Artificial lighting for general illumination purposes accounts for over 8% of global primary energy consumption. However, the traditional lighting technologies in use today, i.e., incandescent, fluorescent, and high-intensity discharge lamps, are not very efficient, with less than about 25% of the input power being converted to useful light. Solid-state lighting is a rapidly evolving, emerging technology whose efficiency of conversion of electricity to visible white light is likely to approach 50% within the next years. This efficiency is significantly higher than that of traditional lighting technologies, with the potential to enable a marked reduction in the rate of world energy consumption. There is no fundamental physical reason why efficiencies well beyond 50% could not be achieved, which could enable even greater world energy savings. The maximum achievable luminous efficacy for a solid-state lighting source depends on many different physical parameters, for example the color rendering quality that is required, the architecture employed to produce the component light colors that are mixed to produce white, and the efficiency of light sources producing each color component. In this article, we discuss in some detail several approaches to solid-state lighting and the maximum luminous efficacy that could be attained, given various constraints such as those listed above.

Nano-patterning sapphire substrates technique has been developed for nitrides light-emitting diodes (LEDs) growths. It is expected that the strain induced by the lattice misfits between the GaN epilayers and the sapphire substrates can be effectively accommodated via the nano-trenches. The GaN epilayers grown on the nano-patterned sapphire substrates by a low-pressure metal organic chemical vapor deposition (MOCVD) are characterized by means of scanning electron microscopy (SEM), high-resolution x-ray diffraction (HRXRD) and photoluminescence (PL) techniques. In comparison with the planar sapphire substrate, about 46% increment in device performance is measured for the InGaN/GaN blue LEDs grown on the nano-patterned sapphire substrates.

We implement an accelerated life test for the high-power white LEDs based on spectroradiometric measurement. The luminous flux degradation performances are investigated at both the rated current of 350mA and a higher current of 500mA. The average lifetime of the LEDs is 7057 hours at 350mA and 3508 hours at 500mA. The variations of the color of the white LEDs are studied. The color of the low quality white LEDs changes greatly, while the high quality white LEDs keep their color stable. The degradation performances of the chip and phosphor are studied separately. The quantum efficiency of the phosphor becomes lower from 350mA to 500mA current supply. The LED chip degrades faster than the phosphor during the 500mA high current aging. The luminous flux increase and the peak wavelength shift from 350mA to 500mA current supply are found to be useful lifetime indicating parameters that correlate well to the reliability of the high-power white LEDs.

Thick GaN films were grown on sapphire in a home-made vertical HVPE reactor. Effect of nucleation treatments on the properties of GaN films was investigated, including the nitridation of sapphire, low temperature GaN buffer and MOCVD-template. Various material characterization techniques, including AFM, SEM, XRD, CL and PL have been used to assess these GaN epitaxial films. It was found that the surface of sapphire after high temperature nitridation was flat and showed high density nucleation centers. In addition, smooth Ga-polarity surface of epitaxial layer can be obtained on the nitridation sapphire placed in air for several days due to polarity inversion. This may be caused by the atoms re-arrangement because of oxidation. The roughness of N-polarity film was caused by the huge inverted taper domains, which can penetrate up to the surface. The low temperature GaN buffer grown at 650 °C is favorable for subsequent epitaxial film, which had narrow FWHM of 307 arcsec. The epitaxial growth on MOCVD-template directly came into quasi-2D growth mode due to enough nucleation centers, and high quality GaN films were acquired with the values of the FWHM of 141 arcsec for (002) reflections. After etching in boiled KOH, that the total etch-pit density was only 5×10⁶ cm^-2 illustrated high quality of the thick film on template. The photoluminescence spectrum of GaN film on the MOCVD-template showed the narrowest line-width of the band edge emission in comparison with other two growth modes.

White light was realized through combining a cerium-doped yttrium aluminum garnet (YAG:Ce³⁺) phosphor with a gallium nitride (GaN)-based blue LED. In order to coat the high quality yellow phosphor layer on a GaN chip, the slurry coating technique was focused on because of the speed and coating uniformity. The slurry method is based on a phosphor suspension in a water-soluble photoresist, which is consisted of polyvinyl alcohol (PVA) and ammonium dichromate (ADC). And self-exposure of LED chip was employed as an optimized exposing way to make the photoresist crosslinking. The properties of the phosphor layer in terms of profile, light intensity and uniformity and spectrum were investigated. To improve the qualities of phosphor layer some additives were introduced such as polyvinyl acetate (PVAc) for improving adhesion strength, dispersants and defoamer for uniformity. The thickness of phosphor layer was controlled by altering the time of exposure under UV or blue light. The phosphor pattern with clear margins according to the mask and conformal shape were achieved in different substrates either glasses or LED chips. The white light output of high intensity and good uniformity due to the optimized thickness of phosphor layer were achieved. A defect of photoresist is that the ADC would absorb parts of blue light emitted from LED chip and quench light output, especially in the high concentration, some approaches can be employed to diminish and avoid this defect, such as reduce the ADC's concentration, and find new photosensitizer to replace the ADC.

