Changchun Wei

Effective light trapping in thin film silicon solar cells from textured Al doped ZnO substrates with broad surface feature distributions

We used a multi-step process to make aluminum-doped ZnO (AZO) films with a wide range distribution of textures for light trapping in thin film silicon solar cells, which includes AZO deposition, HCl etching, AZO re-deposition, and HCl re-etching. The large features created by the first etching provide an effective light trapping for long wavelength light; the small features from the second etching enhances the short wavelength light trapping. Microcrystalline silicon solar cells deposited on the above-mentioned AZO show an improved photocurrent density without loss in the open-circuit voltage and fill factor, resulting in an overall increase in efficiency by 14.64%.

Half-metallicity and anisotropic magnetoresistance of epitaxial Co2FeSi Heusler films

In this paper, the anisotropic magnetoresistance (AMR) effect was investigated to check the half-metallic/non-half-metallic nature of epitaxial Co2FeSi films. The evolution of the microstructure shows that the B2 and L21-ordering of Co2FeSi films will increase with increasing annealing temperature which causes a decrease of the d-states in the down-spin channel. When Co2FeSi films are annealed at 650 °C, better B2 and L21-ordering will change the dominant s-d scattering from s↑→d↓ to s↑→d↑. The change from a non-half-metallic to a half-metallic nature of the Co2FeSi films induces a sign change of the AMR ratio from positive to negative and a small value of the Gilbert constant (α = 0.0022).

Elucidating the role of chlorine in perovskite solar cells

It has been proposed that introducing the chlorine anion into a CH3NH3PbI3 perovskite material can substantially improve the materials properties as well as the solar cell performance. To elucidate the role of chlorine in perovskite solar cells (PSCs), here we introduced PbCl2 into the precursor, and studied the chlorine configuration evolution during perovskite film formation and the associated influence on PSC performance in detail. We found that chlorine could be successfully incorporated into the precursor film in the form of PbICl or PbCl2 through a properly designed preparation, and it was conserved in the final perovskite film with a configuration of MAPbCl3, PbICl or PbCl2 depending on the fabrication process. However, no evidence of a MAPbI3−xClx phase was observed, and it is considered that MAPbI3−xClx might be metastable or possesses a higher formation energy. In addition, we demonstrate that the formation of a porous PbICl scaffold in the precursor film plays a key role in high quality perovskite film realization, benefiting from an effective stress release during structure expansion after methylammonium iodide dripping. Moreover, we propose that residual amorphous PbCl2 can effectively passivate defects in perovskite film, and dramatically improve the film’s electrical properties. Finally, n–i–p type planar PSCs with efficiencies up to 19.45% were achieved. It should be mentioned that the whole process for the formation of the PSCs is performed at less than 100 °C, which is beneficial for a wide range of applications, such as flexible and tandem solar cells.

High efficiency and high open-circuit voltage quadruple-junction silicon thin film solar cells for future electronic applications

Conversion of clean and renewable solar energy into electricity with photovoltaic (PV) devices, based on earth-abundant silicon elements to meet increasing global energy demands and environmental sustainability, has motivated various potential industrial and domestic applications. In addition to large-scale electricity production of market-dominant crystalline silicon PVs, the unique properties of silicon-based thin-film solar-cells (TFSCs) make them very attractive as affordable clean and safe energy devices. Herein, with large-scale and mature plasma-enhanced chemical vapor deposition (PECVD) process that can efficiently fabricate high-performing a-SiC:H, a-SiGe:H, a-Si:H, and μc-Si:H single- and various multi-junction TFSCs, we report a highly-efficient and flexibly tunable monolithic quadruple-junction silicon TFSC with a high photovoltage above 3.0 V and power conversion efficiency of 15.03% (NREL measured 14.58%). Our proposed high-voltage silicon TFSCs, with excellent performance, can further enrich the toolbox for functional photoelectrical devices and inspire possible future applications as highly promising power supply sources in charging electronics, splitting and disinfecting water, powering household electronic devices, solar to CO2 reduction, and other possible applications.

Role of hydrogen plasma pretreatment in improving passivation of the silicon surface for solar cells applications.

We have investigated the role of hydrogen plasma pretreatment in promoting silicon surface passivation, in particular examining its effects on modifying the microstructure of the subsequently deposited thin hydrogenated amorphous silicon (a-Si:H) passivation film. We demonstrate that pretreating the silicon surface with hydrogen plasma for 40 s improves the homogeneity and compactness of the a-Si:H film by enhancing precursor diffusion and thus increasing the minority carrier lifetime (τ(eff)). However, excessive pretreatment also increases the density of dangling bond defects on the surface due to etching effects of the hydrogen plasma. By varying the duration of hydrogen plasma pretreatment in fabricating silicon heterojunction solar cells based on textured substrates, we also demonstrate that, although the performance of the solar cells shows a similar tendency to that of the τ(eff) on polished wafers, the optimal duration is prolonged owing to the differences in the surface morphology of the substrates. These results suggest that the hydrogen plasma condition must be carefully regulated to achieve the optimal level of surface atomic hydrogen coverage and avoid the generation of defects on the silicon wafer.

