Transparent conductors—A status review

Energy harvesting generators are attractive as inexhaustible replacements for batteries in low-power wireless electronic devices and have received increasing research interest in recent years. Ambient motion is one of the main sources of energy for harvesting, and a wide range of motion-powered energy harvesters have been proposed or demonstrated, particularly at the microscale. This paper reviews the principles and state-of-art in motion-driven miniature energy harvesters and discusses trends, suitable applications, and possible future developments.

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Energy Harvesting From Human and Machine Motion for Wireless Electronic Devices

This Review focuses on recent developments in the use of ZnO nanostructures for dye-sensitized solar cell (DSC) applications. It is shown that carefully designed and fabricated nanostructured ZnO films are advantageous for use as a DSC photoelectrode as they offer larger surface areas than bulk film material, direct electron pathways, or effective light-scattering centers, and, when combined with TiO2, produce a core–shell structure that reduces the combination rate. The limitations of ZnO-based DSCs are also discussed and several possible methods are proposed so as to expand the knowledge of ZnO to TiO2, motivating further improvement in the power-conversion efficiency of DSCs.

https://depts.washington.edu/solgel/documents/pub_docs/journal_docs/2009/advanced_material2009.pdf

ZnO Nanostructures for Dye-Sensitized Solar Cells

http://nathan.instras.com/documentDB/paper-44.pdf

Surface photovoltage phenomena: theory, experiment, and applications

To convert the energy of sunlight into chemical energy, the leaf splits water via the photosynthetic process to produce molecular oxygen and hydrogen, which is in a form of separated protons and electrons. The primary steps of natural photosynthesis involve the absorption of sunlight and its conversion into spatially separated electron–hole pairs. The holes of this wireless current are captured by the oxygen evolving complex (OEC) of photosystem II (PSII) to oxidize water to oxygen. The electrons and protons produced as a byproduct of the OEC reaction are captured by ferrodoxin of photosystem I. With the aid of ferrodoxin–NADP+ reductase, they are used to produce hydrogen in the form of NADPH. For a synthetic material to realize the solar energy conversion function of the leaf, the light-absorbing material must capture a solar photon to generate a wireless current that is harnessed by catalysts, which drive the four electron/hole fuel-forming water-splitting reaction under benign conditions and under 1 su...

The artificial leaf

Cast multicrystalline silicon (mc-Si) shows a significant variation in quality depending on the location of the brick in the ingot and the location of the wafer in the brick. Variation also occurs in ingots from different suppliers, which is attributed to the difference in the cleanliness of the crucible used for growth and the quality of the silicon feedstock used. Process-induced lifetime investigation conducted in this paper showed that wafers from the top region of mc-Si ingot grown by Heat Exchanger Method (HEM) benefited most from the gettering step during phosphorus diffusion to form the n + junction. Wafers from the bottom of the ingot, however, benefited most from the hydrogenation taking place from the SiN x film during the co-firing cycle used to form simultaneous front and back contacts and aluminum back surface field. Wafers from the middle region benefited from both, the diffusion-gettering, and the SiN x -hydrogenation. Un-textured, 4 cm 2 , screen-printed, best solar cell efficiencies of 15.9% and above were achieved on wafers from top, middle, and bottom regions of most of the ingots used in this study because the bulk lifetime exceeded 100 μs after gettering and hydrogenation. Lifetimes in excess of 300 μs were achieved from the middle region of some mc-Si ingots. Solar cell efficiencies of 16.7% were attained from the middle regions of two out of the three ingots investigated in this study. Device modeling was performed to provide guidelines to reduce the efficiency variation across different regions of the ingots and to obtain the highest possible efficiency with a given bulk lifetime and device structure.

