bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sub-micron Optoelectronic Properties of Polycrystalline Solar Cell Materials
Authors: Smith S. , Dhere R. , Gessert T. , Stradins P. , Wang T. , Ramanathan K. , Noufi R. , Mascarenhas A. 
Published: November 2011

AbstractGeneration, transport and collection of carriers in polycrystalline (PX) solar cells and their constituent materials are poorly understood, and significantly different than in their single-crystal counterparts. Recent theoretical and experimental results have put forth the expectation that grain boundaries in PX-solar cell materials such as CdTe and CuInGaSe2, either as-grown or after appropriate post-growth treatment, may have electronic properties which are advantageous to charge separation and solar cell operation[1-3]. However, a microscopic picture of the spatial variations in the optoelectronic properties of these materials is, for the most part, still lacking. The goal of the work reported here is to explore the optoelectronic and spectroscopic properties of grain-boundaries in these materials at the nanometer length-scale, via novel, high-resolution optical techniques. Towards this end, a significant enhancement in photo-response near grain boundaries in CdTe solar cells, consistent with models put forth in reference 2, was observed via near-field Optical Beam Induced Current (n-OBIC) [4]. A systematic μ-PL study of the effect of CdC12-treatment on recombination in CdTe/CdS solar cell structures of varying thickness directly examined the variation in optoelectronic properties at grain-boundaries in this material, revealing the grain-boundary and surface passivation effects of this important post-growth processing step. For comparison, we also studied the effects of SiNx post-growth treatment and annealing on the photo-response of PX-silicon solar cells using n-OBIC. These results and our most-recent n-OBIC measurements in CdTe and CuInGaSe2 solar cells are discussed.
Solar Cells prepared with Spray-ILGAR Indium Sulfide buffer layers on Cu(In,Ga)Se2 Absorbers
Authors: Allsop Nicholas A. , Kaufmann Christian A. , Neisser Axel , Rusu Marin , Hänsel Andreas , Lux-Steiner Martha C. , Fischer Christian H. 
Published: November 2011

AbstractIndium sulfide buffer layers deposited by the Spray-Ion Layer Gas Reaction (Spray-ILGAR) technique have recently been used with Cu(In,Ga)(S,Se)2 absorbers giving cells with an efficiency equal to the cadmium sulfide references. In this paper we show the first results from cells prepared with Cu(In,Ga)Se2 absorbers (sulfur free). These cells reach an efficiency of 13.1% which remains slightly below the efficiency of the cadmium sulfide reference. However, temperature dependant current-voltage measurements reveal that the activation energy of the dominant recombination mechanism remains unchanged from the cadmium sulfide buffered cells indicating that recombination remains within the space charge region.
Growth of CuInSe2 monograin powders with different compositions
Authors: Kauk Marit , Altosaar Mare , Raudoja Jaan , Timmo Kristi , Grossberg Maarja , Varema Tiit , Mellikov Enn 
Published: November 2011

AbstractCuInSe2 monograin powders (MGP) were synthesized from Cu-In alloys of different Cu/In concentration ratios and elemental Se in liquid phase of flux material in evacuated quartz ampoules. The surface morphology, phase structure, and composition of the powder crystals were analyzed by scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray analysis respectively. Bulk composition was analyzed polarographically. Photoluminescence spectra were measured at 9 K. It was found that the composition of MGP material (Cu/In concentration ratio) can be controlled by the concentration ratio of precursor Cu-In alloys. Single phase CuInSe2 growth is realisable between 0.7<Cu/In<1 at the growth temperature of 1000 K. Photoluminescence spectra of near-stoichiometric materials had one dominant peak at 0.93 eV, which is typical to In-rich CuInSe2. Samples with high In content exhibited two broad bands with peak positions at 0.86 and 0.93 eV.
Rapid Thermal Annealing on Cu(In,Ga)Se2 Films and Solar Cells
Authors: Wang Xuege , Li Sheng. S. , Craciun V. , Yoon S. , Howard J. M. , Easwaran S. , Manasreh O. , Crisalle O. D. , Anderson T. J. 
Published: November 2011

