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Photovoltaics, IEEE Journal of

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Early Access articles are new content made available in advance of the final electronic or print versions and result from IEEE's Preprint or Rapid Post processes. Preprint articles are peer-reviewed but not fully edited. Rapid Post articles are peer-reviewed and edited but not paginated. Both these types of Early Access articles are fully citable from the moment they appear in IEEE Xplore.

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Displaying Results 1 - 25 of 73
  • Spectrum Sensitivity, Energy Yield, and Revenue Prediction of PV Modules

    Page(s): 1 - 5
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    Predictive performance comparison has been made for four types of photovoltaics (PV) modules: cadmium telluride, multicrystalline silicon, copper indium gallium selenide, and monocrystalline silicon. Representative spectral response and nameplate specifications were used to determine the performance under operating conditions in Albuquerque, NM, USA. Hour-by-hour spectra were derived via archived meteorological data. Use of this modeled spectra enables sensitivity analysis of the energy yield and revenue potential of competing PV module types and determination of new target spectra for future design optimization. View full abstract»

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  • Efficiency Improvement in Nonprime Crystalline Silicon Solar Cells by Chemical Isolation of Shunts Under Front Metallization

    Page(s): 1 - 6
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    Yield loss due to the breakage and production of nonprime or off-spec cells in industrially produced crystalline silicon-based solar cells is around 1–2%. Nonprime cells identified based on their electrical properties are rejected after quality inspection. The cells that are rejected can be classified as nonprime for many reasons, such as poor edge isolation, presence of conductive paths through p-n junctions formed by print paste stains, paste-filled microcracks, inclusions, nonuniform emitter, and nonuniform antireflective coatings. Development of efficient and economically feasible repair methods for the repowering of nonprime cells will increase the overall yield of the solar cell industry and reduce costs. To isolate severe shunts under front metallization, we developed a two-step chemical etching process to remove front metallization and emitter. Removal of front metallization and emitter yielded the best isolation of shunts. Shunt isolation and efficiency gain achieved by the chemical etching process has been demonstrated on both mono- and multicrystalline silicon solar cells. View full abstract»

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  • Characterizations of Cu/Sn–Zn Solder/Ag Interfaces on Photovoltaic Ribbon for Silicon Solar Cells

    Page(s): 1 - 4
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    Sn-$bm x$Zn ($x = 9$, 25, and 50 wt%) alloy solders are applied in photovoltaic (PV) ribbon and connected with silicon solar cells. The interfacial microstructures, series resistance, and bonding strength of Sn-${bm x}$Zn PV modules are investigated. Cu${bf 5}$Zn${bf 8}$ and AgZn${bf 3}$ intermetallic compounds (IMCs) were found at the interfaces. The Zn content in the solder dominates the growth behavior of IMCs at the interface. The thickness of the Cu${bf 5}$Zn${bf 8}$ and AgZn${bf 3}$ IMC layer increased with increasing Zn content in the solder, and thus, the series resistance of the PV module also increased. The growth of IMCs can enhance the interfacial adhesion strength, but excess Zn overconsumes the Ag electrode, reducing the bond strength of the PV module. Applying low-Zn-content Sn-${bm x}$Zn solder to PV ribbon avoids overconsumption of the Ag layer and, thus, decreases the series resistance and internal stress. View full abstract»

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  • 3-D Simulation and Optimization of Organic Solar Cell With Periodic Back Contact Grating Electrode

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (491 KB)  

    In this paper, we report an investigation of the optical and electrical properties of an organic solar cell (OSC) with a back contact grating architecture through 3-D numerical simulations. By using finite-element methods for both optical and transport properties, we have modeled the behavior of OSC with a grating architecture and compared with a conventional planar structure. Based on these optoelectrical simulations, we optimized the back contact grating, obtaining an increment of up to 17.5% in power conversion efficiency with respect to a planar structured OSC. This enhancement is the result of an increase of both short-circuit current and fill factor. View full abstract»

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  • Performance Stabilization of CdTe PV Modules Using Bias and Light

