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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Multi-channel front-end ASIC for a 3D position-sensitive detector

Arrays of 3D position-sensitive detectors (3DPSD), operating at room temperature and using cadmium zinc telluride (CZT) and thallium bromide (TIBr) sensors, are suitable for gamma-ray spectrometry in many applications. One detector configuration, the 3D position-sensitive Virtual Frisch-Grid detector (VFG), is particularly advantageous for integrating into large area arrays. The signals generated inside each detector of the array are captured with the anode, cathode and four pads that enable the reconstruction of the position and energy of the ionizing interaction by measurements of amplitude and timing of the signals. For these applications, a low-noise front-end ASIC has been developed, capable of processing bipolar signals (needed because of AC-coupling of certain electrodes). The ASIC can be coupled to an ADC in order to form a compound “waveform digitizer” capable of post-processing the analog signals and determining amplitude and timing information. This paper describes a 32-channel front-end ASIC that is suitable for reading out a 3 × 3 or 4 × 4 element matrix in the VFG configuration. Each channel is composed of a low-noise charge amplifier with an adaptive continuous reset feedback circuit suitable for both positive and negative charge, a first order shaper and a single-to-differential converter output stage. Voltage and current references are all internally generated by 10-bit DACs and the chip is fully controllable with the I 2 C communication protocol. The readout channel response has been verified using the implemented injection circuit. Linear behavior up to ~75 ke ± with the gain of ~80 mV/fC, and up to ~200 ke ± with the gain of ~30 mV/fC was demonstrated. In conclusion, the first test result waveforms using a 137 Cs radioactive source on a 5 × 5 × 12 mm 3 TIBr crystal are reported.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Resilience of High-Efficiency CdSeTe:As and CdSeTe:Cu Solar Cells to Proton Irradiation

Power generation in space is currently dominated by expensive III-V multi-junction photovoltaic (PV) devices and cheap crystalline silicon (c-Si) PV devices. Both of these technologies degrade rapidly in proton-radiation-rich space environments, such as the Van Allen belt. The present study of cadmium selenide telluride- (CdSeTe-) based PV devices exposed to 150-to-1500 keV proton irradiation with fluences up to 9 x 1013 cm-2 reveal a more radiation-hard alternative to III-V and c-Si PV technologies. We report on measurement and analysis of current density vs voltage (JV), external quantum efficiency (EQE), external radiative efficiency, and capacitance vs voltage (CV) characteristics. JV characteristics of As-doped CdSeTe devices show 80% remaining power conversion efficiency (PCE) relative to unexposed controls when exposed to 650 keV protons at a fluence of 1012 cm-2. Under these same irradiation conditions, Cu-doped CdSeTe devices demonstrate an even better 95% PCE retention compared with unirradiated control devices. Evidence of radiation-induced absorber p-type doping compensation is observed in the glass-side EQE at 0 V and CV characteristics of most of the irradiated CdSeTe:As devices, but clear compensation is evident only for the most heavily irradiated CdSeTe:Cu devices. Elevated blue-green photocurrent in the film-side 0 V EQE suggests a buried junction in the most heavily irradiated CdSeTe:As devices. Although CdSeTe:Cu devices are the more resilient of the CdSeTe structures, both CdSeTe-based technologies are radiation-hard when compared to c-Si and III-V multi-junction PV.

14 SOLAR ENERGY↗
DOE OSTI2021

Charge Transport and Space-Charge Formation in Cd 1 - x Zn x Te 1 - y Se y Radiation Detectors

The electron- and hole-transport properties in cadmium zinc telluride selenide (CZTS) crystals are studied using a laser-induced transient-current technique with pulsed and dc bias. The internal electric field profile and velocity of surface recombination are determined by Monte Carlo simulations of electron and hole transient currents combined with a numerical solution of the drift-diffusion equation coupled with Poisson’s equation. Electron and hole drift mobilities of μe = 830 cm 2 /Vs and μh = 40 cm 2 /Vs, respectively, are determined. We also develop a simple technique for evaluating surface recombination directly from measured current waveforms without the need for numerical simulation. The good quality of the prepared detector at pulsed bias, with electron- and hole-mobility-lifetime products of (μτ)e = 1.9 × 10 -3 cm 2 /V and (μτ)h = 1.4 × 10 -4 cm 2 /V, respectively, are observed. The formation of a positive space charge, originating from hole injection combined with a recombination level, is found. We observe a significant position dependence of the lifetime of electrons and holes in dc bias due to hole injection. The experiment is successfully fitted by a simple model dominated by a single deep recombination level with an energy of E t =E C -0.73eV; concentration of 7.3 × 10 11 cm -3 ; and electron- and hole-capture cross sections of 3.5 × 10 -14 cm 2 and 6.5 × 10 -14 cm 2 , respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Characterizing electron-collecting CdTe for use in a 77 ns burst-rate imager