AbstractRapid thermal annealing (RTA), with fast ramp up and down rates, was performed on several Cu(In,Ga)Se2 (CIGS) films and solar cells under various peak annealing temperatures and holding times. The XRD, SEM, Hall- effect, photo J-V, and quantum efficiency (Q-E) measurements were made on CIGS films and cells before and after RTA treatments to study the effects of RTA on the CIGS film properties and cell performance. The results show that RTA treatments under optimal annealing condition can provide significant improvements in the electrical properties (resistivity, carrier concentration, and mobility) of CIGS films and cell performance while preserving the film composition and microstructure morphology.
Large Area Cu(In,Ga)Se2 Films and Devices on Flexible Substrates Made by Sputtering
Authors: Hollars Dennis R. , Dorn Randy , Paulson P. D. , Titus Jochen , Miasolé Robert Zubeck 
Published: November 2011

AbstractA reactive sputtering process was developed for the production of Cu(In,Ga)Se2 films on a moving stainless steel substrate, in simulation of the operation of a roll coater. Cu, In and Ga fluxes were provided through magnetron sputtering and were reacted in a flux of Se on the heated substrate. CdS films were deposited either by chemical bath deposition (CBD) or by sputtering. Devices of the type steel/Cr/Mo/CIGS/CdS/ZnO/Ag were completed by sputtering ZnO layers and by screen printing grid lines. We made devices with efficiency values above 9%. A uniformity study was performed on a CIGS film and on small area devices made from it. The target length was 12”. Targets of this size are expected to produce a uniformly thick deposit over a range of 6-8”. The film thickness was 2.54 μm over a range of 6” with a standard deviation ó of 0.04 μm. The film composition was uniform over a range of 16”. The values of Cu/III and Ga/III were 0.84 and 0.31, with ó values of 0.02 and 0.01, respectively. The efficiency of allsputtered devices was uniform over a range of 12”, well beyond the 6” wide range of constant CIGS film thickness. Their efficiency was 6.6% on average with ó=0.6%.
Transparent ZnTe:Cu contacts for bifacial characterization of CdTe solar cells
Authors: Desai Darshini , Hegedus Steven , McCandless Brian , Ryan Daniel 
Published: November 2011

AbstractCu-doped ZnTe films grown by galvanic deposition were developed to provide transparent ohmic contacts to CdTe solar cells. Control of the Cu doping with triethanolamine was critical to limit the free Cu in order to achieve high transparency (>60% in the visible) and to minimize shunting. Devices with ZnTe:Cu contacts had comparable performance to devices with Cu/Au or Cu/graphite contacts, achieving Voc of 0.79 V and fill factor (FF) of 68% for standard front illumination. Bifacial spectral response (SR) measurements, through front and back contacts, were analyzed and yielded a diffusion length (L) of 0.8 μm and depletion width (W) of 2.5 μm. Backwall SR measurements made through the transparent ZnTe contact are much more sensitive to L and W than are measurements for standard front illumination. ZnTe:Cu is a promising material for bifacial characterization as well as tandem cell interconnects and more stable Cu-doped contacts.
Characterization of the Electronic Properties of Wide Bandgap CuIn(SeS)2 Alloys
Authors: Halverson Adam F. , Erslev Peter T. , Lee JinWoo , David Cohen J. , Shafarman William N. 
Published: November 2011

AbstractThe electronic properties of sulfur containing CIS chalcopyrite alloys have been characterized using junction capacitance methods. Two devices were examined; one containing CuIn(S,Se)2 alloy with a 1:2 S:Se ratio and a bandgap near 1.15eV, and the other an endpoint CuInS2 alloy with a bandgap slightly above 1.5eV. Drive-level capacitance profiling measurements indicated hole carrier densities of less than 1 x 1015 cm-3 and 1.5 x 1016 cm-3, respectively. Transient photocapacitance (TPC) sub-bandgap spectroscopic measurements revealed sharp bandtails plus a broad defect band within the bandgap of each alloy. The TPC spectra for the CuInS2 sample revealed a couple of unusual features, including a bandtail signal that reversed sign below 250K. This indicated poorer hole collection than electron collection in the low temperature regime. Comparing these results to TPC spectra obtained previously for Cu(InGa)Se2 alloys indicate some similarities but also some striking differences.
Band gap fluctuations in Cu(In,Ga)Se2 thin films
Authors: Mattheis Julian , Schlenker Thomas , Bogicevic Martin , Rau Uwe , Werner Jürgen H. 
Published: November 2011