An effective approach to enhance the light output power of InGaN/GaN light emitting diodes (LED) was proposed using pyramidal patterned sapphire substrates (PSS). The sapphire substrates were patterned by a selective chemical wet etching technique. GaN-based LEDs were fabricated on patterned sapphire substrates through metal organic chemical deposition (MOCVD). The LEDs fabricated on patterned sapphire substrates exhibit excellent device performance compared to the conventional LEDs fabricated on planar sapphire substrates in the case of the same growth and device fabricating conditions. The light output power of the LEDs fabricated on patterned sapphire substrates was about 37% higher than that of LEDs on planar sapphire substrates at an injection current of 20 mA. The significant enhancement is attributable to the improvement of the quality of GaN-based epilayers and improvement of the light extraction efficiency by patterned sapphire substrates.

The structure of micro-LEDs was optimized designed. Optical, electrical and thermal characteristics of micro-LEDs were improved. The optimized design make micro-LEDs suitable for high-power device. The light extraction efficiency of micro-LEDs was analyzed by the means of ray tracing. The results shows that increasing the inclination angle of sidewall and height of mesa, and reducing the absorption of p and n electrode can enhance the light extraction efficiency of micro-LEDs. Furthermore, the total light output power can be boosted by increasing the density of micro-structures on the device. The high-power flip-chip micro-LEDs were fabricated, which has higher quantum efficiency than conventional BALED's. When the number of microstructure in micro-LEDs was increased by 57%, the light output power was enhanced 24%. Light output power is 82.88mW at the current of 350mA and saturation current is up to 800mA, all of these are better than BALED which was fabricated in the same epitaxial wafer. The I-V characteristics of micro-LEDs are almost identical to BALED.

High-power LEDs of different color have generated much enthusiasm because of the potential energy savings and reduced maintenance cost due to long lifetimes compared with traditional light source. Two schemes are widely used for LED dimming: continuous current dimming, or pulse-width modulation (PWM) dimming. The visual felling to the LEDs is the most intuitive judgment in the LED illumination and display. But the apparent brightness of the LEDs under these dimming ways has never been studied. In this paper, the research of the apparent brightness is approached through experiments. The results show that when the average intensities are the same, the apparent brightness of the PWM dimming LED is higher than that of the continuous dimming LED. In addition, to the PWM dimming LEDs, the contrast apparent brightness of various color LEDs is obviously discrepant as the duty cycle is less than 40%, but when it is above 40%, the gap between the contrast values becomes much smaller. Thus, in the LED applications, the LEDs using PWM driving method has higher brightness efficacy, and the duty cycle of the PWM should be above 40% to achieve the consistent apparent brightness between LEDs. The results have great availability to optimize the driver for the LEDs.

In this paper we studied the influence of N electrode on the extraction efficiency of high power light-emitting diodes (LEDs). Simulation and experimental results show that comparing with traditional metal N electrodes the extraction efficiency of LEDs with transparent N electrode is increased by 15%, and it is easier in process than the other techniques. So we proposed a new kind of strip LEDs with transparent electrodes on both P-GaN and N-GaN. The design of transparent electrodes was trade-off between transmittance and resistance. At the same time, the strip structure has some advantages over the traditional square LEDs, which can increase the extraction efficiency and reduce the thermal resistance. Antireflective and high reflective optical coatings were also used in this design. The fabrication of LEDs with transparent electrodes on both P-GaN and N-GaN has been demonstrated. The output power of blue LEDs is 240mW at 350mA, forward voltage is below 3.5V. The luminous flux of white LEDs reached 65lm at 350mA.

The injection and temperature dependence of the spontaneous emission quantum efficiency of molecular beam epitaxy grown InGaAs/GaAs quantum wells is determined using excitation dependent photoluminescence (PL) measurements. The PL measurements were performed at temperatures from 50 to 300 K using a HeNe pump laser with powers ranging from 0.6 to 35 mW. The quantum efficiency is inferred from the power law predicted by the rate equations that links pump power and integrated PL signal. The peak spontaneous emission quantum efficiency of molecular beam epitaxy (MBE) grown InGaAs/GaAs triple quantum wells is determined to be 0.941 at 300K with an overall best value of 0.992 at 100 K.