    Page(s): 1 - 6
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    Reversible performance changes due to light exposure frustrate repeatable performance measurements on CdTe photovoltaic modules. It is common to use extended light exposure to ensure that measurements are representative of outdoor performance. We quantify the extent to which such a light-exposed state depends on module temperature and consider voltage bias in the dark to aid in stabilization. We evaluate the use of dark forward voltage bias to bring about a performance state equivalent to that obtained with light exposure, as well as to maintain a light-exposed state prior to standard test condition (STC) performance measurement. Our results indicate that the most promising method for measuring a light-exposed state is to use light exposure at controlled temperature followed by prompt STC measurement with a repeatable time interval between exposure and the STC measurement. View full abstract»

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  • High-Concentration Photovoltaics—Effect of Inhomogeneous Spectral Irradiation

    Page(s): 1 - 7
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    At high solar concentration, subtle optical and electrical effects in combination can have a substantial impact on photovoltaic power (PV) generation. We have identified such an effect through its clear signature: a “ripple” in the output current with respect to the pointing angle of the concentrated PV (CPV) system to sun direction. At small angular misalignment, this effect can lower cell current by as much as 15% at 1600x concentration in full sun. At medium concentration between 500 and 1000x, while not as clearly visible in single cells, the effect also reduces output by a smaller amount. The disappearance of the “ripple” signature at low concentrations below 300x indicates that the effect is not a linear effect, such as a light loss. We attribute the pronounced angular sensitivity of power output at high concentrations to a combination of inhomogeneous spectral irradiation incident on the multijunction solar cell and of the impact of the finite lateral resistance of the cell. View full abstract»

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  • Directional Heating and Cooling for Controlled Spalling

    Page(s): 1 - 7
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    The fabrication of thin solar cells by kerfless wafering techniques offers a high potential for the reduction of photovoltaic costs. We present an experimental setup for the exfoliation of thin crystalline silicon foils from a silicon substrate induced by the difference in thermal expansion coefficient of the silicon and an aluminum stressor layer at moderate temperatures. A moving temperature gradient across the substrate controls the crack propagation parallel to the silicon surface. We measure and simulate the spatial temperature distribution during thermal treatment and find that the direction of crack propagation is controlled by the temperature distribution. We detach foils with an area of 19.6 cm2 with thickness values ranging from 50 to 80 μm within one layer. The foils have a smooth surface with some irregularities near the edge. View full abstract»

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  • Electrical and Structural Analysis of Crystal Defects After High-Temperature Rapid Thermal Annealing of Highly Boron Ion-Implanted Emitters

    Page(s): 1 - 8
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (798 KB)  

    Ion implantation of boron is a promising technique for the preparation of p-type emitters in n-type cells. We use rapid thermal annealing with temperatures up to 1250 °C and annealing durations between 6 s and 20 min to anneal the implant-induced crystal defects. Experimental ${bm J}_{{bf 0}{bm e}}$ is compared with simulated and measured defect densities. Perfect dislocation loops are identified to be the dominating defect species after rapid thermal annealing (RTA) above 1000 °C. Even for emitters with ${bm J}_{{bf 0}{bm e}}$ values around 40 fA/cm2, defects are present within the valleys of the textured surfaces after annealing. On textured Al$_{bf 2}$O$_{bf 3}$-passivated boron emitters, we measure ${bm J}_{{bf 0}{bm e}}$ of 38 fA/cm2 for a sheet resistance around 80 Ω/□ after very short annealing processes (1 min at 1200 °C). View full abstract»

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  • Spectrally Resolved Interband and Intraband Transitions by Two-Step Photon Absorption in InGaAs/GaAs Quantum Dot Solar Cells

    Page(s): 1 - 5
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    Two-step photon absorption processes in a self-organized In$_{bf 0.4}$Ga$_{bf 0.6}$As/GaAs quantum dot solar cell have been investigated by means of infrared (IR) light-biased change in external quantum efficiency (ΔEQE) spectroscopy at 9 K. In this paper, not only interband transitions but intraband transitions were both spectrally resolved by utilizing wavelength tunable intense mid-IR pulsed laser as the IR bias light source. The obtained EQE enhancement was attributed from reexcitation of photocarriers captured by quantum dots. The bound-to-continuum intraband transition probability was estimated to be about 8% by irradiating 100-suns-equivalent IR bias light. View full abstract»