Compound Homojunction:Heterojunction Reduces Bulk and Interface Recombination in ZnO Photoanodes for Water Splitting

Photoelectrochemical water splitting is far more efficient thanks to the novel ZnOSe/ZnO/BZO thin-film photoanodes fabricated in this work. A novel structure is developed for simultaneously suppressing the charge recombination in the ZnO bulk and at the semiconductor-electrolyte interface. This structure achieves a five-fold enhancement in water-splitting performance, compared to that of pristine ZnO photoanodes, when illuminated using visible light.

Hydrogenated TiO2 Thin Film for Accelerating Electron Transport in Highly Efficient Planar Perovskite Solar Cells

Abstract Intensive studies on low‐temperature deposited electron transport materials have been performed to improve the efficiency of n‐i‐p type planar perovskite solar cells to extend their application on plastic and multijunction device architectures. Here, a TiO2 film with enhanced conductivity and tailored band edge is prepared by magnetron sputtering at room temperature by hydrogen doping (HTO), which accelerates the electron extraction from perovskite photoabsorber and reduces charge transfer resistance, resulting in an improved short circuit current density and fill factor. The HTO film with upward shifted Fermi level guarantees a smaller loss on V OC and facilitates the growth of high‐quality absorber with much larger grains and more uniform size, leading to devices with negligible hysteresis. In comparison with the pristine TiO2 prepared without hydrogen doping, the HTO‐based device exhibits a substantial performance enhancement leading to an efficiency of 19.30% and more stabilized photovoltaic performance maintaining 93% of its initial value after 300 min continuous illumination in the glove box. These properties permit the room‐temperature magnetron sputtered HTO film as a promising electron transport material for flexible and tandem perovskite solar cell in the future.

Molybdenum-supported amorphous MoS3 catalyst for efficient hydrogen evolution in solar-water-splitting devices

We report molybdenum (Mo) metal-supported amorphous molybdenum sulfide (a-MoS3) catalysts with a porous and nanostructure nature, which exhibit excellent catalytic activity for the hydrogen evolution reaction (HER) in wired solar-water-splitting devices. Mo-supported a-MoS3 catalysts were prepared by wet chemically synthesizing a-MoS3 nanoparticles at room-temperature and then loading with Earth-abundant and scalable Mo metals sputtered at low temperature (100 °C). Electrochemical studies and applications in wired photoelectrochemical/photovoltaic (PEC–PV) solar-water-splitting devices reveal that the HER performance of wired PEC–PV solar-water-splitting devices can be efficiently enhanced with the proposed highly conductive Mo-supported a-MoS3 catalysts by enlarging the electrochemically active areas, accelerating the electron transport to active sites, and improving the charge transfer at the catalysts/electrolyte interfaces. The low-temperature preparation of highly active Mo-supported a-MoS3 catalysts paves the way to integrating them into various high-performance PV devices to develop highly efficient, scalable, low-cost, and monolithic PEC–PV solar-water-splitting devices.

Highly wettable and metallic NiFe-phosphate/phosphide catalyst synthesized by plasma for highly efficient oxygen evolution reaction

Many catalysts exhibit a high overpotential with a current density of 10 mA cm−2 for the oxygen evolution reaction (OER). High conductivity, wettability and active sites play key roles for a highly efficient OER catalyst. Here, we report a NiFe foam starting material treated with a two-step process using plasma-enhanced chemical vapor deposition (PECVD) in the presence of PH3, CO2 and H2, to form phosphate (Pi) and phosphide (P) groups on the foam, and forming NiFePi/P. The self-supported material combines conductivity, wettability with active sites, and is used directly as a working electrode for excellent oxygen evolution in alkaline solutions. Significantly, the strong synergistic effect between the phosphate and phosphide lead to a change in the surrounding electronic environment of metal ions that contributes to the increase in active sites, while improving the wettability and metallic nature of the catalyst, both of these result in an enhanced OER performance. This new material and design strategy appear to represent an intriguing advance that is likely to be of considerable interest to other researchers in the field.

Band alignment and enhancement of the interface properties for heterojunction solar cells by employing amorphous–nanocrystalline hierarchical emitter layers

Excellent electrical and passivation properties of p-type emitter layers are extremely important for high efficiency silicon heterojunction (SHJ) solar cells. The emitter layer should be embedded between the transparent conductive oxide (TCO) and the intrinsic amorphous silicon passivation layer, and thus the contact characteristics of p/TCO should also be carefully regulated to achieve better performance. Multifunctional p-type emitter layers combined with hydrogenated amorphous silicon/nanocrystalline silicon thin films were fabricated by the plasma enhanced chemical vapor deposition process, to meet the requirements of high conductivity and shortening of the depletion region between the p layer and TCO. Also, the p-a-Si:H film of the hybrid structure can serve as a buffer-layer to compensate the p/i band offset and a protective-layer for the intrinsic passivation films. Finally, applying this hybrid film as an emitter layer for SHJ solar cells based on low-cost commercial Cz silicon wafers, a conversion efficiency improvement of 2.6% in the solar cell photovoltaic performance has been achieved.