Different types of dielectric optical coatings for GaN based high bright LEDs were designed and discussed. The optical coatings included the anti-reflection (AR) coating, high-reflection (HR) coating, and omni-directional high reflection coating. Main materials for the optical coatings were dielectric materials such as SiO₂, Ta₂O₅ and Al₂O₃, which were different from the metallic reflector such as Ag usually used now. For the application of anti-reflection coating in GaN LEDs, it was introduced into the design of transparent electrodes with transparent materials such as ITO to form combined transparent electrodes. With the design of P, N transparent electrodes using the AR coating and ITO for GaN LEDs, the extraction efficiency was improved by about 15% experimentally. For the dielectric high-reflection coating, it has higher reflectivity and lower absorption than the metal reflector, and it was supposed to improve the extraction efficiency obviously. While the dielectric omni-directional reflection coating using dielectric materials was also designed and discussed in this article, since which was anticipated to improve the extraction efficiency furthermore. Using SiO₂ and Ta₂O₅, the average reflectivity of a design of all dielectric omni-directional high reflection coating on the sapphire surface was over 94%.

Hall effect, photoluminescence spectroscopy (PL), mass spectroscopy and X-ray diffraction have been used to study bulk ZnO single crystal grown by a closed seeded chemical vapor transport method. Enhancement of n-type electrical conduction and increase of nitrogen concentration are observed of the ZnO samples after high temperature annealing. The results suggest that vacancy is dominant native defect in the ZnO material. These phenomena are explained by a generation of shallow donor defect and suppression of deep level defects in ZnO after the annealing.

Back Light Unit (BLU) and Color Filter are the two key components for the perfect color display of Liquid Crystal Display (LCD) device. LCD can not light actively itself, so a form of illumination, Back Light Unit is needed for its display. The color filter which consists of RGB primary colors, is used to generate three basic colors for LCD display. Traditional CCFL back light source has several disadvantages, while LED back light technology makes LCD obtain quite higher display quality than the CCFL back light. LCD device based on LED back light owns promoted efficiency of display. Moreover it can generate color gamut above 100% of the NTSC specification. Especially, we put forward an idea of Color Filter-Less technology that we design a film which is patterned of red and green emitting phosphors, then make it be excited by a blue light LED panel we fabricate, for its special emitting mechanism, this film can emit RGB basic color, therefore replace the color filter of LCD device. This frame typically benefits for lighting uniformity and provide pretty high light utilization ratio. Also simplifies back light structure thus cut down the expenses.

For improved GaN films on sapphire, GaN nucleation layers (NLs) are typically grown prior to high temperature growth. Using optical reflectance and AFM image analysis we have uncovered mechanistic details of GaN NL evolution during the ramp to high temperature. As the temperature is increased the NL decomposes and GaN nuclei form. We will demonstrate that the GaN nuclei are formed from gas phase Ga atoms generated during the NL decomposition which recombine with ambient NH₃. Continued GaN growth on these nuclei results in GaN films with dislocation densities as low as 4x10⁸ cm^-2. We will show how the NL decomposition kinetics can be extracted from the optical reflectance waveforms and used to control the nuclei formation and growth. More recently we have investigated possible correlations between the GaN nucleation density and the resultant film dislocation density. We have initiated studies of ultra-low (< 10⁷ cm^-2) nucleation densities on sapphire using multi-step NL growth and annealing schemes. We find that over a wide range of nucleation densities that the nucleation density scales quadratically with the NL thickness. The dependence of the dislocation density on the nucleation density is currently being explored.

Hall effect, photoluminescence (PL), infrared absorption, deep level transient spectroscopy (DLTS), and Raman scattering have been used to study property and defects of ZnO single crystal grown by a chemical vapor transport method (CVT). As-grown ZnO is N type with free electron density of 10¹⁶-10¹⁷cm^-3. It has a slight increase after 900°C annealing in oxygen ambient. The DLTS measurement revealed four deep level defects with energy at 0.30eV, 0.50eV, 0.68eV and 0.90eV in the as-grown ZnO sample, respectively. After the high temperature annealing, only the 0.5eV defect survive and has a concentration increase. PL results of the as-grown and annealed ZnO indicate that the well-known green emission disappear after the annealing. The result suggests a correlation between the 0.68eV defect and the green PL peak. Results of P-doped ZnO were also compared with the undoped ZnO sample. The nature of the defects and their influence on the material property have been discussed.

For enhancing the output efficiency of GaN light-emitting diode(LED), we calculated the band structure of photonic crystal(PhC), and designed and fabricated several novel GaN LEDs with photonic crystal on Indium-Tin-Oxide(ITO), which as p-type transparent contact of GaN LED. In this fabricating process, we developed conventional techniques in order that these methods can be easily applied to industrial volume-production. And we have done some preliminary experiments and obtained some results.