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  • Approaches for Developing a Regression Model for Sizing a Stand-Alone Photovoltaic System

    Page(s): 1 - 8
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3135 KB)  

    This paper proposes a methodology to develop a regression model for sizing a stand-alone photovoltaic (SAPV) system, thereby predicting the operational requirements of an SAPV system for a given location and the load conditions. The application of this methodology is demonstrated by developing a pair of regression models for a particular case of solar irradiation, load, and efficiency, which serve as main inputs to this model. The proposed model is based on the simulated long-term performance of an SAPV system. The validation of the simulation methodology is done by comparing the simulated and experimental values of current distribution pattern of an SAPV system. The comparative results of simulation and experiment results match a confidence level of 92%. The proposed regression model was also compared with a real-time example. This model explicitly helps a designer to evaluate the system requirements for given input data within a predefined tolerance. View full abstract»

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  • Dynamic Real-Time I–V Curve Measurement System for Indoor/Outdoor Characterization of Photovoltaic Cells and Modules

    Page(s): 1 - 7
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    A test method that measures the current-voltage I–V curve of a photovoltaic (PV) cell or module in real time is presented as a means of characterizing and understanding the inherently variable nature of performance under field conditions. Temperature, incident light intensity, orientation to the light source, incident spectrum, the uniformity of illumination, as well as a diverse set of failure mechanisms, both catastrophic and otherwise, have characteristic effects on the I–V curve. Seeing the I–V curve change dynamically with these influences allows visual correlation to real-time events. With a live I–V curve generated by performing forward and reversed bias sweeps repeatedly, the effect of parasitic inductance and bias sweep rate on the measurement can be demonstrated directly. This technique also ensures that the device junction is held in quasi-thermal equilibrium during the measurement. The relative alignment of optics in a concentrating photovoltaic module is analyzed to demonstrate the value of the live I–V curve. View full abstract»

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  • New Nanostructured Materials for Efficient Photon Upconversion

    Page(s): 1 - 5
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    Although methods for harvesting subbandgap solar photons have been demonstrated, present approaches still face substantial challenges. We evaluate carrier escape mechanisms in an InAs/GaAs quantum dot (QD) intermediate band photovoltaic (PV) device using photocurrent measurements under subbandgap illumination. We show that subbandgap photons can generate photocurrent through a two-photon absorption process, but that carrier trapping and retrapping limit the overall photocurrent regardless of whether the dominant carrier escape mechanism is optical, tunneling, or thermal. We introduce a new design for an InAs QD-based nanostructured material that can efficiently upconvert two low-energy photons into one high-energy photon. Efficiency is enhanced by intentionally sacrificing a small amount of photon energy to minimize radiative and nonradiative loss. Upconversion PV devices based on this approach separate the absorption of subbandgap photons from the current-harvesting junction, circumventing the carrier-trapping problems. View full abstract»

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  • Enhanced Light Trapping in a-Si:H/μc-Si:H Tandem Solar Cells via Nanopatterning Top Absorber and Embedding Wavelength-Selective Intermediate Reflectors

    Page(s): 1 - 9
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    Output photocurrent of a-Si:H/μc-Si:H tandem solar cells is usually determined by the unsatisfactory absorption of a-Si:H layer restricted by its thin thickness required by the very limited carrier diffusion length and low absorption coefficient at wavelengths over 550 nm. In this paper, we present a new configuration to enhance the light-trapping performance and the output photocurrent of a-Si:H/μc-Si:H tandem solar cells via the nanopatterning a-Si:H layer and embedding wavelength-selective intermediate reflector layer (WSIRL) between the top and bottom cells. Our simulations indicate that absorption and photocurrent of the tandem cells in the proposed scheme exhibit a significant and wide-angle enhancement compared with the planar cases with or without WSIRL and the nanopatterned case without WSIRL. An ultimate photocurrent density, which is obtained under normally incident AM1.5G solar irradiation and ideal internal quantum efficiency, is 37.56% higher than that of the planar counterpart with a normal ZnO intermediate reflector. Moreover, the attenuation ratio of the output photocurrent in the proposed configuration is only 2.95% when the incident angle alters from 0° to 60°. View full abstract»

