Hong-Yan Chen

Oxygen-deficient WO3−x@TiO2−x core–shell nanosheets for efficient photoelectrochemical oxidation of neutral water solutions

Preparation of highly active, stable and earth-abundant photoanodes for water oxidation is an important strategy to meet the demand of developing clean-energy technologies. In this paper, efficient and stable photoanodes based on oxygen-deficient black WO3−x@TiO2−x core–shell nanosheets with precisely controlled shell thickness have been fabricated for photoelectrochemical (PEC) conversion from neutral water solutions. The black WO3−x@TiO2−x core–shell nanosheet photoanode with the shell thickness of ∼15 nm achieved around 8 times higher photocurrent density (∼3.20 mA cm−2) than the pure WO3 photoanode at 1.23 V vs. the RHE. An improved onset potential with long-term PEC durability was also realized with the obtained black WO3−x@TiO2−x core–shell nanosheet photoanodes. The promoted PEC water oxidation performance was likely to be originated from enhanced light absorption, interfacial charge transfer and charge separation in these WO3−x@TiO2−x nanosheets which were revealed by finite-difference time-domain simulations and specific band alignment, along with optical and electrochemical spectroscopic evidence. In a word, such black WO3−x@TiO2−x nanosheet photoanodes suggest many exciting opportunities for PEC water splitting toward highly efficient solar fuel generation and many other PEC sensing applications.

Surface-plasmon mediated photoluminescence enhancement of Pt-coated ZnO nanowires by inserting an atomic-layer-deposited Al₂O₃ spacer layer.

Surface-plasmon mediated photoluminescence emission enhancement has been investigated for ZnO nanowire (NW)/Pt nanoparticle (NP) nanostructures by inserting an Al2O3 spacer layer. The thickness of the Al2O3 spacer layer and of the Pt NPs capped on the ZnO NWs are well controlled by atomic layer deposition. It is found that the photoluminescence property of the ZnO NW/Al2O3/Pt hybrid structure is highly tunable with respect to the thickness of the inserted Al2O3 spacer layer. The highest enhancement (∼14 times) of the near band emission of ZnO NWs is obtained with an optimized Al2O3 spacer layer thickness of 10 nm leading to a ultraviolet-visible emission ratio of 271.2 compared to 18.8 for bare ZnO NWs. The enhancement of emission is influenced by a Förster-type non-radiative energy transfer process of the exciton energy from ZnO NWs to Pt NPs as well as the coupling effect between excitons of ZnO NWs and surface plasmons of Pt NPs. The highly versatile and tunable photoluminescence properties of Pt-coated ZnO NWs achieved by introducing an Al2O3 spacer layer demonstrate their potential application in highly efficient optoelectronic devices.

Low temperature one-step growth of AlON thin films with homogenous nitrogen doping profile by plasma enhanced atomic layer deposition.

The AlON film with homogeneous nitrogen-doping profile was grown by plasma-enhanced atomic layer deposition (PEALD) at low temperature. In this work, the precursors of the NH3 and the O2 were simultaneously introduced into the chamber during the PEALD growth at a relatively low temperature of 185 °C. It is found that the composition of the obtained film quickly changes from AlN to Al2O3 when a small amount of O2 is added. Thus, the NH3:O2 ratio should be maintained at a relatively high level (>85%) for realizing the AlON growth. Benefited from the growth method, the nitrogen can be doped evenly in the entire film. Moreover, the AlON films exhibit a lower surface roughness than the AlN as well as the Al2O3 ones. The Al 2p and N 1s X-ray photoelectron spectra show that the AlON film is composed of Al-N, Al-O, and N-Al-O bonds. Moreover, a three-layer construction of the AlON film is proposed through the Si 2p spectra analysis and reconfirmed by the transmission electron microscopy characterization. At last, the electrical and optical tests indicate that the AlON films prepared in this work can be employed as the gate dielectric in transistor application as well as the antireflection layer in photovoltaic application.

Realizing a facile and environmental-friendly fabrication of high-performance multi-crystalline silicon solar cells by employing ZnO nanostructures and an Al2O3 passivation layer.

Nowadays, the multi-crystalline silicon (mc-Si) solar cells dominate the photovoltaic industry. However, the current acid etching method on mc-Si surface used by firms can hardly suppress the average reflectance value below 25% in the visible light spectrum. Meanwhile, the nitric acid and the hydrofluoric contained in the etching solution is both environmental unfriendly and highly toxic to human. Here, a mc-Si solar cell based on ZnO nanostructures and an Al2O3 spacer layer is demonstrated. The eco-friendly fabrication is realized by low temperature atomic layer deposition of Al2O3 layer as well as ZnO seed layer. Moreover, the ZnO nanostructures are prepared by nontoxic and low cost hydro-thermal growth process. Results show that the best passivation quality of the n+ -type mc-Si surface can be achieved by balancing the Si dangling bond saturation level and the negative charge concentration in the Al2O3 film. Moreover, the average reflectance on cell surface can be suppressed to 8.2% in 400–900 nm range by controlling the thickness of ZnO seed layer. With these two combined refinements, a maximum solar cell efficiency of 15.8% is obtained eventually. This work offer a facile way to realize the environmental friendly fabrication of high performance mc-Si solar cells.

An Investigation on a Crystalline-Silicon Solar Cell with Black Silicon Layer at the Rear

Crystalline-Si (c-Si) solar cell with black Si (b-Si) layer at the rear was studied in order to develop c-Si solar cell with sub-band gap photovoltaic response. The b-Si was made by chemical etching. The c-Si solar cell with b-Si at the rear was found to perform far better than that of similar structure but with no b-Si at the rear, with the efficiency being increased relatively by 27.7%. This finding was interesting as b-Si had a large specific surface area, which could cause high surface recombination and degradation of solar cell performance. A graded band gap was found to form at the rear of the c-Si solar cell with b-Si layer at the rear. This graded band gap tended to expel free electrons away from the rear, thus reducing the probability of electron-hole recombination at b-Si and improving the performance of c-Si solar cell.