-
[show abstract]
[hide abstract]
ABSTRACT: Radial heterojunction photodiodes based on a silicon nanowire arrays (SiNWs)-zinc oxide (ZnO) core-shell structure is demonstrated in this report. The heterojunction can be constructed by spin-coating ZnO nanoparticles onto SiNWs and a low temperature post-annealing process (<270 °C). The photodiode displays typical diode rectifying characteristics with an ideality factor of as low as 1.28, and shows an excellent photoresponse in both visible and near infrared regions in which a peak value of 0.54 A/W at zero bias was attained. The sensitivity is superior to that of previously reported devices fabricated with vacuum-deposition methods. In contrast, the planar silicon-ZnO junction only displays the peak photoresponsivity of 0.34 A/W. The superior performance of radial junction is ascribed to the highlight-harvesting capability, large interfacial area and efficient charge carrier collection arising from the core (SiNWs)-shell (ZnO) structure. Here, high temperature processes are dispensable by using facile solution-processed techniques, which avoid thermal minority lifetime degradation of silicon and simplify the fabrication process of the photodiodes.
Physical Chemistry Chemical Physics 02/2013; · 3.57 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Silicon nanowire arrays (SiNWs) on a planar silicon wafer can be fabricated by a simple metal-assisted wet chemical etching method. They can offer an excellent light harvesting capability through light scattering and trapping. In this work, we demonstrated that the organic-inorganic solar cell based on hybrid composites of conjugated molecules and SiNWs on a planar substrate yielded an excellent power conversion efficiency (PCE) of 9.70%. The high efficiency was ascribed to two aspects: one was the improvement of the light absorption by SiNWs structure on the planar components; the other was the enhancement of charge extraction efficiency, resulting from the novel top contact by forming a thin organic layer shell around the individual silicon nanowire. On the contrary, the sole planar junction solar cell only exhibited a PCE of 6.01%, due to the lower light trapping capability and the less hole extraction efficiency. It indicated that both the SiNWs structure and the thin organic layer top contact were critical to achieve a high performance organic/silicon solar cell.
Journal of the American Chemical Society 12/2011; 133(48):19408-15. · 9.91 Impact Factor
-
Xiaojuan Shen
[show abstract]
[hide abstract]
ABSTRACT: The left-handed beta-helix (LβH) has received interest recently as it folds as a possible solution for the structure of misfolded proteins associated with prion and Huntington's diseases. Through a combination of sequence and structure analysis, we uncover a novel feature that is common to this unique fold: a two-fold symmetry in both sequence and structure, and this feature always coupled with extended loops in the middle of the helix. Since the results reveal a two-fold symmetric pattern both in the sequence and structure, it may indicate that the symmetry in tertiary structure is coded by the symmetry in primary sequence, which agrees with Anfisen's proposal that a protein's amino-acid sequence specify its three-dimensional structure. It may also indicate that LβH adopts a two-fold repeat pattern during the evolution process and symmetry helps maintaining the stability of the helix structure. The two-fold symmetric pattern and extended loops might be important in maintaining stability of helix proteins. This discovery can be useful in understanding the folding mechanisms of this protein fold and provide insights in the relation between sequences and structures.
Journal of Theoretical Biology 06/2011; 285(1):77-83. · 2.21 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Photoelectrochemical (PEC) cells based on silicon nanowire arrays (SiNWs) have, to date, exhibited modest power conversion efficiency (PCE) and suffered serious degradation, though they exhibit advantageous properties of charge-transfer/transport properties at the radial-junction and strong light-trap capabilities. The main challenge for this low-cost PEC cell is the surface photooxidation and photocorrosion of the silicon surface when contacting with the electrolyte. In this report, SiNWs derivatized with covalently attached methyl groups, prepared via a two-step chlorination/methylation procedure, demonstrate excellent stability even in the presence of water. Furthermore, SiNWs PEC cells utilizing a room temperature ion liquid (IL) acting as an electrolyte solvent display neglectable surface oxidation. A PEC cell based on a platinum (Pt) nanodots decorated and methylated (-CH(3)) SiNWs electrode in combination with an IL electrolyte yields a PCE of 6.0% and shows excellent stability under simulated air mass (AM) 1.5 solar spectrum irradiation, while the PCE of a PEC cell based on planar silicon only exhibits 0.003%. The inherent performance of these structures indicates that a -CH(3) (Pt) SiNWs electrode in combination with an IL is a new approach to develop a high-performance and low-cost solar cell.
ACS Nano 10/2010; 4(10):5869-76. · 10.77 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate the fabrication of light-emitting diodes (LEDs) made from all-inorganic colloidal semiconducting nanocrystals (NCs). The diode utilizes a sandwich structure formed by placing CdSe/CdS NCs between two layers of Si and Ag <sub> x </sub> O , which act as electron- and hole-transporting materials, respectively. The photoluminescence properties of NCs are rendered less dependent upon surface chemistry and chemical environment by growing a thick CdS shell. It also enhances stability of the NCs during the process of magnetron sputtering for silicon deposition. The resulting LED device exhibits a low turn-on voltage of 2.5 V and the maximum external quantum efficiency of nearly 0.08%.
Applied Physics Letters 01/2010; · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Exciton dissociation and carrier transport in poly(3-hexylthiophene) (P3HT)/germanium (Ge) nanocrystals composites were investigated by steady-state and time-resolved photoluminescence (PL) as well as photovoltaic (PV) effect. Quenching of the PL quantum yield η and shortening of the PL lifetime τ in the composites were observed, which were ascribed to rapid exciton dissociate at the interface. PV devices were fabricated based on Ge/P3HT composites sandwiched between indium tin oxide and aluminum. The external quantum efficiency spectrum displayed wide photoresponse range, covering both nanocrystals absorption range and P3HT one. Large open circuit voltage up to 0.45 V and obvious short-circuit current were demonstrated in hybrid Ge nanocrystals/P3HT PV device.
Applied Physics Letters 06/2009; 94(23):233504-233504-3. · 3.84 Impact Factor
