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Full-Text Articles in Physics

Electron And Hole Drift Mobility Measurements On Thin Film Cdte Solar Cells, Qi Long, Steluta A. Dinca, Eric A. Schiff, Ming Yu, Jeremy Theil Jul 2014

Electron And Hole Drift Mobility Measurements On Thin Film Cdte Solar Cells, Qi Long, Steluta A. Dinca, Eric A. Schiff, Ming Yu, Jeremy Theil

Physics

We report electron and hole drift mobilities in thin film polycrystalline CdTe solar cells based on photocarrier time-of-flight measurements. For a deposition process similar to that used for high-efficiency cells, the electron drift mobilities are in the range of 10–100 cm2/Vs, and holes are in the range of 1–10 cm2/Vs. The electron drift mobilities are about a thousand times smaller than those measured in single crystal CdTe with time-of-flight; the hole mobilities are about ten times smaller. Cells were examined before and after a vapor phase treatment with CdCl2; treatment had little effect ...


Electron Drift-Mobility Measurements In Polycrystalline Cuin1-Xgaxse2 Solar Cells, Steluta A. Dinca, Eric A. Schiff, William N. Shafarman, Brian Egaas, Rommel Noufi, David L. Young Mar 2012

Electron Drift-Mobility Measurements In Polycrystalline Cuin1-Xgaxse2 Solar Cells, Steluta A. Dinca, Eric A. Schiff, William N. Shafarman, Brian Egaas, Rommel Noufi, David L. Young

Physics

We report photocarrier time-of-flight measurements of electron drift mobilities for the p-type CuIn1-xGaxSe2 films incorporated in solar cells. The electron mobilities range from 0.02 to 0.05 cm^2/Vs and are weakly temperature-dependent from 100–300 K. These values are lower than the range of electron Hall mobilities (2-1100 cm2/Vs) reported for n-type polycrystalline thin films and single crystals. We propose that the electron drift mobilities are properties of disorder-induced mobility edges and discuss how this disorder could increase cell efficiencies.


Thermodynamic Limit To Photonic-Plasmonic Light-Trapping In Thin Films On Metals, Eric A. Schiff Nov 2011

Thermodynamic Limit To Photonic-Plasmonic Light-Trapping In Thin Films On Metals, Eric A. Schiff

Physics

We calculate the maximum optical absorptance enhancements in thin semiconductor films on metals due to structures that diffuse light and couple it to surface plasmon polaritons. The calculations can be used to estimate plasmonic effects on light-trapping in solar cells. The calculations are based on the statistical distribution of energy in the electromagnetic modes of the structure, which include surface plasmon polariton modes at the metal interface as well as the trapped waveguide modes in the film. The enhancement has the form 4n2+/h (n – film refractive index, λ – optical wavelength, h – film thickness), which is an ...


Polyaniline On Crystalline Silicon Heterojunction Solar Cells, Weining Wang, Eric A. Schiff Jan 2007

Polyaniline On Crystalline Silicon Heterojunction Solar Cells, Weining Wang, Eric A. Schiff

Physics

Organic/inorganic heterojunction solar cells were fabricated on the (100) face of n-type silicon crystals using acid-doped polyaniline PANI with widely varying conductivities. For films with conductivities below 10−1 S/cm, the open-circuit voltage VOC increases with increasing film conductivity as expected when VOC is limited by the work function of the film. Extrapolation of these results to the higher conductivity films indicates that PANI could support VOC of 0.7 V or larger. VOC measurements for the cells with higher conductivity PANI saturated at 0.51 V. We speculate that uncontrolled surface states at the PANI/Si interface ...