Al_xGa_1-xN layer was grown on sapphire substrate with GaN template by Metal Organic Chemical Vapor Deposition system (MOCVD). High temperature AlN (HT-AlN) interlayer was inserted between Al_xGa_1-xN layer and GaN template to solve the cracking problem that often appears on Al_xGa_1-xN surface when directly grown on high temperature GaN template. Optical microscope, scanning electron microscopy (SEM), atomic force microscope (AFM), high resolution x-ray diffraction (HRXRD) and cathodoluminescence (CL) were used for characterization. It was found that the cracking was successfully eliminated. Furthermore, the crystalline quality of Al_xGa_1-xN layer with HT-AlN interlayer was much improved. Interference fringes were found in the HRXRD images. CL test showed that yellow emission was much reduced for AlGaN layer with HT-AlN interlayer.

In this study, effects of n-electrode patterns to the current spreading in the active region were analyzed on the blue vertical light emitting diode (VLED) with GaN/InGaN multi quantum well (MQW). Several n-electrode patterns of the VLED are designed, analyzed qualitatively, and investigated its effect to current spreading in the active region. A 3-dimensinal circuit model whose parameters are experimentally extracted from an actual VLED chip is adopted for the quantitative analysis of current spreading. The n-electrode patterns are modeled and simulated by simple electrical circuits in order to find the current distribution and current-voltage characteristics of devices. Based on theoretical analysis results, blue VLEDs with different n-electrode patterns were fabricated and a series of measurements were carried out. Analytic and experimental results for different n-electrode pattern showed quite similar tendencies. Finally, we proposed some design methodologies for improved current spreading.

We investigate the relation between the thickness of sapphire substrates and the extraction efficiency of LED. The increasing about 5% was observed in the simulations and experiments when the sapphire thickness changed from 100μm to 200μm. But the output power increasing is inconspicuous when the thickness is more than 200μm. The structure on bottom face of sapphire substrates can enhance the extraction efficiency of GaN-based LED, too. The difference of output power between the flip-chip LED with smooth bottom surface and the LED with roughness bottom surface is about 50%, where only a common sapphire grinding process is used. But for those LEDs grown on patterned sapphire substrate the difference is only about 10%. Another kind of periodic pattern on the bottom of sapphire is fabricated by the dry etch method, and the output of the back-etched LEDs is improved about 50% than a common case.

Compared with conventional GaN based LEDs structure, vertical electrodes structure can improve the current uniformity to some extend. However, due to the presence of N-GaN series resistance, current crowing phenomenon still exist at the electrode edge of vertical structure GaN-based LEDs. The most common solutions to overcome these problems consist in using transparent current spreading contact layer, generally made of indium tin oxide (ITO). In this paper, the effect of indium tin oxide (ITO) layer on the current uniformity and the current distribution are analyzed by theoretical calculation. At last, vertical structure GaN-based LEDs was fabricated and the electrical character was measured. Experiment result exhibits good agreement with the theoretical calculation.

All-fiber coupler is a kind of widely utilized passive instrument in optical-fiber communication, optical-fiber sensor, optical-fiber measurement and signal processing, the application of all-fiber couplers are being used in different research fields. In this paper, the primary investigation is focused on the optical coupling theory, and derived from the theory of fused and tapered coupler how to make light apart with the equation of coupled wave. The relative formula between the ratio of power coupling and length of drawing has obtained with simulation using the standard fused and tapered coupler, at the same time the losses and the power distribution of fused and tapered all-fiber coupler are analyzed and computed by simulation. The single-window 1×2 for 1310nm and 1550nm couplers have constructed in experiment, respectively. The couplers' optical parameters of output spectrum and power in theoretical analysis are accorded with the testing standard in experiment.

Currently, to package high power white LED almost use the manner of coating Phosphor over 40mil blue chip, in order to reduce heat dissipation, a new solution was brought about How to integrate small dies to achieve large die effect? This report will bring up a new manner to bond chips in vertical surface, break the traditionary packing manner.

We investigated AlGaN layers grown by metalorganic chemical vapor deposition (MOCVD) on high temperature (HT-)GaN and AlGaN buffer layers. On GaN buffer layer, there are a lot of surface cracking because of tensile strain in subsequent AlGaN epilayers. On HT-AlGaN buffer layer, not only cracks but also high densities rounded pits present, which is related to the high density of coalescence boundaries in HT-AlGaN growth process. The insertion of interlayer (IL) between AlGaN and the GaN pseudosubstrate can not only avoid cracking by modifying the strain status of the epilayer structure, but also improved Al incorporation efficiency and lead to phase-separation. And we also found the growth temperature of IL is a critical parameter for crystalline quality of subsequent AlGaN epilayer. Low temperature (LT-) AlN IL lead to a inferior quality in subsequent AlGaN epilayers.