AbstractA simple statistical model describes measured absorption and photoluminescence data of Cu(In1-x, Gax)Se2 thin films. The broadening of the transition peak in the absorption spectra stems from band gap fluctuations. The extent of the spatial inhomogeneities as expressed in the standard deviation Eg μ reaches a maximum of Eg μ = 90 meV for films with equal amounts of indium and gallium, indicating alloy disorder as one possible source of the band gap fluctuations. The fluctuations observed lead to a decrease δVOC of the maximum possible open-circuit voltage VOC of almost 150 mV. However, the experimentally measured, low VOC of solar cells with high gallium content cannot be explained by band gap fluctuations alone. Consequently, our analysis suggests that the dominant recombination process in Cu(In1-x, Gax)Se2 thin film solar cells with high gallium content is not governed by the band gap energy, but is more likely due to deep levels within the forbidden gap.
Band structure investigation of chalcopyrite CuInSe2(001) by angle-resolved photoelectron spectroscopy
Authors: Hunger Ralf , Pettenkofer Christian 
Published: November 2011

AbstractClean and ordered chalcopyrite CuInSe2 surfaces are a precondition for the study of the electronic structure by angle-resolved photoelectron spectroscopy. The preparation of welldefined CuInSe2(001) surfaces by the combination of molecular beam epitaxy and a selenium capping and decapping process is described. The surface structure of CuInSe2 epilayers with different bulk composition is compared and analysed by low-energy electron diffraction.Employing near-stoichiometric surfaces, the valence electronic structure of CuInSe2 was investigated by angle-resolved photoelectron spectroscopy at the synchrotron source BESSY 2. This is the first study of the valence band structure of a copper chalcopyrite semiconductor material by photoelectron spectroscopy. The valence band dispersion along τT, i.e. the [001] direction, was investigated by a variation of the excitation energy from 10 to 35 eV under normal emission, and the band dispersion along τT, i.e. the [110] direction, was analysed by angular scans with hv = 13 eV.The valence bands derived from antibonding and bonding Se4p-Cu3d hybrid orbitals, nonbonding Cu3d states and In-Se hybrid states are clearly indentified. The strongest dispersion is found for the topmost valence band with a bandwidth of ∼0.7 eV from τ to T. From τ to N, the observed dispersion was 0.5 eV. The experimental valence bands are discussed in relation to calculated band structures in the literature.
Photovoltaic Effect in the Anisotype GaSe-InSe Heterojunctions Under Pressure
Authors: Drapak S.I. , Vorobets M.O. , Kovalyuk Z.D. 
Published: November 2011

AbstractThe influence of mechanical pressure along the direction across the interface of n-InSe-p-GaSe heterojunctions on saturation photo-e.m.f. and short-circuit current is investigated. It is shown that at the InSe/GaSe optical contacts subjected to a pressure P = 35-40 kPa an increase of the open-circuit voltage nearly twice and short-circuit current more than by a factor of five in comparison to the initial samples takes place. It makes possible to predict a possibility of considerable increasing photoconversion efficiency of such structures.
The Optical Properties of the Interface Layer in CdS-CdTe Heterojunctions
Authors: Vatavu Sergiu A. 
Published: November 2011

AbstractThe photosensitivity and electro-reflection spectra of CdS/CdTe heterojunctions annealed up to one hour in presence of CdC12 have been studied. The lifetime of charge carriers, generated in the interface layer, has been determined.The SnO2/CdS/CdTe/Ni thin films solar cells, deposited by close-spaced sublimation (CSS) technique are photosensitive in the 1.5-2.4 eV spectral region. The spectral distribution of photocurrent is not essentially modified by the increase of the annealing time. A slight decrease of the photocurrent in the 1.5-1.7 eV energy range is observed and the photocurrent slightly increases in the 1.7-2.4 eV region. The recombination of the nonequilibrium charge carriers in the interface layer takes place via recombination levels having a lifetime value, which decreases from 46 μs down to 30 μs along with photon energy increase from 1.55 eV to 2.4 eV respectively (T=293K). The correlation between the light penetration depth in component layers, estimated from the absorption spectral distribution and the photon energies was established.
Complex defect behavior in Cu(In,Ga)Se2 solar cells with different gallium content
Authors: Mertens Verena , Parisi Jürgen , Kniese Robert , Köntges Marc , Reineke-Koch Rolf 
Published: November 2011

