Hsun-Wen Wang

Enhanced efficiency for c-Si solar cell with nanopillar array via quantum dots layers.

The enhanced efficiency of the crystalline silicon (c-Si) solar cell with nanopillar arrays (NPAs) was demonstrated by deployment of CdS quantum dots (QDs). The NPAs was fabricated by the colloidal lithography and reactive-ion etching techniques. Under a simulated one-sun condition, the device with CdS QDs shows a 33% improvement of power conversion efficiency, compared with the one without QDs. For further investigation, the excitation spectrum of photoluminescence (PL), absorbance spectrum, current-voltage (I-V) characteristics, reflectance and external quantum efficiency of the device was measured and analyzed. It is noteworthy that the enhancement of efficiency could be attributed to the photon down-conversion, the antireflection, and the improved electrical property.

Synthesis design of artificial magnetic metamaterials using a genetic algorithm

In this article, we present a genetic algorithm (GA) as one branch of artificial intelligence (AI) for the optimization-design of the artificial magnetic metamaterial whose structure is automatically generated by computer through the filling element methodology. A representative design example, metamaterials with permeability of negative unity, is investigated and the optimized structures found by the GA are presented. It is also demonstrated that our approach is effective for the synthesis of functional magnetic and electric metamaterials with optimal structures. This GA-based optimization-design technique shows great versatility and applicability in the design of functional metamaterials.

Conversion Efficiency Enhancement of GaN/In

In this study, p-i-n double-heterojunction GaN/ In0.11Ga0.89 N solar cells grown by metal-organic chemical vapor deposition on pattern sapphire substrate are presented. The solar cell with standard process has a conversion efficiency of 3.1%, which corresponds to a fill factor of 58%, short circuit current density of 2.86 mA/cm2 , and open circuit voltage of 1.87 V under AM1.5G illumination. To further improve the conversion efficiency of the GaN/ In0.11Ga0.89 N solar cells, two-dimensional polystyrene nanospheres were deposited and self-organized as mask in the anisotropic inductively coupled plasma reactive ion etching process to form a biomimetic surface roughing texture. The surface morphology of the solar cell shows a periodically hexagonal bead pattern and the beads are formed in a diameter of 160 nm with a period of 250 nm. An increase of 15% in short circuit current density is found, thus improving the conversion efficiency to 3.87%. If we optimize the structure for 180 nm of the height and 375 nm of the period, a 10% gain can be expected when compared to the current structure.

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Traditional p-GaN/i-InGaN/n-GaN double heterojunction solar cells have limited power conversion efficiency due to large polarization charges that accumulate at the heterojunction interfaces, leading to severe band bending that, in turn, hinders the carrier transport. In this study, we proposed the use of a p-type InGaN layer to reduce the polarization field and projected the power conversion efficiencies of p-In xGa1-xN/i-In yGa1-y N/n-GaN double heterojunction solar cells that are grown on a c-facet sapphire substrate with various indium components. Numerical simulations predict that a maximal power conversion efficiency that is close to 7% with a short-circuit current density of 4.05 mA/cm2 and an open-circuit voltage of 1.94 V can be achieved with a p-In0.2 Ga0.8N/i-In0.2Ga0.8N/n-GaN structure due to a polarization-matched p-i interface. Further efficiency enhancement with a higher indium composition over 20% is also possible via the redistribution of the built-in potential with n-GaN doping.

Ga

The enhanced light extraction and reduced forward voltage of a GaN-based vertical injection light emitting diode (VI-LED) with an indium–tin-oxide (ITO) nanorod array were demonstrated. The ITO nanorod array was fabricated by the glancing-angle deposition method. The employment of ITO nanostructures amplified not only the broadband transmission but also the current spreading. The optical output power of GaN-based VI-LEDs with ITO nanorods was enhanced by 50% compared with a conventional VI-LED at an injection current of 350mA. The extraction efficiency was dramatically raised from 62 to 93% by the surface ITO nanorods. We also optimized the extraction efficiency of the GaN-based VI-LED with an ITO nanorod array by tuning the thickness of the n-GaN top layer via three-dimensional finite difference time domain (3D-FDTD) simulation. # 2011 The Japan Society of Applied Physics

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A single-junction InGaP solar cells with polystyrene (PS) nanospheres on the surface has been developed. The self-assembly of PS nanospheres is one of the simplest and the fastest methods with which to build a 2D closely packed periodic structure. Based on the scattering of the PS nanospheres, the light path length can be increased. As compared to the InGaP solar cells without PS nanospheres on the top surface the standard process. An increase short-circuit current form 8.93% to 10.31% is improved when a single-junction InGaP solar cells with PS nanospheres. The conversion efficiency measured can also be improved from 8.79% to 9.71%. The single-junction InGaP solar cell with PS nanospheres was achieved.

N Solar Cells With Nano Patterned Sapphire and Biomimetic Surface Antireflection Process

The enhanced photoelectric conversion is demonstrated in nanostructured glass substrates for a-Si thin film solar cell. The nanostructured glass substrates were fabricated using nanosphere lithography and RIE technique. The nanostructure substrates provide antireflective and light scattering characteristics, which enhance the broadband light absorption, especially in near-infrared range. Finally we demonstrate the patterned glass substrates (nipple shape arrays) which are useful in light absorption of a-Si thin film solar cell. Compared to a flat glass substrate cell and Asahi-U glass substrate cell, the power conversion efficiency enhancement achieved 48.4% and 3.1%, the Jsc enhancement achieved 51.6% and 8%.

Projected Efficiency of Polarization-Matched p-In

The photovoltaic properties of 14 pairs In₀₁₅Ga_0.85N/GaN multiple quantum well solar cells with varying indium composition of QW are investigated numerically. The simulation results show that smooth well structure of energy band can be reduce carrier confinement and the recombination to enhance photo-current generation. This helpful design is easy to improve carrier transport to collection. And the optimal In₀₁₅Ga_0.85N/GaN MQW solar cell had V_oc of 2.37V, J_sc of 0.73, and the efficiency of 0.79%, which the efficiencies is enhanced 69.2 % to reference cell.

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The influence of band structure and indium composition of stepping layer are numerically investigated on the photovoltaic characteristics of InGaN/GaN MQW solar cell. In this study, the barrier structure and indium composition of inserting stepping layer leads to a substantial influence in the cell efficiency and output short circuit current density. It reveals that L-structure in barrier modulation would contribute to fine carrier collection and increase the conversion efficiency. Moreover, L-structure barrier modulation would effectively reduce the recombination rate in wells near p-GaN side where dominant recombination in well regions is. Barrier height of stepping layers plays an important role in high carrier collection that keeps high conversion efficiency. However, the optimal 5% indium composition of L-structure 14-pair MQW solar cell would obtain the best performance.

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The characteristics of non-polar double heterojunction GaN/ In_xGa_1-xN solar cells with various indium contents are numerically investigated. By smoothing the interface band edge offset with graded junction, the maximum efficiency reached 24.32 % as In_0.6Ga_0.4N.