Patterning sapphire substrate can relax the stress in the nitride epilayer, reduce the threading dislocation density, and significantly improve device performance. In this article, a wet-etching method for sapphire substrate is developed. The effect of substrate surface topographies on the quality of the GaN epilayers and corresponding device performance are investigated. The GaN epilayers grown on the wet-patterned sapphire substrates by MOCVD are characterized by means of scanning electrical microscopy (SEM), atomic force microscopy (AFM), high-resolution x-ray diffraction (HRXRD), and photoluminescence (PL) techniques. In comparison with the planar sapphire substrate, about a 22% increase in device performance with light output power of 13.31 mW@20mA is measured for the InGaN/GaN blue LEDs grown on the wet-patterned sapphire substrate.

The design of microscope field illumination system based on LEDs is demonstrated in this paper. An LED light source, drive circuit, control circuit and collecting lens are included in this system. The light source adopts high brightness white LED array or high power White LED; Area, brightness and angle of the high brightness white LED can be adjusted for the different need of angle of view; Brightness regulation of the high power white LED adopts Pulse-Width Modulation to make the output of brightness is of linearity and stability. In the same condition, the image collected at the LED illumination system compared with the image collected at traditional illumination system. The results shows that this system is of high performance, uniform illumination, good stability; This system is available to satisfy different micro-object and different microscope magnification, and is of great practical value.

The effects of plasma induced damage in different conditions of ICP and PECVD processes on LEDs were presented. For ICP mesa etch, in an effort to confirm the effects of dry etch damage on the optical properties of p-type GaN, a photoluminescence (PL) measurement was investigated with different rf chuck power. It was founded the PL intensity of the peak decreased with increasing DC bias and the intensity of sample etched at a higher DC bias of -400V is less by two orders of magnitude than that of the as-grown sample. Meanwhile, In the I-V curve for the etched samples with different DC biases, the reverse leakage current of higher DC bias sample was obviously degraded than the lower one. In addition, plasma induced damage was also inevitable during the deposition of etch masks and surface passivation films by PECVD. The PL intensity of samples deposited with different powers sharply decreased when the power was excessive. The PL spectra of samples deposited under the fixed condition with the different processing time were measured, indicating the intensity of sample deposited with a lower power did not obviously vary after a long time deposition. A two-layer film was made in order to improve the compactness of sparse dielectric film deposited with a lower power.

Comparing with the conventional CCFL (Cold Cathode Fluorescent Lamp) backlight, three-basic-color LEDs backlight has some advantages such as good color reproduction, long life and lead free etc. Theoretically, the color gamut is determined by x, y coordinates of the three basic colors in CIE chromaticity diagram, and the x, y coordinates of each basic color can derived from the relative spectrum distribution (RSD) of the LED. In this paper, the red, green and blue LEDs' RSD models are established to calculate and analyze the color gamut of a backlight. By simulating those models, the relationships that the color gamut of a LED backlight varies with each color are analyzed, and the optimum combination of three colors is obtained within the given wavelengths ranges. Moreover, the combinations of three colors for the gamut of 115% NTSC and 110% NTSC are plotted in pictures, respectively.

In this paper we present thermal analysis of three different-structured high power LEDs. The thermal resistance of different-structured LEDs was determined. The results indicated that the thermal resistance severely depended on the number of bumps for flip-chip LEDs. One could get lower thermal resistance for flip-chip LEDs than that for conventional and vertical LEDs by selecting appropriate number of bumps in theory. But considering the practical process of LEDs' fabrication, the conventional LEDs because of the simple making process showed more stable and lower thermal resistance. There existed the same problems as flip-chip LEDs' for vertical LEDs. Maybe electroplate copper was the effective way to get good thermal characteristic.

Photon recycling effect has significant influence on the extraction efficiency of LEDs, which active regions possess high spontaneous emission efficiency, i.e. high material quality. Therefore, the conventional definition of internal quantum efficiency should be revised as pointed out by other researchers. In this work, some more detailed considerations of photon extraction efficiency in LEDs are examined using a simple slab structure. Theoretical modeling results show that in order to improve the overall light conversion efficiency, it is necessary to remove the device substrate, to optimize the overall doping profile design, and to use highly reflective metal contacts or DBR structures.

Research and education activities at the School of Photovoltaic and Renewable Energy Engineering at the University of New South Wales (UNSW) are outlined. Research advances are reported for silicon wafer, crystalline silicon thin-film, and third generation technologies. Education activities are also expanding and the School has been fortunate to secure support for sponsorship from 2008 of undergraduate students from selected Chinese universities and postgraduate coursework and research students from China, India and South Korea.