Hole Mobilities And The Physics Of Amorphous Silicon Solar Cells, Eric A. Schiff Jan 2006

Hole Mobilities And The Physics Of Amorphous Silicon Solar Cells, Eric A. Schiff

Physics

The effects of low hole mobilities in the intrinsic layer of pin solar cells are illustrated using general computer modeling; in these models electron mobilities are assumed to be much larger than hole values. The models reveal that a low hole mobility can be the most important photocarrier transport parameter in determining the output power of the cell, and that the effects of recombination parameters are much weaker. Recent hole drift-mobility measurements in a-Si:H are compared. While hole drift mobilities in intrinsic a-Si:H are now up to tenfold larger than two decades ago, even with recent materials a-Si ...


Hole Mobility Limit Of Amorphous Silicon Solar Cells, Jiang Liang, Eric A. Schiff, S. Guha, Baojie Yan, Jeff Yang Jan 2006

Hole Mobility Limit Of Amorphous Silicon Solar Cells, Jiang Liang, Eric A. Schiff, S. Guha, Baojie Yan, Jeff Yang

Physics

We present temperature-dependent measurements and modeling for a thickness series of hydrogenated amorphous silicon nip solar cells. The comparison indicates that the maximum power density (PMAX) from the as-deposited cells has achieved the hole-mobility limit established by valence bandtail trapping, and PMAX is thus not significantly limited by intrinsic-layer dangling bonds or by the doped layers and interfaces. Measurements of the temperature-dependent properties of light-soaked cells show that the properties of as-deposited and light-soaked cells converge below 250 K; a model perturbing the valence band tail traps with a density of dangling bonds accounts adequately for the convergence effect.


Light-Soaking Effects On The Open-Circuit Voltage Of A-Si:H Solar Cells, Jianjun Liang, Eric A. Schiff, S. Guha, Baojie Yan, J. Yang Jan 2005

Light-Soaking Effects On The Open-Circuit Voltage Of A-Si:H Solar Cells, Jianjun Liang, Eric A. Schiff, S. Guha, Baojie Yan, J. Yang

Physics

We present measurements on the decline of the open-circuit voltage VOC in a-Si:H solar cells during extended illumination (light-soaking) at 295 K. We used a near-infrared laser that was nearly uniformly absorbed in the intrinsic layer of the cell. At the highest photogeneration rate (about 2x1021 cm-3), a noticeable decline (0.01 V) occurred within about 10 minutes; VOC stabilized at 0.04 V below its initial value after about 200 hours. We found that both the kinetics and the magnitudes of VOC are reasonably consistent with the predictions of a calculation combining a bandtail+defect picture for recombination ...


Conducting Polymer And Hydrogenated Amorphous Silicon Hybrid Solar Cells, Evan L. Williams, Ghassan E. Jabbour, Qi Wang, Sean E. Shaheen, Eric A. Schiff Jan 2005

Conducting Polymer And Hydrogenated Amorphous Silicon Hybrid Solar Cells, Evan L. Williams, Ghassan E. Jabbour, Qi Wang, Sean E. Shaheen, Eric A. Schiff

Physics

An organic-inorganic hybrid solar cell with a p-i-n stack structure has been investigated. The p-layer was a spin coated film of PEDOT:PSS poly 3,4-ethylenedioxythiophene polystyrenesulfonate. The i-layer was hydrogenated amorphous silicon a-Si:H, and the n-layer was microcrystalline silicon c-Si. The inorganic layers were deposited on top of the organic layer by the hot-wire chemical vapor deposition technique at 200 °C. These hybrid devices exhibited open circuit voltages VOC as large as 0.88 V and solar conversion efficiencies as large as 2.1%. Comparison of these devices with those incorporating a-SiC:H:B p-layers indicates that the ...


Temperature-Dependent Open-Circuit Voltage Measurements And Light-Soaking In Hydrogenated Amorphous Silcon Solar Cells, Jianjun Liang, Eric A. Schiff, S. Guha, Baojie Yan, Jeff Yang Jan 2005

Temperature-Dependent Open-Circuit Voltage Measurements And Light-Soaking In Hydrogenated Amorphous Silcon Solar Cells, Jianjun Liang, Eric A. Schiff, S. Guha, Baojie Yan, Jeff Yang

Physics

We present temperature-dependent measurements of the open-circuit voltage VOC(T) in hydrogenated amorphous silicon nip solar cells prepared at United Solar. At room-temperature and above, VOC measured using near-solar illumination intensity differs by as much as 0.04 V for the as-deposited and light-soaked states; the values of VOC for the two states converge below 250 K. Models for VOC based entirely on recombination through deep levels (dangling bonds) do not account for the convergence effect. The convergence is present in a model that assumes the recombination traffic in the as-deposited state involves only bandtails, but which splits the recombination ...