AbstractWe report on capacitance spectroscopy measurements on Cu(In,Ga)Se2 based solar cells where the gallium content was varied systematically. In all samples we found, depending on the measurement conditions, a minority carrier and/or a majority carrier signal. The minority trap can be attributed to the prominent donor-like state N1 or â already discussed in literature. However, the origin of the majority trap remains unclear.
TEM Studies of High-Efficiency CdTe Solar Cells on Commercial SnO2/Soda-Lime Glass
Authors: Yan Yanfa , Wu X. , Zhou J. , Al-Jassim M.M. 
Published: November 2011

AbstractThe microstructure of high-efficiency CdTe solar cells on commercial SnO2/soda-lime glass was investigated by scanning transmission electron microscopy. The CdTe solar cells have a structure of soda-lime glass/SnO2/ZTO/CdS:O/CdTe. We found no interdiffusion between the SnO2 layer and ZTO layer. Weak diffusion of Zn from the ZTO layer into the CdS:O layer was observed; however, the diffusion was not uniform. Interdiffusion also occurred at the CdTe/CdS:O interface. In the back-side of the CdTe, a thin layer of Te was found, which formed during the nitric-phosphoric etching. In addition, a very thin layer of CdHgTe was observed at the CdTe/Te interface.
p-ZnTe for Back Contacts to CdTe Thin Film Solar Cells
Authors: Späth Bettina , Fritsche Jochen , Klein Andreas , Jaegermann Wolfram 
Published: November 2011

AbstractCdTe thin film solar cells still suffer from problems related to back contacts which provide stable ohmic contacts without electrical losses. In previous studies metal/CdTe contacts have shown significant limitations. A promising option for the realization of ohmic back contacts is the use of a highly p-doped ZnTe interlayer on top of the CdTe absorber, in particular since metal/ZnTe contacts have shown very good electrical properties. In this work we studied the electronic und chemical properties of nitrogen doped p-ZnTe films. p-ZnTe:N films were prepared by using reactive RF magnetron sputtering with N2/Ar gas mixtures or by thermal evaporation with an additional nitrogen plasma source. Samples and their contacts have been prepared in DAISY-SOL (DArmstadt Integrated SYstem for SOLar energy research) which combines a full vacuum production with an in-situ photoelectron spectroscopy (XPS/UPS) analysis. The results of XPS/UPS investigations and electrical measurements will be discussed in comparison to previous results on metal/CdTe contacts. As ZnTe forms an interlayer in the CdTe thin film solar cell, the ZnTe/CdTe interface properties must be also taken into consideration. Our experiments have shown in agreement to previous studies that the valence band offset is nearly ideal for hole transport across the interface. Also electrical measurements have been carried out to investigate the metal/ZnTe/CdTe layer sequences in their contact properties.
A Calibrated Multiclass Extension of AdaBoost
Authors: Rubin Daniel B. 
Published: November 2011

AdaBoost is a popular and successful data mining technique for binary classification. However, there is no universally agreed upon extension of the method for problems with more than two classes. Most multiclass generalizations simply reduce the problem to a series of binary classification problems. The statistical interpretation of AdaBoost is that it operates through loss-based estimation: by using an exponential loss function as a surrogate for misclassification loss, it sequentially minimizes empirical risk through fitting a base classifier to iteratively reweighted training data. While there are several extensions using loss-based estimation with multiclass base classifiers, these use multiclass versions of the exponential loss that are not classification calibrated: unless restrictions are placed on conditional class probabilities, it becomes possible to have optimal surrogate risk but poor misclassification risk. In this work, we introduce a new AdaBoost extension called AdaBoost.SL that does not reduce the problem into binary subproblems and that uses a classification-calibrated multiclass exponential loss function. Numerical experiments show the algorithm performs well on benchmark datasets.
The Use of the Lapidus Procedure for Recurrent Hallux Valgus
Authors: Ellington J. Kent , Myerson Mark S. , Coetzee J. Chris , Stone Rebecca M. 
Published: November 2011

