In order to fabricate AZO/SiO2/p-Si heterojunction device and let it be an absorber of ultraviolet response cell. Zinc oxide (ZnO) thin films doped with aluminum (AZO) were deposited on p-Si(100) substrates covered with silicon dioxide (SiO2) by radio frequency magnetron sputtering. The optical and electrical properties of the Al doped - ZnO films were characterized by UV-VIS spectrophotometer, current-voltage measurement, and four point probe technique, respectively. The results show that the device is a typical tunneling diode for minority carrier and a strong obstructing effect from majority carriers. The potential rectifying behavior and photovoltaic characteristic is present at dark current and weak light illumination, respectively.

Field-Assisted Simultaneous Synthesis and Transfer (FASST®) process offers a controllable and cost-effective method to produce Copper Indium Gallium Selenide (CIGS) films for high efficiency photovoltaic devices. In the first stage of the two-stage FASST® process two separate precursor films are formed, one deposited on the substrate and the other on a reusable printing plate. In the second stage, the precursors are brought into intimate contact and rapidly reacted under pressure in the presence of an applied electrostatic field, effectively creating a sealed micro-reactor that ensures high material utilization efficiency, direct control of reaction pressure, and low thermal budget. The unique ability to control both precursor films independently allows for composition and deposition technique optimization, eliminating pre-reaction prior to the synthesis of CIGS. This flexibility has proven immensely valuable as is demonstrated in the results of depositing the two-reactant films by various combinations of low-cost solution-based and conventional vacuum-based physical vapor deposition techniques, producing in several minutes' high quality “hybrid” CIGS with large grains on the order of several microns. Cell efficiencies as high as 12.2% have been achieved using the FASST® method.

A metal-induced growth (MIG) process was employed to deposit thin films of microcrystalline silicon (μc-Si) for solar cell applications. Due to different grain orientations of the crystals, the absorption coefficient of μc-Si is about 10 times higher than the absorption coefficient of single crystalline Si. The properties of the Si film were investigated resulting from variations in several parameters. A range of Ni and Co thicknesses were examined from 7.5 nm to 60 nm including combinations of the two, while the dc sputtering power was stepped up from 150 W to 225 W. The structure of the resulting film was studied using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD). SEM of the film revealed that 5 hr of Si deposition at 150 W yields a film thickness of 6.5 μm and a maximum grain size of about 0.6 μm. EDS data showed that at the middle of the Si film the atomic percentage of the Si was 99.17%. XRD data showed that the dominant crystal orientation is {220}. To characterize the photovoltaic properties of the μc-Si, Schottky photodiodes were fabricated. Ni alone as the seed layer resulted in ohmic behavior. With Co only, MIG formed a rectifying contact with open-circuit voltage (V∝). The combination of Co layered over Ni formed better thin films and gave a Voc of 0.24 V and short-circuit current density (Jsc) of 5.0 mA/cm2 since the Co prevents Ni contamination of the top of the grown Si layer.

This work reports on the fabrication and characterization of Mo thin films on soda-lime glass substrate grown by reactive RF magnetron sputtering. Film thickness was measured by x-ray step surface profiler. The structural properties and surface morphology were analyzed by x-ray diffraction (XRD), atomic force microscope (AFM) and scanning electron microscopy (SEM). Electrical properties were measured by four-point probe. It was found that the growth parameters, such as argon flow rate, RF power, film thickness, have significant influences on properties of Mo films. The strain on films revealed the complicated relationship with the working pressure, which might be associated with micro structures and impurities. In order to improve the adhesion and electricity, we adopted a two-pressure deposition scheme. The optimal thickness and sheet resistance are νm and 0.12 ω The mechanisms therein will be discussed in detail. Furthermore, we also investigated the diffusion property of Na ion of double Mo films sputtered on soda-lime glass. Our experimental results could lead to better understanding for improving further CIGS-based photovoltaic devices.