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  • >23% High-Efficiency Tunnel Oxide Junction Bifacial Solar Cell With Electroplated Cu Gridlines

    Page(s): 1 - 5
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    Based on the metal–insulator–semiconductor concept, Triex cell is a proprietary device structure that combines a tunnel oxide junction with doped a-Si thin-film emitter layers on n-type Czochralski silicon wafers. A simple patterning process is used along with cost-effective copper electrochemical plating to form the electrodes. This paper reports a >23% high-efficiency Triex solar cell, postoptimizing key process areas to improve passivation, junction quality, and shading effects. High open-circuit voltage ($V_{rm oc}$) of 739 mV and good fill factor of 80.5% have been demonstrated on a 6-in solar cell. A champion 380-W Triex bifacial module is also validated under standard test conditions. View full abstract»

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  • Resistive Power Loss Analysis of PV Modules Made From Halved 15.6 × 15.6 cm2 Silicon PERC Solar Cells With Efficiencies up to 20.0%

    Page(s): 1 - 7
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    In photovoltaic (PV) modules, the interconnection of solar cells is critical in terms of mechanical stability and resistive power losses. In this study, we analyze the interconnection of large-area 15.6 × 15.6 cm2 industrial p-type passivated emitter and rear cell (PERC) solar cells in terms of resistive losses. For our analysis, we prepare a 3 × 3 minimodule from PERC solar cells with soldering pads and efficiencies up to 20.0%. We measure a significant cell-to-module (CTM) power loss of 8% at this module. For comparison, we prepare a 3 × 6 module consisting of halved 7.8 × 15.6 cm2 PERC solar cells. Using a nanosecond laser to cut the finished solar cell in two pieces, no additional power loss is introduced by cutting. The CTM factor of 1.0 determined at the 3 × 6 module is explained using an analytical model describing the series resistance of the module interconnection. Using this model, we estimate for our current PERC cell generation and module process an output power of 275 W for 60 full-size cells and 285 W for 120 halved cells. View full abstract»

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  • New Approaches to Improve the Performance of Thin-Film Radial Junction Solar Cells Built Over Silicon Nanowire Arrays

    Page(s): 1 - 6
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    Owing to their enhanced light trapping and antireflection effects, silicon nanowires (SiNWs) provide an active research platform for a new generation of cost-effective and efficient solar cells. By optimizing the density of nanowires and depositing amorphous silicon (a-Si:H) on top of them, stable radial junction p-i-n devices with efficiencies in the range of 8–9% have already been realized, and there is still room for improvement. For instance, by modifying the SiNW/a-Si:H interface, an open-circuit voltage as high as 0.9 V has been achieved. In addition, increasing the bandgap of the window layer is found to be effective for blue-response enhancement. Modeling of equivalent structures with a-Si:H nanowires by rigorous-coupled wave analysis method shows that short-circuit current density can be improved up to 20 mA/cm2, and changing the active material to crystalline silicon allows us to broaden the absorption to near infrared spectral region. Initial results with hydrogenated microcrystalline silicon as an active layer are also presented. View full abstract»

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  • Analysis of the Annual Performance of Bifacial Modules and Optimization Methods

    Page(s): 1 - 9
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    Bifacial modules have the advantage of capturing sunlight from front as well as from rear surfaces, and therefore, they are able to produce larger amounts of energy, compared with standard (monofacial) modules. However, their performance depends on the spatial distribution of the irradiance incident on the rear module surface, which is strongly affected by several site-specific conditions, such as albedo, reflective surface size, module elevation, and tilt angle. In this study, we elaborate upon the individual and combined effects of these factors on the annual energy yield of stand-alone south-facing bifacial modules through simulations at two site locations with contrary climatic conditions. Following the optimization of the tilt angle of bifacial modules dependent on the site, albedo, and module elevation, we demonstrate that the annual energy yield of a bifacial module increases linearly with albedo, which shows a monotonically increasing but, in addition, saturating behavior versus reflective surface size, and increases up to a certain module elevation. Through the simultaneous consideration of these dependences, we suggest an optimal positioning of bifacial modules. Finally, we show that under these optimal conditions, bifacial modules can supply up to 25% more energy compared with standard modules. View full abstract»