Amorphous Silicon Based Solar Cells, Xunming Deng, Eric A. Schiff Jan 2003

Amorphous Silicon Based Solar Cells, Xunming Deng, Eric A. Schiff

Physics

Crystalline semiconductors are very well known, including silicon (the basis of the integrated circuits used in modern electronics), Ge (the material of the first transistor), GaAs and the other III-V compounds (the basis for many light emitters), and CdS (often used as a light sensor). In crystals, the atoms are arranged in near-perfect, regular arrays or lattices. Of course, the lattice must be consistent with the underlying chemical bonding properties of the atoms. For example, a silicon atom forms four covalent bonds to neighboring atoms arranged symmetrically about it. This “tetrahedral” configuration is perfectly maintained in the “diamond” lattice of ...


Bandtail Limits To Solar Conversion Efficiencies In Amorphous Silicon Solar Cells, Kai Zhu, Weining Wang, Eric A. Schiff, Jianjun Liang, S. Guha Jan 2003

Bandtail Limits To Solar Conversion Efficiencies In Amorphous Silicon Solar Cells, Kai Zhu, Weining Wang, Eric A. Schiff, Jianjun Liang, S. Guha

Physics

We describe a model for a-Si:H based pin solar cells derived primarily from valence bandtail properties. We show how hole drift-mobility measurements and measurements of the temperature-dependence of the open-circuit voltage VOC can be used to estimate the parameters, and we present VOC(T) measurements. We compared the power density under solar illumination calculated with this model with published results for as-deposited a-Si:H solar cells. The agreement is within 4% for a range of thicknesses, suggesting that the power from as-deposited cells is close to the bandtail limit.


Thermionic Emission Model For Interface Effects On The Open-Circuit Voltage Of Amorphous Silicon Based Solar Cells, Eric A. Schiff Jan 2002

Thermionic Emission Model For Interface Effects On The Open-Circuit Voltage Of Amorphous Silicon Based Solar Cells, Eric A. Schiff

Physics

We present computer modeling for effects of the p/i interface upon the open-circuit voltage VOC in amorphous silicon based pin solar cells. We show that the modeling is consistent with measurements on the intensitydependence for the interface effect, and we present an interpretation for the modeling based on thermionic emission of electrons over the electrostatic barrier at the p/i interface. We present additional modeling of the relation of VOC with the intrinsic layer bandgap EG. The experimental correlation for optimized cells is VOC = (EG/e)-0.79. The correlation is simply explained if VOC in these cells is ...


Determining The Locus For Photocarrier Recombination In Dye-Sensitized Solar Cells, Kai Zhu, Eric A. Schiff, N. G. Park, J. Van De Lagemaat, A. J. Frank Jan 2002

Determining The Locus For Photocarrier Recombination In Dye-Sensitized Solar Cells, Kai Zhu, Eric A. Schiff, N. G. Park, J. Van De Lagemaat, A. J. Frank

Physics

We present intensity-modulated photocurrent and infrared transmittance measurements on dye-sensitized solar cells based on a mesoporous titania (TiO2) matrix immersed in an iodine-based electrolyte. Under short-circuit conditions, we show that an elementary analysis accurately relates the two measurements. Under open-circuit conditions, infrared transmittance, and photovoltage measurements yield information on the characteristic depth at which electrons recombine with ions (the ‘‘locus of recombination’’). For one particular series of samples recombination occurred near the substrate supporting the titania film, as opposed to homogeneously throughout the film.