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Photovoltaic Specialists Conference (PVSC), 2013 IEEE 39th

Date 16-21 June 2013

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Displaying Results 1 - 25 of 791
  • Cover page

    Page(s): 1
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  • Program at-a-glance

    Page(s): 1
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  • Table of contents

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  • Chairman's message

    Page(s): 1 - 78
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  • Author/Presenter index

    Page(s): 246 - 272
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  • Technical program

    Page(s): 75 - 240
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  • Copyright page

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  • Rating photovoltaics

    Page(s): 0001 - 0006
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (205 KB) |  | HTML iconHTML  

    The rating of photovoltaic (PV) cells and modules is critical in comparing the performance of the plethora of competing PV technologies. The rating should be easy to reproduce, give a unique value in the absence of measurement error, and, most importantly, be directly related to the expected system performance. PV rating methods have evolved since the first measurement workshop in 1975. Consensus standards exist and the PV community is in agreement on how to rate most PV technologies for terrestrial and space applications. There is still disagreement on the proper probing for Si wafers and how to test low-concentration, bifacial cells. Because of the low demand, there has been little effort to standardize rating PV for indoor or other applications that do not involve bulk power generation as their primary activity. View full abstract»

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  • Validation of the PVLife model using 3 million module-years of live site data

    Page(s): 0007 - 0012
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (751 KB) |  | HTML iconHTML  

    Establishing a strong basis for confidence in a solar technology requires being able to prove a low-degradation track record in the real world, and rationalize it with strong physical understanding and investigation. This paper briefly reviews our previously-published physical model for calculating degradation and reliability, PVLife, which computes hour-by-hour degradation of PV modules using weather files and degradation sub-models developed from accelerated test data. We then demonstrate a validation of this model against a large statistical data set obtained from 266 systems powered by SunPower modules (data from over 179 systems installed by Powerlight, using non-SunPower modules are also shown). In total these data represent over 800,000 modules and a total of 3.2 million module-years of experience. The data analysis technique requires little manual data processing and can be derived from live sites without special experimental treatment. We also discuss returnrate data on modules incorporating SunPower's back-contact cell, as well as front contact modules in SunPower's fleet. Implications for failure prediction are discussed. View full abstract»

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  • Routes to high efficiency photovoltaic power conversion

    Page(s): 0013 - 0016
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (441 KB) |  | HTML iconHTML  

    The thermodynamic efficiency limit for solar power conversion sits at 87% yet the majority of photovoltaic devices operate at efficiencies of 20% or less. Multi-junction solar cells presently represent the most accessible technological route to high efficiency and are now operating close to the radiative limit, where optical coupling between sub-cells becomes significant. Alternatively, sequential absorption of photons within a single material can be used to achieve efficiencies comparable to a triple junction solar cell, however the relatively low flux of solar photons places constraints around the acceptable lifetime and mobility of excited carriers. Finally thermal gradients in solar cells have been shown to yield small efficiency enhancements. The only means to achieve high efficiency using thermal gradients is by isolating the carrier population from the lattice as proposed in the hot carrier solar cell. View full abstract»

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  • Towards high-efficiency ultra-thin solar cells with nanopatterned metallic front contact

    Page(s): 0017 - 0021
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1213 KB) |  | HTML iconHTML  

    We propose a novel design using multi-resonant absorption to achieve efficient light-trapping in ultra-thin (<; 100 nm) solar cells. It is based on a patterned metallic layer which i) strongly confines light in an ultra-thin and flat absorber layer and ii) plays the role of a front contact combining high optical transparency and good electrical conductivity. This versatile approach is applied to different solar cells materials (a-Si:H, GaAs) and geometries of the patterned film (1D or 2D). We demonstrate a theoretical conversion efficiency over 20 % using a 2D silver nanogrid to enhance absorption in a 25 nm-thick GaAs absorber layer. First demonstrators were fabricated and optically characterized. This work should pave the way towards high-efficiency ultra-thin solar cells. View full abstract»

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  • Al nanoparticle arrays for broadband absorption enhancements in GaAs devices

    Page(s): 0022 - 0024
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (636 KB) |  | HTML iconHTML  

    We present the results of a series of comprehensive simulations comparing the performance of GaAs solar cells with periodic arrays of Au, Ag and Al nanoparticles on the front surface. Using optical and electronic calculations we show that the choice of scattering material is crucial to minimize parasitic losses and achieve broadband absorption enhancements. In particular, we demonstrate that by using Al nanoparticle arrays the optical absorption can be enhanced across a spectral range from 350-900 nm leading to an increase in power conversion efficiency of more than 45 % compared to a flat cell. View full abstract»

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  • Photoluminescence enhancement towards high efficiency plasmonic solar cells

    Page(s): 0025 - 0028
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1011 KB) |  | HTML iconHTML  

    We demonstrate enhanced absorption in silicon wafers when plasmonic nanoparticles are added to a conventional rear contact structure. A rear side light trapping with plasmonic nanoparticles and various thicknesses of Si3N4 layer is studied and compared to a structure with combined plasmonics and diffused paint. Photoluminescence is applied to extract the absorptivity in order to exclude free carrier and parasitic absorption. Modeling shows that the absorption within a cell structure with plasmonic nanoparticles and optimum capping layer is expected to be enhanced by 53% of value for an ideal Lambertian reflector. View full abstract»