Short-bandgap group II-VI compound cadmium telluride is widely used for the infrared optics, radiation detectors, and solar cells where p-type CdTe is needed. p-type conductivity of CdTe is mainly caused by the chlorine-based A-centers, and in part, by the less stable copperoxygen complexes. As a rule, CdTe films are recrystallized by the help of a cadmium chloride flux that saturates CdTe with chlorine. In chlorine-saturated CdTe A-centers are converted to isoelectronic complexes that cause resistivity increasement of CdTe up to 9 orders of magnitude. Excess copper and oxygen or group I elements as sodium also deteriorate the p-type conductivity of CdTe like excess chlorine. p-type conductivity of CdTe can be restored e.g. by the vacuum annealing which removes excess chlorine from the film. Unfortunately, treatment that betters ptype conductivity of the CdTe film degrades the junction of the superstrate configuration cells. In this work we investigate possibilities to prepare p-type CdTe films on the molybdenum coated glass substrates. Samples were prepared by the vacuum evaporation and dynamic recrystallization of 6N purity CdTe on the top of Mo-coated glass substrates. Then samples were recrystallized with cadmium chloride flux under tellurium vapour pressure. Results of the test studies on the structure and electronic parameters of samples are presented and discussed.

InGaN alloys are widely researched in diverse optoelectronic applications. This material has also been demonstrated as a photovoltaic material. This paper presents the study to achieve optimum electrically active p-type InGaN epi-layers. Mg doped InGaN films with 20% In composition are grown on GaN templates/sapphire substrates by MOCVD. It is found that the hole concentration of p-type InGaN depends strongly on the Mg flow rate and V/III molar ratio and hole concentration greater than 2×1019 cm−3 has been achieved at room temperature. The optimum activation temperature of Mg-doped InGaN layer has been found to be 550-600°C, which is lower than that of Mg-doped GaN. A solar cell was realized successfully using the InGaN epi-layers presented here.

In order to achieve the widespread use of HIT (Hetero-junction with I etero-Intrinsic T ntrinsic Thin-layer) solar cells, it is important to reduce the power generating cost. There are three main approaches for reducing this cost: raising the conversion efficiency of the HIT cell, using a thinner wafer to reduce the wafer cost, and raising the open circuit voltage to obtain a better temperature coefficient. With the first approach, we have achieved the highest conversion efficiency values of 22.3%, confirmed by AIST, in a HIT solar cell. This cell has an open circuit voltage of 0.725 V, a short circuit current density of 38.9 mA/cm2 and a fill factor of 0.791, with a cell size of 100.5 cm2. The second approach is to use thinner Si wafers. The shortage of Si feedstock and the strong requirement of a lower sales price make it necessary for solar cell manufacturers to reduce their production cost. The wafer cost is an especially dominant factor in the production cost. In order to provide low-priced, high-quality solar cells, we are trying to use thinner wafers. We obtained a conversion efficiency of 21.4% (measured by Sanyo) for a HIT solar cell with a thickness of 85μm. Even better, there was absolutely no sagging in our HIT solar cell because of its symmetrical structure. The third approach is to raise the open circuit voltage. We obtained a remarkably higher Voc of 0.739 V with the thinner cell mentioned above because of its low surface recombination velocity. The high Voc results in good temperature properties, which allow it to generate a large amount of electricity at high temperatures.

For realizing the proof of mass production capablity or a move toward a GW/a production, 16%-efficiency project has been started setting the target of each parameter as V∝: 0.685 V/cell, FF: 0.735 and Jsc: 31.8mA/cm2. Up to FY2008, the target of each parameter independently has been achieved expect the efficiency. All of our research by adjusting the two resistance (Rsh and Rs) in the monolithically integrated 30cm×30cm-sized circuits. To improve the FF, double buffer structure with CBD-Zn(O,S,OH)x and MOCVD-ZnO is proposed and the thickness is adjusted by optimizing the Rs and the Rsh. As the result, FF of over 0.7 has been achieved for the first time in our CIS R&D since FY 1993.

