Peizhi Yang

Photoelectric conversion beyond sunny days: all-weather carbon quantum dot solar cells

Since the birth of solar cells, photovoltaic devices have experienced persistent breakthroughs in either crucial materials or technologies. However, the ability for power generation is only limited under sunlight illumination, i.e., all state-of-the-art solar cells can realize high-efficiency electricity outputs on sunny days. The power conversion efficiencies are zero at nights because of relatively low visible-light intensity. We present here a simple hydrothermal conversion from strawberry powders to carbon quantum dots (CQDs) for all-weather solar cell applications. Using green-emitting long persistence phosphors (LPPs) as light placeholders, the unabsorbed light ranging from visible to infrared light across CQD sensitized mesoscopic titanium dioxide (m-TiO2) can be converted into green fluorescence, allowing for persistent CQD irradiation and therefore electricity generation at nights.

Characterization of PECVD grown porous SiO2 thin films with potential application in an uncooled infrared detector

Plasma-enhanced chemical vapor deposition (PECVD) technology was considered as an excellent thin film deposition dry process in semiconductor device fabrication. Porous SiO2 film as a promising thermal insulation layer used in uncooled infrared detectors was grown directly by PECVD technology. The microstructure and elemental composition of the film were characterized by AFM, EDS, SEM and XPS. The porosity of the film was assessed according to the refractive index measured by ellipsometery. A prototype pyroelectric uncooled detector coated with a porous SiO2 film was evaluated.

Size-controlled Si quantum dots embedded in B-doped SiNx/Si3N4 superlatice for Si quantum dot solar cells

Under the condition of the fixed Si3N4 layer thickness of 1.1 nm, Si-QDs embedded in B-doped SiNx/Si3N4 multilayer thin films with various SiNx layer thickness were fabricated respectively. Si-QDs with controllable and nearly uniform size were formed in SiNx layers, and found that the optical band gap of the films can be adjusted by changing the thickness of SiNx layer. On the basis of this, the Si-QDs/c-Si heterojunction solar cells were prepared. It is found that the larger the band gap is, the higher the cell efficiency is. The best performance device is obtained with average QD size of ~3.5 nm, which has the highest efficiency of 7.05 % compared with the other two devices. This difference is caused by the difference of the spectral response of these devices.

Preparation of a MoS2/carbon nanotube composite as an electrode material for high-performance supercapacitors

MoS2 and MoS2/carbon allotrope (MoS2/C) composites for use as anodes in supercapacitors were prepared via a facile hydrothermal method. In this study, we report the effects of various carbon-based materials (2D graphene nanosheet (GNS), 1D carbon nanotube (CNT), and 0D nano carbon (NC)) on the electrochemical performances. Among all nanocomposites studied, MoS2/CNT exhibited the best electrochemical performance. Specifically, the MoS2/CNT composite exhibits remarkable performances with a high specific capacitance of 402 F g−1 at a current density of 1 A g−1 and an outstanding cycling stability with 81.9% capacitance retention after 10 000 continuous charge–discharge cycles at a high current density of 1 A g−1, making it adaptive for high-performance supercapacitors. The superiority of MoS2/CNT was investigated by field emission scanning electron microscopy and transmission electron microscopy, which showed that MoS2 nanosheets were uniformly loaded into the three-dimensional interconnected network of nanotubes, providing an excellent three dimensional charge transfer network and electrolyte diffusion channels while effectively buffering the collapse and aggregation of active materials during charge–discharge processes. Overall, the MoS2/CNT nanocomposite synthesized by a simple hydrothermal process presents a new and promising candidate for high-performance anodes for supercapacitors.

A double-layered photoanode made of ZnO/TiO2 composite nanoflowers and TiO2 nanorods for high efficiency dye-sensitized solar cells

We present a simple sol-gel hydrothermal process for the fabrication of a double-layered structure composed of a TiO2 nanorod overlayer and TiO2 nanoparticle-embedded ZnO nanoflower (ZNFs@TNPs-TNRs) underlayer. The ZNFs@TNPs-TNRs was used as a photoanode in dye-sensitized solar cells (DSSCs) and their photovoltaic performance was analyzed. The ZNFs@TNPs-TNRs can enhance the adsorption of N719 dyes, charge transport, and light scattering. The cell performances can be maximized by optimizing thickness ratio and total thickness of the double-layered photoanode, and the preliminary results demonstrate that a promising power conversion efficiency (PCE) of 8.01% is determined on the DSSC with ZNFs@TNPs-TNRs anode, yielding a 28.9% enhancement in the PCE in comparison to pristine TiO2–P25 nanoparticle-based DSSC.

Microwave annealing enhances formation of silicon quantum dots in oxide matrix

In this work, an effective strategy for the controlled synthesis of Si-QDs embedded Si-rich silicon oxide/SiO2 (SRO/SiO2) multilayers using susceptor-assisted microwave annealing (MWA) is introduced. Both MWA and rapid thermal annealing (RTA) were compared to study the growth of Si-QDs embedded in SRO/SiO2 multilayers, and found that the temperature required for forming Si-QDs decreases by 200 °C under MWA. SRO single-layer films were used for the investigation of growth mechanism during MWA. It is shown that MWA annealing could enhance the phase separation in SRO films and more Si-QDs precipitated in SRO film annealed by MWA than RTA one. These results demonstrate that the microwave electromagnetic field has unique influence on the generated Si-QDs, can be considered as an archetype of a non-thermal microwave effect.