When proceed photovoltaic power system design, engineer needs prepared model of PV cells to evaluate system response, capability performance, and stability, the DC model is not enough, but an accuracy AC model plays a big role. This paper talks first about the AC model of PV cells, and DC model is also introduced in simple. There is a PV controller example explaining the steps to do system simulation in this paper. Two equivalent circuit models are implemented with mixed-signal language verilog-a, one hardware language easy to use and having good speed and high accuracy. Both of two models include solar cell arrays, one buck switched mode DC-DC converter, and the maximum power point tracking algorithm. The difference between them is that Solar cell in one of two models is with ac small signal parameter, another is without. The simulation result is given in comparison. This paper's work shows that ac parameter plays large role in switch-mode PV power system, especially when the switch frequency is higher than 100kHz.

Under high concentration the temperature of photovoltaic solar cells is very high. It is well known that the efficiency and performance of photovoltaic solar cells decrease with the increase of temperature. So cooling is indispensable for a concentrator photovoltaic solar cell at high concentration. Usually passive cooling is widely considered in a concentrator system. However, the thermal conduction principle of concentrator solar cells under passive cooling is seldom reported. In this paper, GaInP/GaAs/Ge triple junction solar cells were fabricated using metal organic chemical vapor deposition technique. The thermal conductivity performance of monolithic concentrator GaInP/GaAs/Ge cascade solar cells under 400X concentration with a heat sink were studied by testing the surface and backside temperatures of solar cells. The tested result shows that temperature difference between both sides of the solar cells is about 1K. A theoretical model of the thermal conductivity and thermal resistance of the GaInP/GaAs/Ge triple junction solar cells was built, and the calculation temperature difference between both sides of the solar cells is about 0.724K which is consistent with the result of practical test. Combining the theoretical model and the practical testing with the upper surface temperature of tested 310K, the temperature distribution of the solar cells was researched.

A procedure for designing and optimizing heliostat field layout of solar tower thermal power plant is developed. The ray tracing is used for the calculation of the optical efficiency of field. The mathematical theory of the calculation is derived. The parametric search algorithm, which allows variation of the field parameters within a specified range, is used for the optimization of field. The field layout is made automatically according to the no-blocking loss condition and the heliostats are located at the positions where the annual incident cosine value is higher. In this way, the blocking and cosine losses are lowered. Because the optimization of the distance between fore-and-aft two rows of heliostat is avoided, the computer time is reduced effectively. Using this procedure the heliostat field of a 1MWe solar tower power plant was designed. Four modes of layout including North-South cornfield, North-South stagger, Radial cornfield and Radial stagger were experimented and optimized respectively. The comparison of the field efficiency for the four optimized results was made. It is concluded that the North-South cornfield layout is the optimal decision for the 1MWe solar tower power plant.

The key factor for high efficiency of tandem Si-based thin film solar cells is to optimize the whole configuration for improving its utilization of solar energy besides the active layers of device-quality level. Several aspects reached in our lab are discussed in this paper. A double structure of P⁺ window layer was proposed and studied. An interlayer between top-cell and bottom-cell in the tandem structure for forming a micro-cavity in top-cell was simulated by the software programmed by ourselves. Finally, the results of two types of tandem solar cells, namely, a-Si/a-Si and a-Si/μc-Si with the light trapping back-reflection structure are reported.

This paper presents a novel design for the controller of the solar-luminaire daylighting system which is fully utilized as the indoor illuminance source with no other power assisted. The controller could precisely trace the sun azimuth to drive reflectors which insure the system collecting the sun light in the most extend, and it is usually worked in the mode of ultra low power consumption via the solar panel, because the low-power consumption method is specially adopted, which realizes green lighting.

Hydrogenated amorphous silicon thin film solar cells are prepared using radio frequency plasma enhanced chemical vapor deposition on polyimide substrates. The structure of the cell is polyimide /Al/n-μc-Si:H/i-a-Si:H/p-a-SiC:H/TCO. Due to amorphous silicon cells have Staebler-Wronski effect and their efficiencies do not stabilize at prepared, so these cells were placed more than fifteen months and I-V characteristics of these cells were measured in four times. They include (i)in the initial, (ii) placed in desiccator over fifteen months, (iii) light-soaked for five hours under AM 1.5 (100mW/cm²) and (iv) annealed for two hours in natural conditions. The measurement results such as open-circuit voltage, short-circuit current, resistance in series, parallel resistance, conversion efficiency and fill factor are given and studied. Staebler-Wronski Effect are found and explained with these parameters. Generally, after light-soaking, the short-circuit currents of cells increase, the fill factors and open-circuit voltage decrease and the reduction of the efficiency is proportional to the fill factor. Abnormal Staebler-Wronski Effect appears in a cell. The cause of these phenomena is analyzed. The consequence that the efficiency varieties with the fill factor is derived r. A graded gap in P-I interface can be improved the cell efficiently. Ultimately, the stability of a-SiH thin film solar cells on polyimide substrate is discussed.