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  • Harmonically Modulated Luminescence: Bridging Gaps in Carrier Lifetime Metrology Across the PV Processing Chain

    Page(s): 1 - 7
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    Carrier lifetime measurements via harmonically modulated luminescence have considerably evolved recently, giving rise to numerous relevant advances and applications in materials science. An essential asset of this technique lies in its unified applicability across the photovoltaic processing chain—from ingots to solar cells. This paper shows how present gaps in carrier lifetime metrology are overcome via harmonically modulated luminescence by focusing on the complete theoretical understanding of harmonically modulated lifetime, on its unmatched bulk lifetime contrast for silicon ingots, and on the capability to monitor the metalization process. Practical considerations for a straightforward (and spatially resolved) ingot bulk lifetime extraction via harmonically modulated luminescence are detailed and validated. Example lifetime investigations demonstrate this technique’s capability of bridging the addressed conceptual and instrumental gaps. View full abstract»

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  • Determination of Dominant Failure Modes Using FMECA on the Field Deployed c-Si Modules Under Hot-Dry Desert Climate

    Page(s): 1 - 9
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    The failure and degradation modes of about 5900 crystalline-Si glass/polymer modules fielded for six to 16 years in three different photovoltaic (PV) power plants with different mounting systems under the hot-dry desert climate of Arizona are evaluated. Based on the results of this evaluation, failure mode, effect, and criticality analysis, a statistical reliability tool that uses risk priority number is performed for each PV power plant to determine the dominant failure modes in the modules by means of ranking and prioritizing the modes. This study on PV power plants considers all the failure and degradation modes from both safety and performance perspectives and, thus, comes to the conclusion that solder bond fatigue/failure with/without gridline contact fatigue/failure is the most dominant failure/degradation mode for these module types in the hot-dry desert climate of Arizona. View full abstract»

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  • Interlaboratory Study to Determine Repeatability of the Damp-Heat Test Method for Potential-Induced Degradation and Polarization in Crystalline Silicon Photovoltaic Modules

    Page(s): 1 - 8
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3279 KB)  

    To test reproducibility of a technical specification under development for potential-induced degradation (PID) and polarization, three crystalline silicon module types were distributed in five replicas each to five laboratories. Stress tests were performed in environmental chambers at 60 °C, 85% relative humidity, 96 h, and with module nameplate system voltage applied. Results from the modules tested indicate that the test protocol can discern susceptibility to PID according to the pass/fail criteria with acceptable consistency from lab to lab; however, areas for improvement are indicated to achieve better uniformity in temperature and humidity on the module surfaces. In the analysis of variance of the results, 6% of the variance was attributed to laboratory influence, 34% to module design, and 60% to variability in test results within a given design. Testing with the additional factor of illumination with ultraviolet light slowed or arrested the degradation. Testing at 25 °C with aluminum foil as the module ground was also examined for comparison. The foil, as tested, did not itself achieve consistent contact to ground at all surfaces, but methods to ensure more consistent grounding were found and proposed. The rates of degradation in each test are compared, and details affecting the rates are discussed. View full abstract»

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  • NH$_{bf 4}$Cl Alternative to the CdCl$_{bf 2}$ Treatment Step for CdTe Thin-Film Solar Cells

    Page(s): 1 - 4
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    The CdCl$_2$ treatment is a key step in CdTe solar cell fabrication. However, despite its near ubiquitous use, the process is nonideal as CdCl$_2$ is both expensive and potentially hazardous to utilize in processing. In this paper, we report on the development of a NH$_4$Cl replacement to the CdCl$_2$ process, which is a low-cost noncarcinogenic alternative. Comparative cells were fabricated and compared via C–V, J–V, scanning electron microscopy, and external quantum efficiency analysis. Further process optimization led to device efficiencies of up to 11.5%, achieved using this new process, with V$_OC$ values of up to 832 mV, which is relatively high. View full abstract»