Plasma immersion ion implantation (PIII) is a technique of material processing and surface modification, using controllable negative high voltage pulsed bias to attract the ion generated from the plasma. The method using PIII treatment quickly improves the performance of solar cell made of crystalline silicon, including monocrystalline, multicrystalline and polycrystalline silicon. Hydrogen ions are attracted and quickly implanted into solar cell under a predetermined negative pulse voltage, thus, the passivation of the crystal defects of the solar cell can be realized in a short period. Meanwhile, the properties of the antireflection layer can not be damaged as the proper operating conditions are used. Consequently, the series resistance can be significantly reduced and the filling factor increases as a result. Both the short-circuit and the open-circuit voltage can be increased. The efficiency can be enhanced.

Photovoltaic devices based on soluble conjugated polymers have gained great interest in recent years because of the potential low cost of production and ease of fabrication. PCBM ([6,6]-phenyl-C61-butyric acid methyl ester), a fullerene derivative, has been extensively investigated as a solution processable electron acceptor for bulk-heterojunction (BHJ) photovoltaic devices blended with conjugate polymers like P3HT [poly(3-hexylthiophene)]. Here, we investigated a novel solution processable organic semiconductor, C60(CN)2, as an electron acceptor for bulk heterojunction photovoltaic applications. Optical and electrical properties of C60(CN)2 are studied and compared with PCBM. Blend devices with P3HT and C60(CN)2 have been fabricated and compared with P3HT-PCBM devices. The effect of thermal annealing on the device performance is evaluated. Open circuit voltage, short circuit current, fill factor and total efficiency data are compared with PCBM based devices.

A novel ultrafast laser texturing method has been developed to produce arrays of nano/micro surface textures in silicon. Laser processing conditions have been optimized for achieving appropriate optical and electronic properties for photovoltaic applications. The textured silicon surfaces absorb greater than 99% of incident light over the entire solar spectrum and the material appears complete black to bare eye. Textured silicon surfaces are characterized for surface morphology and optical properties. Chemical etching and thermal annealing steps have been performed to remove laser slag and induced defects. Finally, we report the total and external quantum efficiency results on photovoltaic devices fabricated on the textured silicon wafers, which can be further improved.

We report the growth of Cu2ZnSnS4 (CZTS) thin films by electrodeposition in ionic liquid. Sulfurization was performed in elementary sulfur vapor environment at 450°C for 2 hours. The X-ray diffraction analysis indicated that the film has a stannite structure with preferred grain orientation along (112). Photo-absorption measurement of the sample was performed from 500 nm to 990 nm. It is found that the energy bandgap of the film is about 1.49eV and the absorption coefficient is found to be of the order of 104cm-1.

The calibration factors are examined for determination of boron (B) and phosphorus (P) in solar grade silicon samples in the new generation of high resolution fast-flow glow-discharge mass spectrometers (FF-GDMS). It is shown that using the generalized calibration factors from the Standard RSF table, the relative errors observed in the determination of these analytes is not acceptably small for photovoltaic applications. The certified B and P values in NIST SRM 57a Si metal sample do not have the confidence intervals, which would be adequate for refining these calibration factors to the acceptable levels. Thus, well-characterized single crystalline Si wafers with known boron and phosphorus contents traceable to NIST reference materials (SRM 2133 and SRM 2137) were used for accurate calibrations and for establishing good analytical procedures for measurements of wide variety of Si sample forms. The obtained results for these important analytes using the new FF-GDMS procedure are compared to other characterization techniques commonly used in this industry.

This paper is a case study of using SIMS to quantitatively measure C, O and N impurity contamination at two sequential commercial process steps: (1) Si feedstock: 7N (modified Siemens) and 5N feedstock (UMG-Si); and (2) multi-crystalline (mc-Si) solar wafers: cut and etched, from directional solidification bricks grown from 7N and 7N/5N (80:20) feedstock. The conclusion of this study is twofold: (a) the primary opportunity to reduce C, O and N contamination in mc-Si solar cells is at the directional solidification process, and (b) the costly specification of highly pure Si feedstock is unnecessary from a C, O and N perspective if a directional solidification process is used.

