Kien Wen Sun

Biomimetic nanostructured antireflection coating and its application on crystalline silicon solar cells

In this report, we demonstrate the implementation of biomimetic nanostructured antireflection coatings with polymethyl methacrylate (PMMA) layer on the micro-textured surface of silicon crystalline solar cells. To reduce cost, the process combines colloidal lithography, cast molding method, and reversal nanoimprint lithography. The technique is simple, low cost, and does not cause damage to the thin and brittle conventional crystalline solar cells. The antireflection properties of this biomimetic nanostructure coating are considered as effective as those of a conventional single-layer SiNx thin film. The resultant structures alone could reduce the average reflectance of solar cell from 13.2% to 7.8% and enhance power conversion efficiency from 12.85% to 14.2%.

Magnetophotoluminescence properties of Co-doped ZnO nanorods

We present the detailed experimental results of the magnetic and optical properties of cobalt doped ZnO nanorods, especially the temperature and magnetic field dependence of photoluminescence up to 14 T. The Raman measurements indicate that our Co-doped ZnO nanorods have the same lattice constant as crystalline bulk ZnO. Sharp luminescence peaks centered at around 670 nm were observed at low temperature and their intensity decreased with increasing magnetic field. The luminescence peaks were attributed to d-d transitions in the Ligand field from the doped Co ions. We also observed a diamagnetic shift at a temperature of 1.5 K when the magnetic field was scanned from 0 to 14 T. The exciton radius of the Co-doped ZnO nanorods was deduced from the magnetophotoluminescence results.

Highly efficient poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Si hybrid solar cells with imprinted nanopyramid structures

High-efficiency hybrid solar cells based on nanostructured silicon and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), which were fabricated via a simple nanoimprint fabrication process, demonstrated an excellent power conversion efficiency of 10.86%. The complex and costly high-temperature photolithography and masking steps were replaced by techniques that are low-cost and capable of mass production. The nanopyramid structures fabricated on the silicon surface provided an antireflective effect and have a radial junction architecture that enhanced the light absorption and carrier collection efficiency. The short-circuit current density (Jsc) of the hybrid solar cell with nanopyramid structures was greatly improved from 24.5 mA/cm2 to 32.5 mA/cm2 compared with that of a flat surface device. The highest solar cell efficiency was achieved on a 525 μm-thick 2.3 Ω cm n-type Czochralski process (CZ) Si substrate with a designated area of 4 cm2.

Efficiency enhancement of silicon solar cells using a nano-scale honeycomb broadband anti-reflection structure

This experiment demonstrates the process for manufacturing a ZnO honeycomb sub-wavelength structure using nanosphere lithography technology exhibiting excellent anti-reflection properties from the UV to NIR wavelength regions. This honeycomb nanostructure, combined with commercially available crystalline Si solar cells, show substantially improved conversion efficiency from 15.6% to 16.6% using optimized honeycomb sizes and precursor concentrations of ZnO. The present work develops an unsophisticated and economical technique suitable for industrial applications in producing a uniform and low-reflective texture.

Novel pyrene containing monomeric and dimeric supramolecular AIEE active nano-probes utilized in selective “off–on” trivalent metal and highly acidic pH sensing with live cell applications

Two novel pyrene containing monomeric and dimeric Schiff base derivatives PCS1 and PCS2 have been synthesized via one-pot reaction and their nano-J-type aggregation induced emission enhancement (AIEE) was well demonstrated using UV-Vis/PL, transmission electron microscopy (TEM), dynamic light scattering (DLS), time resolved photoluminescence (TRPL), and live cell imaging studies. In contrast to PCS2, PCS1 in CH3CN exhibits fluorescence “off–on” sensor selectivity towards transition trivalent metal ions (Fe3+, Cr3+ and Al3+) among other metals, via PET inhibition with excimer PCS1–PCS1* formation. The 2 : 1 stoichiometry of PCS1⋯M3+ (M = Fe/Cr/Al) sensor complexes was calculated from Jobs plots based on their PL titrations. In addition, the binding sites of PCS1⋯M3+ sensor complexes were well recognised from the 1H NMR titrations and supported by ESI(+ve) mass and FTIR analysis. Additionally, fluorescence reversibilities of PCS1⋯M3+ were observed via consequent addition of M3+ ions and PMDTA, respectively. Furthermore, the detection limits (LODs) and the association constant (Ka) values of PCS1⋯M3+ complexes were calculated using standard deviation and linear fittings. Likewise, quantum yield (Φ) measurements, TEM analysis, determination of the effect of pH, density functional theory (DFT) and time resolved photoluminescence (TRPL) studies were performed for the PCS1⋯M3+ sensor complexes. More importantly, confocal fluorescence microscopy imaging of Raw264.7 cells showed that PCS1 could be used as an effective fluorescent probe for detecting transition trivalent metal ions (Fe3+, Cr3+, and Al3+) in living cells. Impressively, both PCS1 and PCS2 showed “off–on” sensing at highly acidic pH values (1–3) with live cell applications.