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  • Prevention of Potential-Induced Degradation With Thin Ionomer Film

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (586 KB)  

    Significant power loss has been observed in photovoltaic (PV) modules resulting from high voltage bias experienced in the field. This type of failure has been called potential-induced degradation (PID). Encapsulant materials provide protection and electrical isolation of the solar components in PV modules. Several researchers have shown that the type of encapsulant can directly affect the severity of the PID. Ionomers, in particular, were amongst the first encapsulants identified as having the ability to prevent this degradation mechanism. In this study, we introduce an ionomer/EVA bilayer encapsulant to the module to determine the effect of ionomer on PID and sodium ion migration in mini- modules. We determined that the encapsulant’s volume resistivity is temperature independent with the presence of ionomer. Results confirm that the module's volume resistivity at elevated temperature inversely correlates with leakage current and that ion enrichment at the cell/encapsulant interface correlates with power degradation of a PV module. The rate of sodium ion migration to the cell was also investigated. An analytical method was refined for this application using laser ablation and mass spectrometry to observe the sodium migration within the module. Sodium ion profiles were obtained by elemental mapping of the encapsulant and solar cell cross section after the module had been exposed to a simulated PID test. Results show that sodium ion accumulation at the encapsulant/solar cell region increases linearly with PID testing time when only EVA encapsulant is used and is significantly different when an ionomer/EVA encapsulant is used in the module. View full abstract»

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  • Diffusion and Segregation Model for the Annealing of Silicon Solar Cells Implanted With Phosphorus

    Page(s): 1 - 8
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    We present a fully calibrated model for the diffusion, segregation, and activation of phosphorus for typical annealing conditions of implanted silicon solar cells. In contrast to existing process simulation software, this model allows the quantitative prediction of doping profile distributions, and, thereby, sheet resistances, surface concentrations, and junction depths. The model also provides an intuitive understanding of the dependence of these quantities on the parameters of the annealing process. View full abstract»

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  • Evidence for Vacancy-Related Recombination Active Defects in as-Grown N-Type Czochralski Silicon

    Page(s): 1 - 6
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    A recombination of active defect in very high lifetime Czochralski grown n-type silicon wafers, which can be thermally deactivated at 150 °C, is described. In addition, the existence of a recently measured defect, which is deactivated at 350 °C, is confirmed. Both defects are found to significantly degrade the lifetime of millisecond-range Czochralski-grown n-type silicon wafers: a material widely used for high-efficiency solar cells. The observed deactivation temperature suggests that it may be caused by vacancy-phosphorus pairs. The deactivation temperature of the second defect is consistent with the presence of vacancy-oxygen (V-O) pairs. View full abstract»

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  • Investigations on Al$_{bm x}$Ga$_{bm {1-x}}$As Solar Cells Grown by MOVPE

    Page(s): 1 - 8
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    Solar cells based on Al$_{x}$Ga$_{1-x}$As in its direct bandgap range were fabricated and analyzed. We show that state-of-the-art metalorganic vapor phase epitaxy systems and precursors are capable of growing Al$_{x}$Ga$_{1-x}$As solar cells with defect concentrations up to 1 × 1014 cm−3 and less determined by deep level transient spectroscopy. However, for the n-doped material, inevitable DX-centers exist. These dopant-related defects limit the performance of the investigated Al$_{x}$Ga$_{1-x}$As solar cells with x ≥ 0.20. To overcome this issue, the n-doped Al$_{x}$Ga$_{1-x}$As emitter can be replaced by an n-doped Ga$_0.51$In$_0.49$P heteroemitter. This heterojunction solar cell again shows overall defect concentrations below 1 × 1014 $hbox{cm}^{-3}$ and significantly improved cell characteristics. View full abstract»

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Aims & Scope

The IEEE Journal of Photovoltaics is a peer-reviewed, archival publication reporting original and significant research results that advance the field of photovoltaics (PV).

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Meet Our Editors

Editor-in-Chief
Timothy J. Anderson
Chemical Engineering Department
University of Florida