Jindan Zhang

Photoinduced Silver Nanoparticles/Nanorings on Plasmid DNA Scaffolds

Biological scaffolds are being actively explored for the synthesis of nanomaterials with novel structures and unexpected properties. Toroidal plasmid DNA separated from the Bacillus host is applied as a sacrificial mold for the synthesis of silver nanoparticles and nanorings. The photoirradiation method is applied to reduce Ag(I) on the plasmid. The nanoparticles are obtained by varying the concentration of the Ag(I) ion solution and the exposure time of the plasmid-Ag(I) complex under UV light at 254 nm and room temperature. It is found that the plasmid serves not only as a template but also as a reductant to drive the silver nucleation and deposition. The resulting nanoparticles have a face-centered cubic (fcc) crystal structure and 20-30 nm average diameter. The detailed mechanism is discussed, and other metals or alloys could also be synthesized with this method.

Slow recombination in quantum dot solid solar cell using p–i–n architecture with organic p-type hole transport material

The interfaces between different materials in the heterojunction colloidal quantum dot (QD) solar cell play an important role for charge carrier separation, recombination and collection. Here, an organic–inorganic hybrid p–i–n architecture for the heterojunction PbS QD solid solar cell is constructed to increase the charge extraction and reduce charge recombination. Heavily doped poly(3-hexylthiophene-2,5-diyl) (P3HT) is applied as hole transport interlayer between the QD film and metal contact electrode. The results show that the P3HT interlayer diminishes the charge carrier recombination at the QD film/metal contact electrode interface leading to increased open-circuit voltage and increased electron life time. Furthermore, after incorporation of P3HT interlayer an additional p–i heterojunction might form at P3HT/QD film interface resulting in increased depletion region, which promotes charge carrier extraction under working conditions. Two other organic p-type interlayers are also investigated, however, the results indicate that a barrier for charge extraction is formed for these devices, which is explained by the difference in energy levels. The solar cell with the P3HT interlayer exhibits a power conversion efficiency of 5.1% at 1 sun of illumination and ambient atmosphere, which is ∼20% higher compared to the solar cell without any hole transport interlayer.

ZnO@Ag2S core-shell nanowire arrays for environmentally friendly solid-state quantum dot-sensitized solar cells with panchromatic light capture and enhanced electron collection

A solid-state environmentally friendly Ag2S quantum dot-sensitized solar cell (QDSSC) is demonstrated. The photovoltaic device is fabricated by applying ZnO@Ag2S core-shell nanowire arrays (NWAs) as light absorbers and electron conductors, and poly-3-hexylthiophene (P3HT) as a solid-state hole conductor. Ag2S quantum dots (QDs) were directly grown on the ZnO nanowires by the successive ionic layer adsorption and reaction (SILAR) method to obtain the core-shell nanostructure. The number of SILAR cycles for QD formation and the length of the core-shell NWs significantly affect the photocurrent. The device with a core-shell NWAs photoanode shows a power conversion efficiency increase by 32% compared with the device based on a typical nanoparticle-based photoanode with Ag2S QDs. The enhanced performance is attributed to enhanced collection of the photogenerated electrons utilizing the ZnO nanowire as an efficient pathway for transporting the photogenerated electrons from the QD to the contact.

DNA assembled single-walled carbon nanotube nanocomposites for high efficiency dye-sensitized solar cells

The performances of photovoltaic devices can be improved by using high electron mobility nanocomposites to increase charge collection and transportation. Single-walled carbon nanotubes (SWNTs) exhibit high electron mobility and are believed to be promising materials to enhance the power conversion efficiency of photovoltaic devices. Herein, we present DNA applied as a biological scaffold to fabricate SWNTs/TiO2 and SWNTs/TiO2/Ag nanocomposites, which are integrated into photoanode films to achieve high efficiency dye-sensitized solar cells (DSSCs). The effects of the amounts of SWNTs and Ag NPs in photoanode films on the performances of DSSCs are investigated. After incorporating the nanocomposites into photoanode films, the power conversion efficiency is enhanced. In particular, when the amounts of SWNTs and Ag NPs in the photoanode are 0.15 wt% and 0.8 wt%, the DSSC exhibits a high power conversion efficiency of ∼5.99%, ∼37.07% improvement compared with conventional TiO2-only DSSCs. The mechanisms of the performance improvement are discussed in detail.

Multi-functional DNA-based synthesis of SWNTs@(TiO2/Ag/Au) nanocomposites for enhanced light-harvesting and charge collection in DSSCs

The performances of photovoltaic devices can be improved by increasing light-harvesting and charge collection respectively. The design and synthesis of nanocomposites with the ability of enhancing the generation and collection of the photo-generated electrons provide a significant way to improve the power conversion efficiency (PCE). Herein, SWNTs@(TiO2/Ag/Au) nanocomposites were synthesized and successfully integrated into photoanode films of dye-sensitized solar cells (DSSCs) to improve the power conversion efficiency. The synthesis processes were based on multi-functional DNA. DNA not only works as a dispersing agent preventing SWNTs bundling but also as a sacrificial mold assembling TiO2, Ag and Au nanoparticles on the surface of the SWNTs. The synthesized SWNTs@(TiO2/Ag/Au) nanocomposites enhance the charge collection and light-harvesting of DSSCs simultaneously. With 2.45 wt% SWNTs@(TiO2/Ag/Au) nanocomposites incorporating into the photoanode films, the PCE of the DSSCs increases from 6.8% to 8.3%.

Super helical Au/TiO2 nanocomposites based on plasmid DNA for efficiency dye-sensitized solar cells

Super helical Au/TiO2 nanocomposites were synthesized using plasmid DNA and incorporated into photoanode of dye-sensitized solar cells (DSSCs). The performance of photoanode films and DSSCs was investigated. Plasmid DNA can not only support as bio scaffold to synthesize Au/TiO2 nanocomposites, but also act as an effective reducing agent under ultraviolet (UV) irradiation. Compared with TiO2-only DSSCs, the light harvesting (LH), corresponding photocurrent and power conversion efficiency (PCE) of DSSCs were enhanced by incorporating of mechanically mixed Au-TiO2 NPs and Au/TiO2 nanocomposites. Compared to the TiO2-only DSSCs samples (5.12%), the PCE of DSSCs with mechanically mixed Au-TiO2 nanoparticles (NPs) (6.41%) increased by 25.20%, and DSSCs with Au/TiO2 nanocomposites (8.17%) increased by 59.57%. The best PCE (8.24%) of DSSCs was obtained with the incorporation of Au/TiO2 nanocomposites. Two reasons were presented for the best performance of DSSCs with Au/TiO2 nanocomposites. Firstly, the localized surface plasmon resonance (LSPR) effect of Au NPs enhanced the absorption visible light. Secondly, the super helical structure of Au/TiO2 nanocomposites provided a path for the transmission of photoelectrons.