Photovoltaic materials and device research gas number


MRC scientists and students have established a world-class laboratory for research in photovoltaic(solar) energy conversion materials and devices. The program focuses on growth of thin film electronic materials suitable for photovoltaic conversion, and on fabricating devices in them. Current materials of interest include amorphous Si and its alloys, and CdTe.

A-Si is deposited using a remote, reactive ECR plasma deposition, and after deposition, the films are characterized for their optical and electronic properties. The reactors gas south can be used also to make doped layers and devices in these films. The devices are measured using solar simulators and other electronic measurement techniques, such as capacitance-frequency measurements and quantum efficiency measurements. This is an active research program, supported by National Renewable Energy Laboratory and by industry. ISU is one of the leaders in the world in this field.

Another part of the a-Si program is a theoretical effort to understand the microscopic origins of defects in a-Si, using molecular dynamic simulations to simulate local Si-Si and Si-H p gasket 300tdi bonds in the material, and their statistical distributions. The simulations also try to model the movement of H in these materials in response to energetic inputs, and see how these movements and bond-rearrangements affect the electronic properties.

This theoretical effort is complemented by experimental work to measure the diffusion of H and D in a-Si , a-(Si,C) and a-(Si,Ge) materials. It is known that diffusion of H plays a critical role in defect creation in these materials, and by using Secondary Ion Mass Spectroscopy, one can determine the diffusion kinetics of H and D, and correlate them with the defect structure in the material.

B. Semiconductor Process research Production cost of solar electric conversion panels is the critical element which determines grade 9 electricity test and answers their commercial success. We work with a local company, Iowa Thin Film technologies, Inc.(ITFT), which is a spin-off from ISU, to improve the processing of solar cells. ITFT deposits these cells on polyimide substrates, in continuous deposition reactors using a roll-to-roll process. ISU scientists work gas station car wash with ITFT to understand the plasma processes that govern deposition, and on development of in-situ sensors for process controls and reliability.

New applications, such as large area conformal displays, conformal electronic devices for biological applications, driver circuits for organic LED’s etc. require that high quality electronic devices be made on insulating substrates, sometimes even on plastic substrates. MRC scientists and students have developed several new technologies for depositing both amorphous and crystalline Si devices on plastic substrates. Using a rective ECR plasma beam process, we have been able to deposit thin films of crystalline Si directly on a plastic substrate without having electricity vocabulary words to do any laser recrystallization. Recently, we produced a crystalline Si solar cell on polyimide substrates with very good properties. This development is likely to revolutionize semiconductor technology by allowing for multiple-device integration on insulating layers.

Nanocrystalline Si:H is a fascinating new electronic material. The Si grains are small, ~10-20 nm, and the grain-boundaries are coated with H and very thin a-Si:H. The H distribution in the material can be estimated using Molecular Dynamic simulations, and is shown in Fig. 1. The simulations clearly show that most of the hydrogen is at the grain boundaries, with nothing inside the nano-grain. The presence of H and a-Si:H tissue at the grain boundaries passivates these boundaries, and allows for efficient transfer 101 gas station of minority and majority carriers across the grain. As a result, hole lifetimes of the order of microsecond can be obtained even in this nanocrystallione material. Electron mobilities are of the order of 30 cm 2/V-sec and hole mobilities ~ 10 cm 2/V-sec in as-grown materials, orders of magnitude higher than in amorphous materials. The hole diffusion lengths can be in excess of 1 micrometer. See Fig. 2. The nanocrystalline Si material is fundamentally stable, as opposed to amorphous materials. These outstanding properties allow one to make useful devices like solar cells and thin film transistors on plastic substrates in this material.

Spectroscopic gas sensors have greater sensitivity and stability than conventional electrochemical sensors. Spectroscopic sensors of toxic gases rely on the fact that each grade 6 electricity quiz gas has a unique absorption line in the infrared portion of the spectrum, arising from the molecular stretching or rotational modes. For example CO has a sharp absorption at 4.7 m, NO absorbs at 5.3 m whereas nerve gases and toxic serin have absorption features near 10 m. Spectroscopic infrared gas sensors offer very high sensitivity for conclusive detection of individual species since each gas has unique absorption lines in the infrared spectrum. Spectroscopic sensors are lightweight, battery-powered, low-maintenance and low-cost- essential attributes for counter-terrorism applications.

This has been a long standing project simulating nanocrystalline and amorphous silicon thin films. The objective of the research is to identify, explore, evaluate and model new heterogeneous thin film materials capable of making a breakthrough in the production of low cost electricity from sunlight. This project has gas 0095 download been part of the NREL national thin film solar cell team effort.

The Staebler-Wronski effect or the degradation of thin film silicon solar cells when they are placed in sunlight is a mystery that has plagued the research community for more than 20 years. When such solar cells are kept in sunlight their efficiency drops by 15-20% over a period of several days. Intensive studies have established that these changes are due to creating of mid-gap defect states from silicon dangling bonds in the amorphous silicon films. From an annealed defect density of 10 15 cm -3, the defect density rises to 10 16-10 17 cm -3 after light-soaking. The metastable changes are reversible and can be removed by annealing the material at 180-200 C. The metastable electricity and magnetism worksheets defects are indistinguishable from native dangling bond defects. Significantly the metastable defects are at least 4 Å distant from hydrogen sites- indicating an anti-correlation with H.

We proposed a new mechanism explaining many features electricity online games of the Staebler-Wronski effect [1,2]. In the first step sunlight creates an excess density of electrons and holes. The electrons recombine with holes on weak silicon bonds in the material. The recombination energy causes the weak silicon bonds to break, generating silicon dangling bond – floating bond pairs. Accurate tight-binding molecular dynamics simulations have established the lowering oif energy barriers for bond-breaking when excited e-h pairs are present. During the second step, the floating bonds (over-coordinated silicon atoms) diffuse away from the dangling bonds and move freely throughout the material since they are electricity rate per kwh philippines a mobile species. In the third step the floating bonds recombine with themselves or with H in the network, and the network is left with primarily dangling bonds. An interesting caveat is that because of charge neutrality charged dangling bond defects are formed in addition to the neutral species. Many features of the Staebler-Wronski are explained well by this model ( Phys. Rev. Lett. paper, book chapter). The model has been featured in news releases ( Ames Lab Inquiry article, Hindu).

Nanocrystalline silicon was simulated consisting of nanocrystallites embedded in an amorphous matrix. The presence of the nanocrystallite improves the ordering of the amorphous matrix which may account for the higher stability electricity generation capacity of nanocrystalline silicon towards light soaking. The nanoscale structure can inhibit the instability and breaking of weak bonds.

There is a thin disordered region around the nanocrystal containing an excess density of H where the H density is about twice the background H density. By performing simulations at various temperatures and monitoring the motion of H, we found that the excess grain boundary H is responsible for the anomalous low-temperature H evolution peak that occurs near 400C in addition to the high temperature H evolution peak at 600C.