Zhongwei Yu

Ultrafast Solar‐Blind Ultraviolet Detection by Inorganic Perovskite CsPbX3 Quantum Dots Radial Junction Architecture

Inorganic CsPbX3 (X = Cl, Br, I, or hybrid among them) perovskite quantum dots (IPQDs) are promising building blocks for exploring high performance optoelectronic applications. In this work, the authors report a new hybrid structure that marries CsPbX3 IPQDs to silicon nanowires (SiNWs) radial junction structures to achieve ultrafast and highly sensitive ultraviolet (UV) detection in solar-blind spectrum. A compact and uniform deployment of CsPbX3 IPQDs upon the sidewall of low-reflective 3D radial junctions enables a strong light field excitation and efficient down-conversion of the ultraviolet incidences, which are directly tailored into emission bands optimized for a rapid photodetection in surrounding ultrathin radial p-i-n junctions. A fast solar-blind UV detection has been demonstrated in this hybrid IPQD-NW detectors, with rise/fall response time scales of 0.48/1.03 ms and a high responsivity of 54 mA W-1 @200 nm (or 32 mA W-1 @270 nm), without the need of any external power supply. These results pave the way toward large area manufacturing of high performance Si-based perovskite UV detectors in a scalable and low-cost procedure.

Rapid cooling and magnetic field-induced cooperative effect for the metastable quintet state in a spin crossover complex

Our study shows that metastable quintet state of spin crossover complex [Fe(dpp)2(NCS)2]⋅py (dpp=dipyrido[3,2-a:2′,3′-c] phenazine, py=pyridine) at low temperatures may be realized by a rapid cooling. The relaxation from quintet state to singlet spin at low temperatures depends on the both of time and previous history of the sample. The U-shaped dents of the magnetic effective moment depending on the temperature after initial rapid zero-field cooling indicate an obvious affection of magnetic field to the realization of singlet state in the transition range. The observations for this sample are indeed consistent with the fact that cooperative effects play a very important role in the spin transition.

The larger polar Kerr rotation of Fe-Si alloy films and their magnetic properties

The structure, magnetic properties and polar Kerr effects of Fe100−xSix (0⩽x⩽70) alloy films prepared by ion-beam co-sputtering were studied. We find that the saturation magnetization of these films decreases with increasing x, and a plateau of constant magnetization occurs as 22⩽x⩽28. Their polar Kerr rotation θk decreases with increasing x as x⩽16.2 and x⩾30, but increases with increasing x as 20⩽x⩽28. In the measuring wavelength range of 400–800 nm, the θk of Fe72Si28 film is 40% to 50% larger than that of pure Fe film. We think that amorphization may play an important role in enlarging the polar Kerr rotation of these films.

Full potential of radial junction Si thin film solar cells with advanced junction materials and design

Combining advanced materials and junction design in nanowire-based thin film solar cells requires a different thinking of the optimization strategy, which is critical to fulfill the potential of nano-structured photovoltaics. Based on a comprehensive knowledge of the junction materials involved in the multilayer stack, we demonstrate here, in both experimental and theoretical manners, the potential of hydrogenated amorphous Si (a-Si:H) thin film solar cells in a radial junction (RJ) configuration. Resting upon a solid experimental basis, we also assess a more advanced tandem RJ structure with radially stacking a-Si:H/nanocrystalline Si (nc-Si:H) PIN junctions, and show that a balanced photo-current generation with a short circuit current density of Jsc = 14.2 mA/cm2 can be achieved in a tandem RJ cell, while reducing the expensive nc-Si:H absorber thickness from 1–3  μ m (in planar tandem cells) to only 120 nm. These results provide a clearly charted route towards a high performance Si thin film photovolt...

Bi-Sn alloy catalyst for simultaneous morphology and doping control of silicon nanowires in radial junction solar cells

Low-melting point metals such as bismuth (Bi) and tin (Sn) are ideal choices for mediating a low temperature growth of silicon nanowires (SiNWs) for radial junction thin film solar cells. The incorporation of Bi catalyst atoms leads to sufficient n-type doping in the SiNWs core that exempts the use of hazardous dopant gases, while an easy morphology control with pure Bi catalyst has never been demonstrated so far. We here propose a Bi-Sn alloy catalyst strategy to achieve both a beneficial catalyst-doping and an ideal SiNW morphology control. In addition to a potential of further growth temperature reduction, we show that the alloy catalyst can remain quite stable during a vapor-liquid-solid growth, while providing still sufficient n-type catalyst-doping to the SiNWs. Radial junction solar cells constructed over the alloy-catalyzed SiNWs have demonstrated a strongly enhanced photocurrent generation, thanks to optimized nanowire morphology, and largely improved performance compared to the reference samples based on the pure Bi or Sn-catalyzed SiNWs.

Boosting light emission from Si-based thin film over Si and SiO(2) nanowires architecture.

Silicon (Si)-based light emitting thin film has been a key ingredient for all-Si-based optoelectronics. Besides material engineering, adopting a novel 3D photonic architecture represents an effective strategy to boost light excitation and extraction from Si-based thin film material. We here explore the use of a nanowires (NW) framework, grown via vapor-liquid-solid mode, to achieve strongly enhanced yellow-green luminescence from SiN(x)O(y)/NW core-shell structure, with an order of magnitude enhancement compared to co-deposited planar references. We found that choosing geometrically-identical but different NW cores (Si or SiO(2)) can lead to profound influence on the overall light emission performance. Combining parametric investigation and theoretical modeling, we have been able to evaluate the key contributions arising from different mechanisms that include near-field enhancement, 3D light trapping and enhanced light extraction. These new findings indicate a new and effective strategy for strong Si-based thin film light emitting source, while being generic enough to be applicable in a wide variety of other thin film materials.