29 Matching Results

Search Results

Advanced search parameters have been applied.

in creator/contributor: "Ramanathan, K."

open access

Properties of High Efficiency CIGS Thin Film Solar Cells

We present experimental results in three areas. Solar cells with an efficiency of 19% have been fabricated with an absorber bandgap in the range of 1.1-1.2 eV. Properties of solar cells fabricated with and without an undoped ZnO layer were compared. The data show that high efficiency cells can be fabricated without using the high-resistivity or undoped ZnO layer. Properties of CIGS solar cells were fabricated from thin absorbers (1 {micro}m) deposited by the three-stage process and simultaneous… more

Date: February 1, 2005

Creator: Ramanathan, K.; Keane, J. & Noufi, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

AFM-Based Microelectrical Characterization of Grain Boundaries in Cu(In,Ga)Se2 Thin Films

We report on a direct measurement of two-dimensional potential distribution on the surface of Cu(In,Ga)Se2 thin films using a nanoscale electrical characterization of scanning Kelvin probe microscopy both in air and in ultra-high vacuum. The potential measurement reveals a higher surface potential or a smaller work function on grain boundaries (GBs) of the film than on the grain surfaces. This demonstrates the existence of a local built-in potential on GBs, and the GB is positively charged. The… more

Date: February 1, 2005

Creator: Jiang, C. S.; Noufi, R.; Ramanathan, K.; AbuShama, J. A.; Moutinho, H. R. & Al-Jassim, M. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Unusual Capacitance Emission Transients in CIGS Caused by Large Defect Entropy Changes

Capacitance transient data from bias-pulse experiments on CdS/CIGS solar cells show an unusual behavior at high temperatures. Above 350 K, a minority-carrier trap, with a larger activation energy than a majority-carrier trap, emits faster than the lower activation-energy minority trap. A simple enthalpy model for trap emission cannot explain this counterintuitive behavior; but the more complete Gibbs free-energy model that includes entropy can explain it. We show that entropy plays a major role… more

Date: February 1, 2005

Creator: Young, D. L.; Ramanathan, K. & Crandall, R. S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Optical Properties of Zn(O,S) Thin Films Deposited by RF Sputtering, Atomic Layer Deposition, and Chemical Bath Deposition: Preprint

Zn(O,S) thin films 27 - 100 nm thick were deposited on glass or Cu(InxGa1-x)Se2/Molybdenum/glass with RF sputtering, atomic layer deposition, and chemical bath deposition.

Date: June 1, 2012

Creator: Li, J.; Glynn, S.; Christensen, S.; Mann, J.; To, B.; Ramanathan, K. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Comparative Study of Zn(O,S) Buffer Layers and CIGS Solar Cells Fabricated by CBD, ALD, and Sputtering: Preprint

Zn(O,S) thin films were deposited by chemical bath deposition (CBD), atomic layer deposition, and sputtering. Composition of the films and band gap were measured and found to follow the trends described in the literature. CBD Zn(O,S) parameters were optimized and resulted in an 18.5% efficiency cell that did not require post annealing, light soaking, or an undoped ZnO layer. Promising results were obtained with sputtering. A 13% efficiency cell was obtained for a Zn(O,S) emitter layer deposited… more

Date: June 1, 2012

Creator: Ramanathan, K.; Mann, J.; Glynn, S.; Christensen, S.; Pankow, J.; Li, J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

CIGS Material and Device Stability: A Processing Perspective

This is a general overview of CIGS material and device fundamentals. In the first part, the basic features of high efficiency CIGS absorbers and devices are described. In the second part, some examples of previous collaboration with Shell Solar CIGSS graded absorbers and devices are shown to illustrate how process information was used to correct deviations and improve the performance and stability.

Date: March 1, 2012

Creator: Ramanathan, K.