The Keck-PAD (pixel array detector) was developed at Cornell as a burst-rate imager capable of recording images from successive electron bunches (153 ns period) from the Advanced Photon Source (APS). Both Si and hole-collecting Schottky CdTe have been successfully bonded to this ASIC (application-specific integrated circuit) and used with this frame rate. The facility upgrades at the APS will lower the bunch period to 77 ns, which will require modifications to the Keck-PAD electronics to image properly at this reduced period. In addition, operation at high X-ray energies will require a different sensor material having a shorter charge collection time. For the target energy of 40 keV for this project, simulations have shown that electron-collecting CdTe should allow >90% charge collection within 35 ns. This collection time will be sufficient to sample the signal from one frame and prepare for the next. 750 µm-thick electron-collecting Schottky CdTe has been obtained from Acrorad and bonded to two different charge-integrating ASICs developed at Cornell, the Keck-PAD and the CU-APS-PAD. Carrier mobility has been investigated using the detector response to single X-ray bunches at the Cornell High Energy Synchrotron Source and to a pulsed optical laser. The tests indicate that the collection time will meet the requirements for 77 ns imaging.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Combinatorial Study of MZO Emitters for CdTe-Based Solar Cells

Precise band alignment at the front interface of CdTe-based solar cells is necessary to reduce photoexcited charge carrier recombination and to enable higher energy conversion efficiencies. Magnesium zinc oxide is not only transparent but also offers the ability to tune the conduction band offset with CdTe at the front of the device stack. In this work, we describe reactive sputtering of Mg 1-x Zn x O using metal targets and its application in CdTe photovoltaics. Combinatorial libraries of Mg 1-x Zn x O were created to tune the conduction band alignment for the optimal performance of CdTe solar cells. Band gap variation of more than 0.4 eV is achieved across a 3-inch substrate. Kelvin probe measurements demonstrate variance of work function across the substrate. Device performance is optimized at band gaps of 3.5 eV for the CdTe device processing conditions employed in this study.

14 SOLAR ENERGY↗
DOE OSTI2020

Spatially and Spectrally Resolved Defects in Polycrystalline CdTe Thin Films Revealed by Quantitative Cathodoluminescence

Increasing the grain size is a potential strategy to reduce grain-boundary recombination and improve performance of thin-film solar cells. Here, CdTe thin films with a range of grain sized were produced by varying the CdC1 2 post-deposition treatment temperature. We use high-resolution cathodoluminescence (CL) microscopy to study recombination and shallow defect levels in detail. Intensities from room temperature CL maps were compared across samples. We find that the CL intensity initially increases with grain size, as expected, but then plateaus as the grain size is increased further. The plateau is correlated with a decrease in the characteristic length-related to the carrier diffusion length-determined from CL intensity profiles near grain boundaries. In addition, low-temperature CL measurements demonstrate the evolution of the defect levels with CdC1 2 temperature.

cadmium telluride thin films↗
DOE OSTI2021

Quantifying Bulk and Surface Recombination in CdTe Solar Cells Using Time-Resolved Terahertz Spectroscopy

Understanding the nature of recombination mechanisms is essential for higher power conversion efficiency in photovoltaic (PV) devices. Here we use a combination of time-resolved terahertz spectroscopy and numerical modeling to determine the bulk Shockley-Read-Hall lifetime and interface and back surface recombination velocities in CdTe thin film stacks. Furthermore, the measurement was facilitated by fabricating wire-grid device structures using conventional laser scribing. Evaluation of a glass/FTO/SnO2/CdS/CdTe stack treated with CdCl2 allowed separation of the CdTe absorber bulk lifetime, 1.6 ns, from the back surface recombination velocity, ~6x10 4 cm/s, and indicated that CdTe/CdS interface recombination velocity had no significant impact on carrier dynamics.

14 SOLAR ENERGY↗
DOE OSTI2021

Carrier Lifetime as a Function of Se Content for CdSexTe1-x Films Grown on Al2O3 and MgZnO

Time-resolved photoluminescence (TRPL) with two excitation wavelengths – 670 (standard) and 405 nm – was used to examine the effect on carrier lifetime of two significant recent advances in CdTe: the incorporation of Se to form graded CdSe x Te 1-x and the use of Mg y Zn 1-y O buffers. The two excitation wavelengths probe depths of approximately 130 and 35 nm, respectively, and their comparison helps differentiate interface and bulk contributions to carrier lifetime. It was found that x = 0.2 Se was required to obtain lifetime improvements, primarily in the bulk. Additionally, TRPL traces for Mg y Zn 1-y O/CdSe x Te 1-x samples showed fast initial decay followed by a long-lived tail, which may be indicative of trap-dominated recombination. This behavior was not present for CdSe x Te 1-x films grown on Al 2 O 3 , which is currently state-of-the-art for surface passivation in CdTe. This indicates that further work is required to sufficiently passivate the front interface.

cadmium telluride↗
DOE OSTI2022

Effect of Near-Interface Compensation of CdSeTe Absorber Layers on Solar Cell Performance