Background: The objective of this study was to evaluate the Lapidus procedure or it's modifications for treatment of recurrent hallux valgus (HV). Our hypothesis was that the Lapidus procedure would achieve good correction of recurrent HV and patients would be satisfied. Materials and Methods: A retrospective review of 32 feet (30 patients) treated with the Lapidus procedure for recurrent HV with at least 1-year followup was performed. Evaluation included radiographs, examination, and chart review. Outcomes were assessed with a pain visual analog scale (VAS), American Orthopaedic Foot and Ankle Society (AOFAS) hallux score, SF-12, Revised Foot Function Index (RFFI), and a survey. Twenty-three of 30 patients (25 feet) met the criteria for inclusion in the study and were available for followup evaluation. The average followup was 31.6 months. Results: Arthrodesis was present in 24 out of 25 feet (96%). The time from initial HV correction to revision surgery was 91 months. The initial surgery performed was a distal osteotomy (15), proximal osteotomy (five), exostectomy (two), diaphyseal osteotomy (two), and proximal/distal osteotomy (one). Preoperative evaluation revealed 96% of patients had clinical hypermobility of the first TMT joint and 52% had radiographic findings of instability. The average postoperative AOFAS hallux score was 82.8, SF-12 score was 94.5, and RFFI was 101. The average preoperative hallux valgus angle (HVA), intermetatarsal angle (IMA), and distal metatarsal articular angle (DMAA) were 36.2, 13.6,18.6 degrees, respectively, which corrected to an average of 15.2, 7.5, 11.7 degrees postoperatively (p < 0.001). The average shortening of the first ray was 2.9 mm. Average pain VAS was 2.4. Eighty-seven percent reported good to excellent results. Using a multivariable linear regression analysis, postoperative HVA along with change in length of the first ray were significant predictors of quality of life based on SF-12 ( p < 0.05). Conclusion: The Lapidus procedure corrected recurrent HV with a low nonunion rate and excellent radiographic correction and patients were satisfied with their outcome. Level of Evidence: IV, Retrospective Case Series
Outcomes following Pantalar Arthrodesis in Rheumatoid Arthritis
Authors: McKinley John C. , Shortt Nicholas , Arthur Calum , Gunner Charlotte , MacDonald Deborah , Breusch Steffen J. 
Published: November 2011

Background: We report a consecutive series of pantalar arthrodeses in patients with rheumatoid arthritis, using a single laterally based incision and autologous bone graft. Materials and Methods: All operations were performed by a single surgeon and were assessed preoperatively and at 6 and 12 months postoperatively. The levels of patient satisfaction, functional improvement, and pain scores of the foot following surgery were recorded along with radiological parameters. Seventeen patients (two male and 15 female) underwent 18 hindfoot surgeries and were assessed preoperatively using the SF-12 General Health survey questionnaire, Manchester-Oxford Foot Survey, and pain scores. Results: We found a significant improvement in pain levels and SF-12 scores. In addition, the patients reported a high level of satisfaction with the outcome of surgery and improvement in function. Conclusion: The results show that pantalar arthrodesis is a very effective operative treatment for severe ankle and concomitant hindfoot disease. The treatment period is prolonged and patients should be counseled appropriately. Level of Evidence: IV, Retrospective Case Series
The Slot Graft Technique for Foot and Ankle Arthrodesis in a High-Risk Patient Group
Authors: Klein Sandra E. , Putnam Ryan M. , McCormick Jeremy J. , Johnson Jeffrey E. 
Published: November 2011

Background: High rates of arthrodesis nonunion have been described in the ankle, hindfoot and midfoot in patients with significant risk factors. The purpose of this study was to evaluate fusion rates, risk of reoperation, postoperative pain scores and patient satisfaction for a slot graft inlay arthrodesis technique used in a high-risk group of foot and ankle patients. Materials and Methods: We retrospectively reviewed all ankle, hindfoot and midfoot arthrodeses by two foot and ankle surgeons in our institution between January 2000 and January 2009. Seventeen arthrodesis procedures in 16 patients using the slot graft technique were identified. Patient charts were reviewed for medical history, risk factors, previous surgery and postoperative complications. Time to union was evaluated on radiographs. Patients provided final followup by phone with an assessment of pain, overall satisfaction and use of orthotic or assistive devices. Results: Union occurred in 13 arthrodesis procedures (77%) with an average time to union of 5 months. Postoperative infection occurred in one patient. Additional surgery was performed in nine patients. At final followup patients reported low pain scores (3 of 10) and high satisfaction (8 of 10). Fourteen of 15 patients contacted indicated that they would choose to undergo the procedure again. Conclusion: The slot graft arthrodesis technique provided satisfactory results in this small group of patients with a low complication rate. Patient satisfaction rates were high with low pain scores at an average of 62 months postoperatively. Level of Evidence: IV, Retrospective Case Series