Item Type: Presentation

Partner: UNT Libraries Government Documents Department

open access

Investigation of Cd1-XMgxTe Alloys for Tandem Solar Cell Applications: Preprint

Theoretical modeling of two-junction tandem solar cells shows that for optimal device performance, the bandgap of the top cell should be in the range of 1.6 to 1.8 eV. Cd1-xMgxTe (CMT) alloys have a lattice constant close to that of CdTe, and the addition of a small amount of Mg changes the bandgap considerably. In this paper, we present our work on developing CMT for solar cell applications. CMT films were prepared by vacuum deposition with co-evaporation of CdTe and Mg on substrates heated to… more

Date: May 1, 2006

Creator: Dhere, R.; Ramanathan, K.; Scharf, J.; Moutinho, H.; To, B.; Duda, A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Nondestructive Characterization of Atomic Profiles in Layer-Structured Photovoltaic Materials Using the Method of Angular Dependence of X-Ray Fluorescence (ADXRF)

Angular dependence of x-ray fluorescence technique has been applied to the study of atomic density profile in composite systems. This method is shown to be useful for probing the microstructures and intermixing of constituent elements in layer-structured photovoltaic materials.

Date: January 1, 2000

Creator: Kim, S.; Soo, Y. L.; Kioseoglou, G.; Huang, S.; Kao, Y. H.; Ramanathan, K. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Local Built-in Potential on Grain Boundary of Cu(In,Ga)Se2 Thin Films

We report on a direct measurement of two-dimensional potential distribution on the surface of Cu(In,Ga)Se2 (CIGS) thin films using a nanoscale electrical characterization of scanning Kelvin probe microscopy (SKPM). The potential measurement reveals a higher surface potential or a smaller work function on grain boundaries (GBs) of the film than on the grain surfaces. This demonstrates the existence of a local built-in potential on GBs and that the GB is positively charged. The role of the built-… more

Date: January 1, 2005

Creator: Jiang, C.-S.; Noufi, R.; Ramanathan, K.; AbuShama, J. A.; Moutinho, H. R. & Al-Jassim, M. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

CIGS Thin-Film Solar Cell Research at NREL: FY04 Results and Accomplishments

This short paper is a summary of our investigations in three major areas: high-efficiency CuInGaSe2 (CIGS) solar cells, junctions made using chemical bath deposited ZnS(O,OH) buffer layers, and solar cells fabricated from thinner absorbers. Significant progress was made in all areas. We describe how our research has contributed to the fundamental understanding and the practical application of CIGS materials to high performance solar cells.

Date: January 1, 2005

Creator: Ramanathan, K.; Bhattacharya, R. N.; Contreras, M. A.; Hasoon, F. S.; Abushama, J. & Noufi, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Fourier Transform Luminescence Spectroscopy of Semiconductor Thin Films and Devices

We have been successful in adapting Fourier transform (FT) Raman accessories and spectrophotometers for sensitive measurements of the photoluminescence (PL) spectra of photovoltaic materials and devices. In many cases, the sensitivity of the FT technique allows rapid room-temperature measurements of weak luminescence spectra that cannot be observed using dispersive PL spectrophotometers. We present here the results of a number of studies of material and device quality obtained using FT-luminesc… more

Date: July 12, 1999

Creator: Webb, J. D.; Keyes, B. M.; Ahrenkiel, R. K.; Wanlass, M. W.; Ramanathan, K.; Gedvilas, L. M. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Junction Formation in CuInSe{sub 2} Based Thin Film Devices

The nature of the interface between CuInSe{sub 2} (CIS) and the chemical bath deposited CdS layer has been investigated. We show that heat-treating the absorbers in Cd- or Zn-containing solutions in the presence of ammonium hydroxide sets up a chemical reaction which facilitates an extraction of Cu from the lattice and an in-diffusion of Cd. The characteristics of devices made in this manner suggest that the reaction generates a thin, n-doped region in the absorber. It is quite possible that th… more

Date: November 18, 1998

Creator: Ramanathan, K.; Wiesner, H.; Asher, S.; Bhattacharya, R. N.; Keane, J.; Contreras, M. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Barrier to Trap Filling CuIn1-xGaxSe2: Preprint

Voltage pulses of variable length were applied to CuIn1-xGaxSe2/CdS (0< x< 1) junction solar cells. The resulting transient capacitance emission signal was recorded for several minutes. The amplitude of the capacitance emission signal increased linearly with the log of pulse time. These data do not follow the standard model for trap capture and emission of carriers. Instead they follow a simple electrostatic model based on electrostatic charging of traps.