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  • Towards Lambertian internal light scattering in solar cells using coupled plasmonic and dielectric nanoparticles as back reflector

    Page(s): 0029 - 0033
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB) |  | HTML iconHTML  

    We present a novel approach that opens the route to exceeding the 4n2 light trapping limit. White paint, usually based on titanium dioxide (TiO2) nanoparticles, is well known for its high reflectance and excellent light scattering properties. The angular intensity distribution (AID) is close to the ideal Lambertian cos(φ) distribution when light is scattered into air. White paint therefore seems to be the ideal back reflector for solar cell applications. However, when white paint scatters light into c-Si, the AID is refracted into a narrower cone, leading to a large deviation from the Lambertian scattering. Here we present an effective approach to avoid this refraction effect and significantly improve light trapping. Our approach is based on combining dielectric TiO2 nanoparticles with plasmonic silver nanoparticles. The dielectric particles efficiently couple the incident light to the plasmonic particles which in turn couple the light into the absorber layer. Because plasmonic nanoparticles can couple the light beyond the critical angle, the resulting AID inside the absorber is much broader than without the plasmonic particles. We show that this leads to improved light trapping and solar cell performance. View full abstract»

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  • High efficiency Cu2ZnSnS4 nanocrystal ink solar cells through improved nanoparticle synthesis and selenization

    Page(s): 0034 - 0037
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1171 KB) |  | HTML iconHTML  

    In this work we present the improved efficiency of nanocrystal ink based Cu2ZnSn(S, Se)4 (CZTSSe) solar cells to 9.15%. CZTSSe devices prepared from nanocrystal inks are known for the presence of an unintended amorphous/fine-grained layer (unsintered layer) near the back contact. We demonstrate the ability to reduce the proportion of the unsintered layer in the final film through improved nanocrystal synthesis techniques and tailored thermal annealing in selenium atmosphere (selenization). Interestingly, our selenization process has not led to similar device performance in films prepared from particles using other recipes from the literature. View full abstract»

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  • Solution-processed Cu2ZnSn(S, Se)4 solar cells — Various impacts on morphology and performance

    Page(s): 0038 - 0042
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1449 KB) |  | HTML iconHTML  

    In this work the morphology and performance of thin-film solar cells with a kesterite-type Cu2ZnSn(S, Se)4 absorber are investigated. The preparation is based on a metal salt solution with dimethyl sulfoxide as solvent, which is deposited on a molybdenum coated substrate via doctor-blade coating and subsequently annealed in selenium-containing nitrogen-atmosphere. To learn more about the originating trilayer structure of the absorber, precursor layers of different thickness were prepared and temperature and duration of the annealing process were varied. View full abstract»

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  • Effect of the selenization process on structural and device properties of nanoparticle-derived CZTSSe thin films

    Page(s): 0043 - 0046
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (847 KB) |  | HTML iconHTML  

    Cu2ZnSn(S,Se)4 thin films and solar cells were fabricated using binary and ternary nanoparticle precursor films selenized using three different processes. Cross-sectional SEM images of the resulting CZTSSe solar cells do not show significant difference in microstructure. Detail analyses of the CZTSSe solar cells using current-voltage (J-V), external quantum efficiency (EQE), temperature-dependent J-V, and admittance spectroscopy (AS) were conducted to investigate the effect of the selenization process on the optical and electrical properties of the absorber. View full abstract»

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  • Influence of carrier density spatial heterogeneities on the electrical breakdown of crystalline silicon solar cells: Experiment and simulation

    Page(s): 0047 - 0050
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2209 KB) |  | HTML iconHTML  

    In this work we investigate how spatial heterogeneities of the substrate hole density influence the reverse characteristics of UMG solar cells. Electroluminescence and current-voltage data on highly heterogeneous cells are compared with the predictions of TCAD simulations. Reverse-bias electroluminescence images reveal that the distribution of breakdown sites follows the general pattern of the carrier density distribution, but are highly localized at some specific defects. Measurements show that the overall breakdown voltage is governed by the highest carrier density across the wafer, suggesting that this maximum density should be controlled with care. These results are in good agreement with simulation showing that TCAD tools can successfully include the effect of spatial heterogeneities. View full abstract»

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  • Improved 750 °C epitaxial crystal silicon solar cells through impurity reduction

    Page(s): 0051 - 0053
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB) |  | HTML iconHTML  

    We characterize and improve epitaxial silicon films for solar cells grown by hot-wire chemical vapor deposition (HWCVD). The hot-wire filament temperature is found to affect the incorporation of impurities and the surface roughness of the films. Lowering the filament temperature leads to improved epitaxial films with lower impurities and smoother surfaces. Solar cells made with the improved material grown on low-cost silicon templates have open-circuit voltages (VOC) ~600 mV and efficiency exceeding 10%. View full abstract»

