Thin-Film Cadmium Sulfide/Cadmium Telluride Alloys

Jensen, D. G.; McCandless, Brian E.; Birkmire, R.W.

doi:10.1557/proc-426-325

Cited by 37 publications

(24 citation statements)

References 9 publications

(8 reference statements)

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“…• For all annealing temperatures studied here, the maximum S concentration is observed to be around 5% which is quite close to the S solubility limit at 415 0 C of 5.8% reported in [16]. (2) The presence of distinct CdTe and CdTe 1-x S x phases within the film after 410 0 C anneal is quite interesting.…”

Section: X-ray Diffractionsupporting

confidence: 84%

Polycrystalline Thin-Film Cadmium Telluride Solar Cells Fabricated by Electrodeposition; Final Technical Report, 20 March 1995-15 June 1998

Trefny¹,

Mao²,

Kaydanov³

et al. 1999

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EXECUTIVE SUMMARY ObjectivesOne of the objectives of this project is to develop improved processes for the fabrication of high-efficiency CdTe/CdS polycrystalline thin film solar cells. The technique we use for the formation of CdTe, electrodeposition, is a non-vacuum, low-cost technique that is attractive for economic, large-scale production. The other objective was to study cell degradation, using stability tests under stress conditions and analysis of possible degradation mechanisms. Technical ApproachOur research and development efforts have focused on several steps that are most critical to the fabrication of high-efficiency CdTe solar cells. These include the optimization of the CdTe electrodeposition process, the effect of pre-treatment of CdS substrates, the post-deposition annealing of CdTe, and back contact formation using Cudoped ZnTe. Systematic investigations of these processing steps have led to better understanding and improved device performances of the CdTe-based solar cells.Stability tests under enhanced temperature showed that cell efficiency degradation is due mainly to an increase in "series resistance". Therefore the degradation processes studies were focused mostly on revealing and explaining the changes that occur in the back-contact region and in the bulk CdTe due to the ZnTe:Cu back contact presence. These changes were studied by means of detailed analyses of the cell I-V characteristics, the C-V profile in the CdTe, and compositional changes in the back-contact region. When discussing possible mechanisms of degradation, the compensation phenomena and charged impurities electromigration were taken into account. Major Results and ConclusionsCdS thin films prepared by chemical bath deposition. Film growth and structure.The structural properties of the films and the growth mechanisms were studied by investigating CdS samples prepared at different deposition times. A duplex structure with an inner compact layer and an outer porous layer and three growth stages can explain our data. The measurement of refractive index as a function of deposition time provides a simple way to determine the transition point from compact layer growth to porous layer growth, which is important for the optimization of CdS growth conditions in photovoltaic applications. Careful XRD analyses allowed unambiguous determination of crystal properties.Electrodeposited CdS Thin Films and their application.Electrodeposition is a non-vacuum technique and is compatible with our CdTe deposition process. It offers excellent control over the properties of the thin films through the influence of deposition potential, bath temperature, pH, and composition of reactants. In 2 this project preliminary studies were performed on the electrodeposition of CdS and its application in fabricating CdTe/CdS solar cells. The influence of deposition conditions on the film deposition rate, composition and morphology was studied. CdTe/CdS cells using electrodeposited and physical vapor deposited CdTe on electrodeposited CdS were prepared and ch...

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Section: X-ray Diffractionsupporting

confidence: 84%

Polycrystalline Thin-Film Cadmium Telluride Solar Cells Fabricated by Electrodeposition; Final Technical Report, 20 March 1995-15 June 1998

Trefny¹,

Mao²,

Kaydanov³

et al. 1999

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“…For mixed crystal films formed at lower temperatures, from 120°C to 200°C, a continuous range of alloys can be obtained [31,33,35,36,37]. For the mixed films, heating above ~300°C induces phase segregation in accordance with the existence of the equilibrium miscibility gap found in mixed CdTe-CdS crystals at higher temperature, indicating that single phase films with composition lying within the miscibility gap are deposited in a metastable state.…”

Section: Solubility Limit Determinationmentioning

confidence: 84%

“…The mixed films were evaporated from CdS and CdTe powders, forming meta-stable alloys with mid-range composition ~CdTe 0.5 S 0.5 . Heat treatment of these films in CdCl 2 :O 2 :Ar vapor resulted in phase segregation into two alloy components at each side of the CdTe-CdS equilibrium miscibility gap [31]. To ensure that end-point compositions were reached at each temperature, the treatment time was extended until the measured change in alloy compositions were less than the detection limit, which, for x and y, is ~0.0001.…”

