Chieh-Hung Yang

Energy-recycling pixel for active-matrix organic light-emitting diode display

The authors report a pixel structure for active-matrix organic light-emitting diode (OLED) displays that has a hydrogenated amorphous silicon solar cell inserted between the driving polycrystalline Si thin-film transistor and the pixel OLED. Such an active-matrix OLED pixel structure not only exhibits a reduced reflection (and thus improved contrast) compared to conventional OLEDs but also is capable of recycling both incident photon energies and internally generated OLED radiation. Such a feature of energy recycling may be of use for portable/mobile electronics, which are particularly power aware.

Plasmonic multilayer nanoparticles enhanced photocurrent in thin film hydrogenated amorphous silicon solar cells

A plasmonic-structure incorporated double layer of Au nanoparticles embedded in the transparent conducting oxide at the back-reflector of the hydrogenated amorphous silicon (a-Si:H) solar cells is demonstrated. These devices exhibit an increase of energy conversion efficiency of 18.4% and short-circuit current density of 9.8% while improving fill-factor and without sacrificing open-circuit voltage. The increase in photocurrent is correlated with the enhanced optical absorption in the cell, with improved optical-path-length by a factor of 7 at the wavelength of 800 nm, due to enhanced diffuse scattering of light through resonant plasmon excitations within Au nanoparticles. In addition to enhanced scattering, applying high-work-function Au nanoparticles can improve the work function match at TCO/a-Si:H interface.

Hydrogenated amorphous silicon solar cell on glass substrate patterned by hexagonal nanocylinder array

The hydrogenated amorphous silicon thin film solar cell fabricated on the glass substrate patterned by hexagonal nanocylinder array prepared by self-assembled SiO2 nanoparticles and nanosphere lithography was investigated. It is demonstrated that the short-circuit current of the patterned solar cell with 65 nm depth nanocylinder increases from 12.3 to 14.4 mA/cm2, and the efficiency increases from 5.18% to 6.59% as compared to the flat solar cell. These phenomena suggest that both effective light trapping and localized surface plasmon lead to significant improvement of light absorption in amorphous silicon solar cells.The hydrogenated amorphous silicon thin film solar cell fabricated on the glass substrate patterned by hexagonal nanocylinder array prepared by self-assembled SiO2 nanoparticles and nanosphere lithography was investigated. It is demonstrated that the short-circuit current of the patterned solar cell with 65 nm depth nanocylinder increases from 12.3 to 14.4 mA/cm2, and the efficiency increases from 5.18% to 6.59% as compared to the flat solar cell. These phenomena suggest that both effective light trapping and localized surface plasmon lead to significant improvement of light absorption in amorphous silicon solar cells.

Hydrogenated Amorphous Silicon Solar Cells on Textured Flexible Substrate Copied From a Textured Glass Substrate Template

It is difficult to prepare textured surface on flexible substrate reproducibly for solar cell application. A novel method is developed that uses polyimide film to coat on a textured glass substrate as a template substrate and then peeled off as the flexible substrate. The surface morphology of the flexible substrate could faithfully reproduce the template as measured by atomic force microscopy. The hydrogenated amorphous silicon (a-Si:H) thin film solar cell was fabricated on the flexible substrate successfully. The results of I-V characteristics and spectral response confirm that the efficiency of textured solar cells increases as compared to that on a flat substrate. This technology will find application in making complicated reusable substrate for flexible electronics.

Localized surface plasmons in Al∕Si structure and Ag∕SiO2∕Ag emitter with different concentric metal rings

This paper reports the optical properties of Al∕Si structure and trilayer Ag∕SiO2∕Ag plasmonic thermal emitter with different concentric metal rings on top metal film. It is found that when the metal width is smaller than 40% of the period (=gap+metal width), the (1,0) Al∕Si surface plasmon leads to a maximum in the transmission spectra; otherwise, the opposite is observed. The dispersion relations and emission spectra of the plasmonic thermal emitters were investigated. The emission peaks are independent of the gap width and redshift as annular metal width increases. This phenomenon suggests the excitation of Fabry-Perot type resonance within cavity of Ag∕SiO2∕Ag structure. No (1,0) Ag∕SiO2 surface plasmon was observed.

Stress Effects on Self-Aligned Silicon Nanowire Junctionless Field-Effect Transistors

The heavily doped n-type silicon nanowire (SiNW) junctionless field-effect transistors (JLFETs) are fabricated using the self-aligned process to control the position and direction of SiNWs. Aligned SiNWs are grown across the prepatterned source and drain under the assistance of the externally applied electric field, which facilitates the subsequent device fabrication. The JLFET exhibits an electron mobility of ~90 cm2/V·s, an on/off ratio of ~107, and a subthreshold slope of ~100 mV/dec. Furthermore, the current variation under stress is investigated. It is shown that stress-induced current change reaches maximum when the JLFET is operated in pinchoff condition. Finally, improvement of off current by 98% and subthreshold swing by 15% using compressive stress of 100 MPa in the n-type JLFET is achieved.

Transmission through randomly arranged microcells of subwavelength holes on an aluminum film

This investigation presents an observation of enhanced optical transmission through an Al film that is perforated with microcells that are arranged in random structures. The dispersion relations of the Al∕p-Si surface plasmon polariton in these structures with individual microcells with 3×3, 6×6, 9×9, 12×12, and 16×16 hole arrays of hexagonal were deduced. The transmission peak wavelength is determined from the spatial period of the microcell arrays. The random structure provides multicolor light transmission, which can be exploited in infrared wavelength-selective devices.

Performance Enhancement of Silicon Nanowire Memory by Tunnel Oxynitride, Stacked Charge Trap Layer, and Mechanical Strain

Heavily doped silicon nanowires (SiNWs) are adopted to fabricate a memory device composed of an AlON tunnel layer and a HfO2/HfAlO charge trap bilayer, which exhibits a large memory window of 4.6 V when operated in the program/erase phases, i.e., +12 V for 100 μs and -12 V for 10 ms, along with excellent 70% extrapolated ten-year data retention and good endurance up to 105 cycles. Strain effects on SiNW memory characteristics have also been investigated. It is demonstrated that the tensile strain increases the program window and the compressive strain improves the data retention. The underlying mechanism is attributed to the incorporation of nitrogen in the AlON tunnel layer.

Improved light scattering in amorphous silicon solar cell by double-walled carbon nanotubes

The application of double-walled carbon nanotubes on amorphous silicon solar cell to improve light trapping and shift the surface plasmon from periodic nanostructure is proposed. A thin film of double-walled carbon nanotubes is coated on the hexagonal nanostructured silver film and uses as the back reflector of solar cells. Based on the periodic Ag nanostructure, the surface plasmon is constructed; with the addition of double-walled carbon nanotubes on the Ag nanostructure, the surface plasmon is red shifted owing to the changing environment around the surface and the light scattering effect is improved due to this rough surface. Our results suggest that by controlling the DWCNTs density on Ag nanostructure, the performance of the short-circuit current and power conversion efficiency can be enhanced‥

Photocurrent enhancements in amorphous silicon solar cells by embedded metallic nanoparticles

In this paper, we report an effective and simple method of enhancing light trapping in a-Si:H solar cells by placing Au nanoparticles at the interface between a-Si:H solar cells and top ITO contact. Compared to a similar cell without embedded Au nanoparticles, a 42.7% increase in energy conversion efficiency and a 49.1% increase in short circuit current density are observed. AFM measurements prove that Au nanoparticles are successfully embedded at the interface between a-Si:H solar cells and top ITO contact.