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  • 600 mV epitaxial crystal silicon solar cells grown on seeded glass

    Page(s): 0054 - 0057
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (297 KB) |  | HTML iconHTML  

    We report progress made at the National Renewable Energy Laboratory (NREL) on crystal silicon solar cells fabricated by epitaxially thickening thin silicon seed layers on glass using hot-wire chemical vapor deposition. Four micron thick devices grown on single-crystal silicon layer transfer seeds on glass achieved open circuit voltages (Voc) over 600 mV and efficiencies over 10%. Other devices were grown on laser crystallized mixed phase solidification (MPS) seeds on glass and e-beam crystallized (EBC) a-Si on SiC coated glass seeds. We discuss the material quality of the various devices on seeds and summarize the prospects for the seed and epitaxy PV approach. View full abstract»

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  • Enhancement of gettering in epitaxial thin-film silicon solar cells by tuning the properties of porous silicon

    Page(s): 0058 - 0062
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB) |  | HTML iconHTML  

    In epitaxial silicon solar cells grown on low-cost substrates, an embedded porous silicon layer is used to block metal diffusion from the substrate into the epitaxial active layer. The gettering efficiency of porous silicon can be enhanced by reducing the pore radius. In the size range (27.2 nm-39.8 nm) investigated, the additional curvature of the 27.2 nm void leads to >200 meV improvement in the binding energy for both copper and nickel, enhancing the gettering efficiency by >10 times. This is due to the existence of specific binding sites which allows greater dangling bond passivation in smaller voids. View full abstract»

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  • Epitaxial wafer equivalent solar cells with overgrown SiO2 layer and varying doping profile to reduce the influence of defects

    Page(s): 0063 - 0066
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (538 KB) |  | HTML iconHTML  

    Epitaxial wafer equivalent solar cells require a reflecting rear side to reach similar efficiencies as wafer based cells. This can be achieved by implementing a SiO2 layer using the epitaxial lateral overgrowth technique. In this work defect structure and density within the silicon layers are discussed. As defect densities rise towards the SiO2 layers, solar cells are fabricated with increasing sizes of moderately doped back surface fields to reduce their influence. Thereby, a benefit of 3 % absolute in efficiency is obtained. However, the best cell with an efficiency of 14.1 % is still limited by the reduced crystal quality. View full abstract»

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  • Device-dependent light-level correction errors in photovoltaic I-V performance measurements

    Page(s): 0067 - 0072
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (458 KB) |  | HTML iconHTML  

    Spectral corrections enable investigators to report key performance indicators (KPIs) for photovoltaic (PV) devices at standard reporting conditions (SRC). Important KPIs include short circuit current, open circuit voltage, maximum power, current at maximum power, voltage at maximum power, and fill factor. Spectral correction procedures typically include compensation for light-level variation monitored during a current-voltage (I-V) performance measurement of a PV device. ASTM measurement standards stipulate I-V curve corrections that include such compensation. For a PV device whose performance at 25°C is given by a common 5-parameter single-diode model, these corrections are shown not to be strictly valid. Considering systematic light-level offset and random light-level variation, we examine the potential magnitude of the I-V curve correction error and its effect on these KPIs. For specific PV device model parameters taken from the literature and assuming perfect measurements, the expected absolute relative error in the corrected maximum power is approximately 0.5% for a light level that is systematically below a 1-sun equivalent by 5% on average and varying at a 2% level. Such analyses can be used to quantify device-specific contributions to measurement uncertainty from light-level correction errors, and to limit such errors through measurement process control. Furthermore, these results suggest exploring an alternative approach to the light-level correction problem, in which I-V measurements would first be used to characterize the parameters of a suitable model of the PV device. This model would then be used to predict the device's I-V curve and KPIs at SRC. View full abstract»

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  • Fast and reliable spectral response measurements of PV cells using light emitting diodes

    Page(s): 0073 - 0075
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (454 KB) |  | HTML iconHTML  

    We present a measurement system for absolute differential spectral responsivity of solar cells based on high-powered LED arrays coupled to an optical light guide capable of large area illumination. Two different measurement techniques were developed and tested with the same measurement apparatus on a variety of solar cells. The first method is an individual LED lock-in technique that can be performed over a broad frequency range. The second method is based on synchronous multi-frequency optical excitation, called the Fourier transform (FT) technique, using the LEDs and detection with a spectrum analyzer. A scheme for providing light bias using the LEDs during either measurement scheme is discussed. View full abstract»

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  • Series resistance mapping of III-V multijunction solar cells based on luminescence imaging

    Page(s): 0076 - 0080
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (539 KB) |  | HTML iconHTML  

    A method for spatially resolved series resistance measurements of Ga0.5In0.5P/Ga(In)As/Ge triple-junction solar cells based on electro- and photoluminescence imaging is presented. The results gained from luminescence images of all three subcells clearly indicate the main contributions to the series resistance like interrupted gridfingers, the frontside metallization itself and the top cell emitter layer. Test cells with partially electron irradiated areas are used to demonstrate that the method is not sensitive to inhomogeneous dark I-V parameters. View full abstract»

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