Section: Solubility Limit Determinationmentioning

confidence: 99%

“…Formation of the CdS 1-y Te y alloy on the S-rich side of the junction reduces the bandgap and increases absorption, reducing photocurrent in the 500 to 600 nm range [45]. Formation of the CdTe 1-x S x alloy on the Te-rich side of the junction reduces the absorber layer bandgap, due to the optical bowing parameter of the CdTe-CdS alloy system [31]. The increase in long wavelength spectral response increases photocurrent by ~ 0.5 mA/cm 2 , which is nearly offset by small reduction in V oc ~ 25 mV.…”

Section: Processing Sequences To Control Cds Consumptionmentioning

confidence: 99%

“…In this case, CdS consumption can be limited by reducing grain boundary diffusion, CdCl 2 and O 2 vapor concentrations and treatment temperature. A viable processing route already established for minimizing CdS consumption is utilizing uniform CdTe 1-x S x alloy absorber layers in place of pure CdTe [47].…”

Section: Controlling Cds Diffusionmentioning

confidence: 99%

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Optimization of Processing and Modeling Issues for Thin Film Solar Cell Devices Including Concepts for the Development of Polycrystalline Multijunctions Annual Subcontract Report, 24 August 1999 - 23 August 2000

Birkmire¹,

Phillips²,

Shafarman³

et al. 2001

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SUMMARYThe overall mission of the Institute of Energy Conversion (IEC) is the development of thin film photovoltaic cells, modules, and related manufacturing technology and the education of students and professionals in photovoltaic technology. The objectives of this 12 month NREL subcontract are to advance the state of the art and the acceptance of thin film PV solar cells in the areas of improved technology for thin film depositions, device fabrication, and material and device characterization and modeling, relating to solar cells based on CuInSe2 and its alloys, on doped and intrinsic microcrystalline Si films, and on CdTe. CuInSe 2 -BASED SOLAR CELLS In-line Evaporation of Cu(InGa)Se 2In-line evaporation is a potentially effective means to achieve the high rate uniform deposition necessary for commercial-scale manufacture of Cu(InGa)Se 2 modules. In this process, the substrate is linearly translated over thermal sources from which the elemental materials are evaporated.An in-line evaporation system for the deposition of Cu(InGa)Se 2 films has been put into operation at IEC. The system's performance in terms of uniform deposition over large areas at relatively high rates and in terms of device performance and reproducibility has been successfully demonstrated. The compositional uniformity across the 6-inch wide deposition zone is within the uncertainty limits of EDS measurements. A set of depositions with translation speeds ranging from 1 to 2.5 inches/min produced films with thicknesses from 2.1 to 0.9 µm. Devices from these runs had efficiencies from 13.2-14.5 %, for thickness > 1 µm, demonstrating the run-to-run reproducibility of the system. The best cell produced with Cu(InGa)Se 2 from this in-line system had 14.9% efficiency. Effect of Deposition Temperature on Cu(InGa)Se 2 Films and DevicesOne means to reduce manufacturing costs for thin film Cu(InGa)Se 2 is by reducing the substrate temperature at which the Cu(InGa)Se 2 layer is deposited. The effect of substrate temperature on the film grain size, morphology, and compositional uniformity and device performance of Cu(InGa)Se 2 deposited at 480°C was characterized and compared to previous results at 400°C and 550°C. At 480°C, the soda lime glass substrate is below the strain point of the glass, reducing handling problems.Cu(InGa)Se 2 films were deposited by multisource elemental evaporation with different deposition sequences to determine the effect of a Cu-rich growth step, i.e., deposition with the Cu molar flux greater than the sum of the In and Ga fluxes. The grain size was determined from atomic force microscopy images. The films deposited at 480°C have comparable grain size and morphology to those deposited at 550°C. However, V oc , FF, and efficiency of devices with films deposited at 550°C were greater. A Cu-rich growth step during the deposition does not affect the measured grain size or device performance at these temperatures. The films deposited at 400°Ciii have smaller grains and poorer device performance. At this lower temperature the Cu-...

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Cadmium Telluride Solar Cells

McCandless

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Handbook of Photovoltaic Science and Engineering

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Thin-Film Cadmium Sulfide/Cadmium Telluride Alloys

Cited by 37 publications

References 9 publications

Polycrystalline Thin-Film Cadmium Telluride Solar Cells Fabricated by Electrodeposition; Final Technical Report, 20 March 1995-15 June 1998

Polycrystalline Thin-Film Cadmium Telluride Solar Cells Fabricated by Electrodeposition; Final Technical Report, 20 March 1995-15 June 1998

Optimization of Processing and Modeling Issues for Thin Film Solar Cell Devices Including Concepts for the Development of Polycrystalline Multijunctions Annual Subcontract Report, 24 August 1999 - 23 August 2000

Cadmium Telluride Solar Cells

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