Raman spectroscopy of single nanodiamond: Phonon-confinement effects

In this paper, we devise techniques for immobilizing and allocating a single nanodiamond on the electron beam (e-beam) patterned smart substrate. The properly designed coordination markers on the semiconductor substrate and the high throughput of the confocal microscope provide us with a convenient tool to single out a nanodiamond with a size less than 100nm and to study Raman spectroscopy. We observe a redshift in energy and broadening in the linewidth of the sp3 bonding Raman peak when the size of the diamond is decreased from 90to35nm. The observed shifts and linewidth broadening arise from the phonon-confinement effects and are in good agreement with calculations reported by [Ager et al. Phys. Rev. B 43, 6491 (1991)] and [Yoshikawa et al. Appl. Phys. Lett. 62, 3114 (1993)].

Ultrafast carrier capture and relaxation in modulation-doped InAs quantum dots

We report investigations on carrier capture and relaxation processes in undoped and modulation-doped InAs∕GaAs self-assembled quantum dots (QDs) by using time-resolved spectroscopy technique with a time resolution of ∼200fs. We find that carrier capture and relaxation in the ground state of the charged QD are faster compared to the undoped dots even at an excitation level as low as 1×1010cm−2. It is attributed to the triggering of the vibrating polarization field induced by the presence of cold carriers in the doped dots. The rate of an electron been captured by a positively charged QD is also calculated based on our proposed model.

Protein Functionalized Nanodiamond Arrays

Various nanoscale elements are currently being explored for bio-applications, such as in bio-images, bio-detection, and bio-sensors. Among them, nanodiamonds possess remarkable features such as low bio-cytotoxicity, good optical property in fluorescent and Raman spectra, and good photostability for bio-applications. In this work, we devise techniques to position functionalized nanodiamonds on self-assembled monolayer (SAMs) arrays adsorbed on silicon and ITO substrates surface using electron beam lithography techniques. The nanodiamond arrays were functionalized with lysozyme to target a certain biomolecule or protein specifically. The optical properties of the nanodiamond-protein complex arrays were characterized by a high throughput confocal microscope. The synthesized nanodiamond-lysozyme complex arrays were found to still retain their functionality in interacting with E. coli.

Plasmon-enhanced photoluminescence from bioconjugated gold nanoparticle and nanodiamond assembly

In this letter, we coupled nanodiamonds (NDs) with gold nanoparticles of different sizes using two complementary DNA sequences. After hybridizing the gold nanoparticles on the NDs, we observed the enhancement of the photoluminescence (PL) signals originating from the nitrogen-vacancy (N-V) center of the ND. The enhancement was attributed to the plasmon field created by the gold nanoparticles. The line shape of the enhanced PL spectra was also affected by the sizes of the attached nanoparticles due to their different resonant plasma frequencies. The signal enhancement can be used as an indexing tool for biosensing applications.

Selective growth of single InAs quantum dots using strain engineering

A method to achieve ordering and selective positioning of single InAs self-assembled quantum dots (QDs) has been developed. The selective growth was achieved by manipulating the strain distribution on the sample surface. The QDs are formed on predesigned mesas with added strain. Single dots were obtained on small mesas. Using this technique, two-dimensional single QD arrays have been achieved.