Date: April 1, 2003

Creator: Young, D. L.; Ramanathan, K.; Contreras, M.; Abushama, J. & Crandall, R. S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Mesoscopic Fluctuations in the Distribution of Electronic Defects Near the Surface Layer of Cu(In,Ga)Se2

High-resolution cathodoluminescence spectroscopic imaging (CLSI) has been employed to study the radiative recombination processes in Cu(In,Ga)Se2 (CIGS) films used in solar cells. Mesoscopic fluctuations of the electrostatic potential explain the observed behavior for the radiative transitions identified in the emission spectrum. We show evidence for passivation of grain boundaries near the surface layers of these films. In addition, our results suggest different point defect physics for the su… more

Date: May 1, 2003

Creator: Romero, M. J.; Ramanathan, K.; Contreras, M. A.; Al-Jassim, M. M.; AbuShama, J. & Noufi, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Investigation of the Microstructure of Cu(In,Ga)Se2 Thin Films Used in High-Efficiency Devices: Preprint

This conference paper describes the microstructure of Cu(In,Ga)Se2 (CIGS) films, as it transitioned from Cu-rich to In-rich composition, by transmission electron microscopy, and energy-dispersive X-ray spectroscopy. We find that the Cu-rich samples have larger grains than the In-rich samples, and they contain two structurally different forms of the CuxSe secondary phase. These samples also show sub-interfaces about 0.2 ..mu..m below the surface. The In-rich samples were almost void of these sub… more

Date: May 1, 2002

Creator: Noufi, R.; Yan, Y.; Abu-Shama, J.; Jones, K.; Al-Jassim, M.; Keyes, B. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Electrodeposition of CuIn1-xGaxSe2 Materials for Solar Cells:

This report describes our scientific understanding of the CIGS materials system, solar cells, and processes. Through DOE support, the investigators developed much of the technology and device fabrication infrastructure applied to electrodeposited (ED) materials. The electrodeposition process is simple and fast, and can synthesize multinary precursors for subsequent processing into CuInxGa1-xSe2 (CIGS) thin-film absorbers for solar cells. The device fabricated by using electrodeposited CIGS prec… more

Date: October 1, 2002

Creator: Bhattacharya, R. N.; Fernandez, A. M.; Batchelor, W.; Alleman, J.; Keane, J.; Althani, H. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Surface Treatment of CuInGaSe2 Thin Films and Its Effect on the Photovoltaic Properties of Solar Cells: Preprint

Solar cells have been fabricated with partial electrolyte treatments of CuInGaSe2 (CIGS) thin-film absorbers in lieu of a CdS layer. Treatment of the absorbers in a containing Cd or Zn solution is shown to produce conditions under which efficient solar cells can be fabricated. A similar effect is also observed in CuInGaSSe2 (CIGSS) graded-bandgap absorbers. These observations can be explained by the ability of Cd and Zn to produce n-type doping or inversion in the surface region. We also provid… more

Date: October 1, 2002

Creator: Ramanathan, K.; Hasoon, F. S.; Smith, S.; Young, D. L.; Contreras, M. A.; Johnson, P. K. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Mapping Capabilities of the FTIR Laboratory and Support of the Combinatorial Growth Efforts: Preprint

Presented at the 2001 NCPV Program Review Meeting: The FTIR Spectroscopy Laboratory has enhanced its support of the PV Program through the incorporation automated mapping capabilities.