The major factor limiting the efficiencies of thin film Si solar cells is their weak absorption of red and near-infrared photons due to short optical path length and indirect bandgap. Powerful light trapping is essential to confine light inside the cell for sufficient absorption. Here we report the first experimental application of a new light trapping scheme, the textured photonic crystal (TPC) backside reflector, to monocrystalline thin film Si solar cells. TPC combines a onedimensional photonic crystal, i.e., a distributed Bragg reflector (DBR), with a reflection grating. The near unity reflectivity of DBR in a wide omnidirectional bandgap and the large angle diffraction by the grating ensures a strong enhancement in the absorption of red and near-infrared photons, leading to significant improvements in cell efficiencies. Measured short circuit current density Jsc was increased by 19% for 5 μm thick cells, and 11% for 20 μm thick cells, compared to theoretical predictions of 28% and 14%, respectively.

We have utilized room-temperature solvent vapor treatment followed by thermal annealing to process bulk heterojunction (BHJ) photovoltaic devices based on blends of poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) of varied active layer thickness. The morphological and photovoltaic performance characteristics of the cells subject to these treatments were found to be dependent on active layer thickness. The devices were characterized using atomic force microscopy (AFM) and opto-electrical and external quantum efficiency measurements in order to analyze the mechanism underlying the observed trend. Performance indicators including fill factor, short-circuit current and power conversion efficiency were correlated to the ordering of device active layers and morphology. The maximum power conversion efficiency achieved was 4.1 %.

Behavior of oxygen, carbon and minority-carrier lifetimes of multi-crystalline silicon (mc-Si) has been investigated by means of FTIR and QSSPCD after three step annealing. For comparison, the annealing of czochralski (CZ) silicon was also carried out under the same conditions. The results revalted that oxygen and carbon concentration pf mc-Si had a larger decrease than that of CZ -Si, which means the more oxygen precipitates in mc-Si were generated. High density defects of mc-Si such as grain boundaries and dislocations accelerated formation of oxygen precipates and defect complex compounds are generated after three step annealing, which could be suction center of defect, that reduced carrier decentralized recombination centers that resulted in improvement of lifetime of wafer. Tendency of difference of lifetime was correlated with interior structure of crystalline silicon.

We have studied mechanisms of back-contact formation in screen-printed Si solar cells by a fire-through process. An optimum firing temperature profile leads to the formation of a P-Si/P+- Si/ Si-Al eutectic/agglomerated Al at the back contact of a Si solar cell. Variations in the interface properties were found to arise from Al-Si melt instabilities. Experiments were performed to study melt formation. We show that this process is strongly controlled by diffusion of Si into Al. During the ramp-up, a melt is initiated at the Si-Al interface, which subsequently expands into Al and Si. During the ramp-down, the melt freezes, which causes the doped region to grow epitaxially on Si, followed by solidification of the Si-Al eutectic. Any agglomerated (or sintered) Al particles are dispersed with Si. Implications on the performance of the cell are described.

We present an infrared spectroscopic ellipsometry investigation of SixNy films deposited on textured Si substrates employed for photovoltaic cells. A multiple-sample data analysis scheme is used in order to determine the SixNy dielectric function and thickness parameters regardless of the surface morphology of the substrate. We observe changes in the dielectric function of the silicon nitride film which suggest variations in the chemical composition of the films depending on the substrate morphology.

We report on our observations of light-activated passivation (LIP) of Si surfaces by iodine-ethanol (I-E) solution. Based on our experimental results, the mechanism of passivation appears to be related to dissociation of iodine by the photo-carriers injected from the Si wafer into the I-E solution. The ionized iodine (I−) then participates in the formation of a Si-ethoxylate bond that passivates the Si surface. Experiments with a large number of wafers of different material parameters indicate that under normal laboratory conditions, LIP can be observed only in some samples–samples that have moderate minority-carrier lifetime. We explain this observation and also show that wafer cleaning plays an extremely important role in passivation.