Bulk lifetime and efficiency enhancement due to gettering and hydrogenation of defects during cast multicrystalline silicon solar cell fabrication

Summary form only given. The radial distribution feeder protection strategy is first presented in the paper without consideration for DG. Then, the addition of DG across the feeder (constrained in terms of power and/or energy capacity) is introduced in the model. If islanded operation of these DG sources is allowed on a feeder subjected to a disturbance, DG may reduce the number of interruptions and/or durations for customers residing within their protection zones, thus increasing the reliability of service. To that end, a procedure for finding optimal positions for DG and protection devices is presented for a feeder equipped with capacity-constrained distributed generators, using a custom-tailored genetic algorithm, and the improvement in reliability is demonstrated on a test feeder. Tuning of the genetic algorithm parameters, and an adaptive algorithm that eliminates the need for parameter tuning are the subject of a separate paper by the same authors.

Recloser Allocation for Improved Reliability of DG-Enhanced Distribution Networks

A high voltage hydrogenated amorphous silicon (a-Si:H) solar cell array which is optimized as a power source for electrostatic microelectromechanical systems (MEMS) is presented. A single test cell consists of a triple stack of p-i-n/p-i-n/p-i-n material and produces open circuit voltage (OCV) of 1.8/spl sim/2.3 volts, short circuit current density (J/sub sc/) of 2.8 mA/cm/sup 2/, and fill factor (FF) of 0.495. A series interconnected array of 100 of these cells (total array area of 1 cm/sup 2/) has been produced in an integrated fashion and produces an array OCV of 150 volts, and short circuit current (I/sub SC/) of 2.8 /spl mu/A under Air Mass (AM) 1.5 illumination. To illustrate the use of this array as a MEMS power source, it has been packaged with a movable micromachined silicon (Si) mirror in a hybrid manner. The movable Si mirror is directly driven by the cell array electrical output, and the motion of the mirror plate has been observed reproducibly. Variation of light intensity and/or number of illuminated cells produces different array OCVs, thus enabling control of the deflection of the Si mirror by variation of incident light.

High voltage solar cell array as an electrostatic MEMS power supply

Thin hydrogenated amorphous silicon (a-Si:H) layers deposited by hot-wire chemical vapor deposition (HWCVD) are investigated for use in silicon heterojunction (SHJ) solar cells on p-type crystalline silicon wafers. A requirement for excellent emitter quality is minimization of interface recombination. Best results necessitate immediate a-Si:H deposition and an abrupt and flat interface to the c-Si substrate. We obtain a record planar HJ efficiency of 16.9% with a high V/sub oc/ of 652 mV on p-type float-zone (FZ) silicon substrates with HWCVD a-Si:H(n) emitters and screen-printed Al-BSF contacts. H pretreatment by HWCVD is beneficial when limited to a very short period prior to emitter deposition.

/pdf/effective-interfaces-in-silicon-heterojunction-solar-cells-ugbxh6n5ml.pdf

Effective interfaces in silicon heterojunction solar cells

Increased interest in light-trapping techniques to enhance the output current of silicon solar cells has led to a variety of surface texturing designs. Unfortunately, the inability to quantify and eliminate some of the photon loss mechanisms have not allowed textured cells to reach their full potential. Texture, a Monte Carlo ray-tracing program which is capable of addressing the above issues, has been written. The program has a convenient user interface and a variety of output modes. Different material systems, such as GaAs, InP, and thin films on textured glass, can also be modeled by Texture. It is shown that the output of the Texture program compares quite favorably with results of other researchers under the same assumptions. The program also provides additional quantitative information about photon losses due to the sides of the cell, grid absorption, and imperfect back-surface reflectance. Output results show that tetrahedrons are more effective light-trapping structures than tilted pyramids (40.87 mA compared to 40.37 mA). >

Ajeet Rohatgi

Papers

Bulk lifetime and efficiency enhancement due to gettering and hydrogenation of defects during cast multicrystalline silicon solar cell fabrication

Recloser Allocation for Improved Reliability of DG-Enhanced Distribution Networks

High voltage solar cell array as an electrostatic MEMS power supply

Effective interfaces in silicon heterojunction solar cells

Texture: a ray tracing program for the photovoltaic community