Date: October 1, 2001

Creator: Keyes, B. M.; Gedvilas, L. M.; Perkins, J. D.; Ginley, D. S.; del Cueto, J.; Ramanathan, K. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Nano-scale Optical Spectroscopy of PV Materials: Preprint

Presented at the 2001 NCPV Program Review Meeting: Micro-PL, solid immersion lens microscopy, and near-field microscopy characterized the low-temperature PL of PV materials and devices with sub-micron spatial resolution. A variety of novel high-spatial resolution techniques, including micro-PL, solid immersion lens microscopy and near-field microscopy have been used to characterize the low-temperature photoluminescence of photovoltaic materials and devices with sub-micron spatial resolution. Th… more

Date: October 1, 2001

Creator: Smith, S.; Dhere, R.; Ramanathan, K. & Mascarenhas, A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Effect of Na Incorporation on the Growth and Properties of CdTe/CdS Devices OF CdTe/CdS DEVICES

Sodium is known to enhance p-type doping in copper indium diselenide (CIS)-based devices fabricated on soda-lime glass substrates, and similar amounts of Na are present in commercial cadmium telluride (CdTe) devices. We present the results on the effects of Na incorporation on the properties of CdTe/CdS solar cells prepared on borosilicate glass substrates. A NaF layer 10 to 30 nm thick was incorporated at either the CdS/CdTe interface or on the CdTe surface, as a source of Na. CdTe layers were… more

Date: February 1, 2005

Creator: Dhere, R.; Ramanathan, K.; Keane, J.; Zhou, J.; Moutinho, H.; Asher, S. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Properties of Cd and Zn Partial Electrolyte Treated CIGS Solar Cells: Preprint

We study the influence of Cd partial baths on the photovoltaic properties of CuInGaSe2 (CIGS) and CuIn-GaSSe2 (CIGSS) thin film absorbers. We find that efficient solar cells can be fabricated by this treatment, and we compare their properties with those containing CdS window layers grown by chemical bath deposition. The results suggest that Cd plays a dominant role in establishing efficient photovoltaic junctions in CuInSe2 alloys. Micron scale photoluminescence scans show non-uniformity along … more

Date: May 1, 2002

Creator: Ramanathan, K.; Hasoon, F. S.; Smith, S.; Mascarenhas, A.; Al-Thani, H.; Alleman, J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Recent Progress in CIGS Thin Film Solar Cell Research at NREL: Preprint

Presented at the 2001 NCPV Program Review Meeting: This paper summarizes our work toward improving reproducibility in fabricating high efficiency absorbers and devices. This paper summarizes our work toward improving reproducibility in fabricating high efficiency absorbers and devices. This resulted in the fabrication of a CIGS cell with an efficiency of 21% under concentrated light. We compare devices fabricated with CdS and with Cd solution treatment alone. A high conversion efficiency of 15.… more

Date: October 1, 2001

Creator: Ramanathan, K.; Hasoon, F. S.; Al-Thani, H.; Alleman, J.; Keane, J.; Dolan, J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Cu(In,Ga)Se2 Thin-Film Concentrator Solar Cells: Preprint

Presented at the 2001 NCPV Program Review Meeting: CIGS cells were designed for operation under concentrated sunlight. This is first report of polycrystalline thin-film cell with efficiency>20%.

Date: October 1, 2001

Creator: Ward, J.; Ramanathan, K.; Hasoon, F.; Coutts, T.; Keane, J.; Moriarty, T et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Investigation of Cd1-xMgxTe Alloys for Tandem Solar Cell Applications (Poster)

Fabrication and characterization of Cd{sub 1-x}Mg{sub x}Te(CMT) alloys and to determine their potential for device applications. Main emphasis is on the development of the devices in 1.5 to 1.8 eV range for the top cell of two-junction tandem solar cells. The conclusions are: (1) CMT alloy films with a wide composition range were fabricated; (2) the optical band gap shows a systematic variation with composition and CMT alloy films withstood the commonly used device processing steps for CdTe; an… more

Date: May 1, 2006

Creator: Dhere, R.; Ramanathan, K.; Scharf, J.; Moutinho, H.; To, B.; Duda, A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department