod with a ~600 nm in diameter.…”

Indium Oxide Based Nanomaterials: Fabrication Strategies, Properties, Applications, Challenges and Future Prospect

“…It is worthy to note that overall PEC performance for solar water splitting depends on three fundamental factors-(i) absorption efficiency (ƞ abs ), (ii) charge separation efficiency (ƞ sep ) and (iii) charge transfer efficiency (ƞ trans ). The performance for solar water splitting is expressed as ƞ abs × ƞ sep × ƞ trans [53]. It is very challenging to get high value of the product of ƞ abs and ƞ sep (i.e.…”

“…It is very challenging to get high value of the product of ƞ abs and ƞ sep (i.e. ƞ abs × ƞ sep ) because these are coupled with each other [53]. By increasing the active layer thickness, it is possible to increase ƞ abs value but it reduces the ƞ sep value.…”

“…However, the nanostructuring on MOS metal oxide thin film surfaces can mitigate the problem. Several nanostructured mixed metal oxide thin films including IO based nanostructured thin films are reported for improving PEC performances [4,6,53].…”

Rational Design of 3D Hierarchical Ternary SnO2/TiO2/BiVO4 Arrays Photoanode toward Efficient Photoelectrochemical Performance

“…Besides, the host–guest heterojunction electrode using two or more dissimilar materials to take the task of charge transport and light absorption, respectively, is another popular strategy to promote the charge transport and suppress the recombination of electron–hole pairs . For instance, BiVO 4 as a light absorber has been combined with various other semiconductors to form a type II configuration such as TiO 2 /BiVO 4 , WO 3 /BiVO 4 , SnO 2 /BiVO 4 , and Fe 2 O 3 /BiVO 4 . Among them, TiO 2 is very attractive due to its relatively negative flat band potential and good chemical stability.…”