GaSb based cells as receivers in thermophotovoltaic system have attracted great interest and been extensively studied in the recent 15 years. Although nowadays the manufacturing technologies have made a great progress, there are still some details need to make a further study. In this paper, undoped and doped GaSb layers were grown on n-GaSb (100) substrates from both Ga-rich and Sb-rich solutions using liquid phase epitaxy (LPE) technique. The nominal segregation coefficients k of intentional doped Zn were 1.4 and 8.8 determined from the two kinds of GaSb epitaxial layers. Additionally, compared with growing from Ga-rich solutions, the growing processes from Sb-rich solutions were much easier to control and the surface morphologies of epitaxial layers were smoother. Furthermore, in order to broaden the absorbing edge, Ga_1-xIn_xAs_ySb_1-y quaternary alloys were grown on both GaSb and InAs substrates from In-rich solutions, under different temperature respectively.

The effect of interlayer on the performance of a poly[2-methoxy-5-(3',7'-dimethylocty)-1,4-phenylenevinylene] (MDMO-PPV)/1-(3-methoxycarbony 1)-propy1-1 phney1-(6-6)C₆₁ (PCBM) composite solar cell device has been reported recently. Herein we report bulk heterojunction organic solar cell with efficiency enhanced by interlayer made from blend film of regioregular poly(3-hexylthiophene)(P3HT) and PCBM. The interlayer, poly(9,9-dioctylfluorene)-co-N-(1,4-butylphenyl)diphenylamine)(TFB), was inserted between the poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonic acid)(PEDOT:PPS) and the active layer. With the interlayer, the efficiency was enhanced due to the increased short circuit current density (Jsc), open circuit voltage (Voc) and fill factor (FF) obtained from testing and calculation. According to the analysis, the interlayer TFB, acting as an effective exciton-blocking layer, prevented the severe quenching of radiative excitons between the interface of PEDOT:PSS. In the study, the interlayer increased Jsc from 0.891 mA/cm² to 1.025 mA/cm^-2, Voc from 0.478 V to 0.526 V, and FF from 0.327 to 0.416, under illumination by white light from a solar simulator with an incident intensity of 80mW/cm²; the power conversion efficiency of the device reached higher value 0.280% comparing with 0.174% with no interlayer.

This paper (SPIE Paper 68411H) was removed from the SPIE Digital Library on 8 August 2008 upon discovery that the paper has substantially plagiarized the following two papers: R.E. Jones, S.X. Li, L. Hsu, K.M. Yu, W. Walukiewicz, Z. Liliental-Weber, J.W. Ager III, E.E. Haller, H. Lu, and W.J. Schaff, "Native-defect-controlled n-type conductivity in InN," Physica B 376-377 (2006) 436-439 and S.X. Li, K.M. Yu, J. Wu, R.E. Jones, W. Walukiewicz, J.W. Ager III, W. Shan, E.E. Haller, Hai Lu, and William J. Schaff, "Native defects in InxGa1-xN alloys," Physica B 376-377 (2006) 432-435. As stated in the SPIE Publication Ethics Guidelines, "SPIE defines plagiarism as the reuse of someone else's prior ideas, processes, results, or words without explicit attribution of the original author and source, or falsely representing someone else's work as one's own. Unauthorized use of another researcher's unpublished data or findings without permission is considered to be a form of plagiarism even if the source is attributed. SPIE considers plagiarism in any form, at any level, to be unacceptable and a serious breach of professional conduct." It is SPIE policy to remove such papers and to provide citations to original sources so that interested readers can obtain the information directly from those sources. One of the authors, Shao-guang Dong, accepts full responsibility and apologizes for this plagiarism and has absolved the second author, Guang-han Fan, of any prior knowledge of or professional misconduct in this matter. Guang-han Fan also states that he had not previously seen the paper or given permission to include his name as an author.

Disk-shaped molecules can be self-assembled into columns, which may exhibit one-dimensional charge transporting properties within well-oriented domains. They are promising materials to choose in fabrication of organic photovoltaic device and to improve photovoltaic responses. In this work, a discotic triphenylene derivative 2,3,6,7,10,11-hexapentyloxytriphenylene (HAT5) was investigated and used in fabrication of organic photovoltaic devices. The device have a double-layered structure of ITO/HAT5/PTCDI-C₁₃/Al, in which HAT5 acts as an acceptor and hole transporting layer and N,N'-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C₁₃) acts as a donor and electron transporting layer. The device demonstrated an open circuit voltage up to 0.7V, which depended strongly on the thickness of the PTCDI-C₁₃ layer. Function of organic/organic interface to the generation of photovoltaic effect was observed experimentally through a comparison of device made with HAT5 layers of different molecular arrangement. A higher ordered morphology obtained through annealing led to a substantial improvement in the fill factor of the device. A distinct change in open circuit voltage was also observed upon the molecular orientation though it was not what we anticipated. This work demonstrated a useful route to tune the performance of photovoltaic response of organic devices through manipulating molecular orientation and organization in the device.

The time-resolved photoluminescence spectra were investigated on the basis of transmission, reflection and photoluminescence studies of the InGaN single quantum well structure grown by metalorganic chemical vapor deposition. It was found that the temporal responses of photoluminescence decay exhibited exponential function. The multi-peak structure of the photoluminescence spectra was attributed to the Fabry-Perot interference effect in the GaN/InGaN/GaN vertical cavity.

In dye-sensitized solar cells (DSSCs), the physical properties and microstructure of nano-titanium dioxide film electrode are the key factors to influence the photo-electric characters greatly and they are also determined by the preparation techniques. A new electrode of double-layer TiO₂ with different structure was designed and prepared by spin-coating and screen-printing techniques alternately. Such two types of layers have different contribution to the photo-electric conversion functions. Compact TiO₂ film made by spin-coating only absorbs little dyes, but it works as a barrier layer between ITO and electrolyte. The porous TiO₂ film made by screen-printing will absorb more dyes, and results in higher photocurrent. At the end, the effect of the compact layer on I-V properties of the DSSCs was discussed.

This paper gives an overview of the scientific challenges and achievements during the development of thin film silicon based single and tandem solar cells with high-pressure RF-PECVD deposited doped and active layers. The effect of i/p interface treatment on the crystalline growth of high conductive p-type layer and the improvement of the Voc and FF of single-junction a-Si:H solar cell was studied. The role of gradient hydrogen dilution technique in the controlling the microstructural evolution of the intrinsic layer and its influence on the solar cell performance were investigated. By combining above methods, an efficiency of 5.7% (Voc=470mV, Jsc=20.2mA/cm², FF=60%) has been for a single-junction μc-Si:H solar cell. Then, the thicknesses of bottom cells and top cells were varied to achieve good current matching, which yield an efficiency of 9.9% for μc-Si:H/a-Si:H tandem solar cell with Voc of 1221mV, Jsc of 11.61mA/cm² and fill factor of 70%.

A new method for reducing surface reflectance of multicrystalline silicon wafers is presented. The method using holographic lithography and wet etching to fabricate 2-dimensional (2D) photonic crystal (PC) on the surface of multicrystalline silicon. 2D hexangonal PC structures with micron scale lattice constant exhibit significant reduction of the surface reflectance. In the method, 2D hexagonal PC structure is firstly recorded in photoresist, which is coated on the surface of Si wafer, using holographic 3-beam interference technique. After exposure and development the wafer is put into acid solution to transfer the lattice structure into the silicon. Experiments with different exposure angles and etching times were carried out to form different lattice period and structure depth for obtaining optimal lattice parameters. PC with 1.3 μm lattice constant and 0.5 μm depth has achieved a reflectance below 6%. The holographic technique used in the work allows large-area lattice fabrication with only one process. The proposed method has the advantages of low production cost and high throughput, enabling industrial mass production of Si solar cells.

Diffuse processes on the p-type single crystal silicon produced the p-n junction. Porous silicon was prepared by using oxidation etching on the surface of the single crystal with p-n junction. A quantum-sized thin film of TiO₂ was deposited by reactive magnetron sputtering on the p-n junction. The results obtained by the surface photovoltage spectroscope (SPS) showed that the photovoltage of TiO₂/n-Si/p-Si and n-PS/p-PS/Si increase than the photovoltage of n-Si/p-Si. In 300~600 °C, the photovoltage of TiO₂/n-Si/p-Si was enhancing with the rise of temperature, but the photovoltage of TiO₂/n-Si/p-Si was reducing with the rise of temperature in 600~800 °C. The effects of different ion-implantation in single crystal silicon and porous silicon on the photovoltaic characteristics are studied, the photovoltage of argon implanted samples and nitrogen implanted samples was increased a lot beyond the photovoltage of non-implanted samples.

Surface photovoltage spectroscopy (SPS) is used to determine the defect states of the nc-Si:H films which are prepared by using helicon wave plasma-enhanced chemical vapor deposition technique(HWP-CVD) under different substrate temperature. The films exhibit a 3-phase model, which suggests that nc-Si:H consists of crystalline grains surrounded by grain boundaries and embedded in an amorphous matrix. SPS measurement indicated that the nc-Si:H films have additional two types of additional defect states besides the occupied Si dangling bond states D₀/D_i and the empty Si dangling states D₊ in a-Si, which is attributed to the interface defect states between the nanocrystalline Si grains and the amorphous matrix. The relative SPS intensity of these two kinds of defect states in samples increases with the temperature, which may be interpreted as a result of the bonded hydrogen release at the surface of nanocrystalline Si grains and in the amorphou matrix while increasing substrate temperature.