Arsenic has been shown to be an effective p-type dopant of CdTe. However, challenges remain in the fabrication of high efficiency CdTe solar cells using As. As-doped CdTe is prone to self-compensation and observed accumulation of dopant atoms in CdTe near the interface with MgZnO (MZO) suggests that this could be occurring. In this study, we use SCAPS 1-D modeling software to investigate the effect of near-interface compensation. We consider three cases: shallow donors, deep recombination centers, and a thin layer of excess positive charge accumulation. All of these cases are shown to have significant effects on the current-voltage characteristics, while the thin charge layer also affects capacitance-voltage measurements.

arsenic↗
DOE OSTI2020

Gamma Equipment System Requirements by Application

This document outlines a set of requirements for gamma sensitive systems applied to three different applications: (1) homeland security (search and identification); (2) in-situ quantification; and (3) quantification in a material characterization laboratory. These three applications represent a range of activities that a country might use for locating, identifying, and quantifying radioactive material. These applications require increasing accuracy and system advancements, and skill levels. This document considers systems with various detector types and are characterized by their energy resolution: (1) low resolution (e.g., NaI(Tl) scintillation) and (2) higher resolution (e.g., high-purity germanium [HPGe] solid state) systems. The higher resolution systems also include cadmium zinc telluride (CZT) and only mechanically cooled HPGe systems are considered. These detectors and their associated acquisition hardware and analysis software afford a broad range of capabilities with corresponding ranges of complexity, maintainability, and cost. Ultimately, the equipment must meet the measurement goals of the application, and compliance with a given list of hardware specifications does not in itself guarantee meeting those goals. Examples of typical performance objectives for international safeguards applications are documented in International Target Values 2010 for Measurement Uncertainties in Safeguarding Nuclear Materials (IAEA, STR-368, November 2010). Selection of the detector type best suited to a specific application is often a compromise between “state of the art” or best available option and what is practical.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

24.1.3.1.1 - Frisch Grid CZT Spectrometer

Brookhaven National Laboratory (BNL) worked with FLIR System Inc., the manufacturer of the nanoRAIDER, to develop a handheld field deployable detector based on the novel position-sensitive virtual Frisch-grid (VFG) Cadmium-Zinc-Telluride (CdZnTe or CZT) detectors (with 1% FWHM at 662 keV or better energy resolution). The detector called nanoRAIDER-VFG would be an improvement to the current nanoRAIDER, which is a compact gamma-ray detection instrument manufactured by FLIR Systems Inc. that employs relatively lower-performing CZT hemispheric detectors (i.e., 3%-FWHM CZT detectors). The nanoRAIDER-VFG would have significantly improved accuracy of measurements while maintaining similar efficiency, as compared to the nanoRAIDER, for in-field analysis of nuclear materials and detection of undeclared activities during inspections conducted by the International Atomic Energy Agency (IAEA). Since the nanoRAIDER is currently used by the IAEA as part of its Complementary Access toolkit, a relatively quick acceptance of the nanoRAIDER-VFG for safeguards was anticipated. The nanoRAIDER-VFG project was undertaken to address the following items in the IAEA's Long-Term R&D Plan, 2012-2023: 2.2 (elemental and isotopic signatures of fuel cycle processes); 2.3 (detect signatures of undeclared activity and improve analysis); and 2.6 (detect process emanations). The high energy-resolution of the nanoRAIDER-VFG would also have had applicability to 3.2 (fissile content of metal mixtures containing actinides Np, Am, etc.). The project was not completed due to a change in priorities within FLIR.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Solar Photovoltaic (PV) Manufacturing Expansions in the United States, 2017-2019: Motives, Challenges, Opportunities, and Policy Context

This report analyzes U.S. PV manufacturing announcements from 2017 through July-2019 and explores the potential impact of tariffs on the competitiveness of U.S. PV module manufacturing. First, the fraction of announcements that resulted in established facilities in the time frame specified is analyzed, as well as firm nationality and the existence of any other U.S. facilities for the firm. The prevalence of different PV product types among the announcements was also analyzed, as well as the type of facilities selected for development (greenfield, existing PV factories, or repurposed buildings). The cost to build these facilities was also analyzed in the context of their capacity, the value of incentives received by state and local governments, and the number of jobs created. Case studies of Auxin Solar, First Solar, Hanwha Q Cells, JinkoSolar, LG, Silfab, Solaria, and SunPower were conducted and highlight five factors influencing firms’ decisions to expand their U.S. PV production capacity. These included: 1) proximity to demand, including supply contracts and demand for domestic content 2) tariffs and other incentives. The Section 201 tariffs on PV module imports were often described helpful but tariffs on cell imports (Section 201) or materials (Section 301, Section 232) were often described as counterproductive since U.S. supply chains do not exist for many necessary goods. The corporate tax decrease and local incentives were often mentioned as helpful. 3) the ability to move quickly in order to maximize the benefit of the Section 201 tariffs. This affected decisions to select localities with faster permitting or moving into existing buildings. 4) competition with scale, where competing with Asian PV imports or avoiding imports of material from China was challenging due to the larger scale of Asian manufacturers. Additionally, smaller firms expressed concerns that larger firms may not need their U.S. facilities to profitable. 5) access to capital, which was a particular challenge for smaller firms. Several U.S. tariffs affect the economics of PV cells, modules, and balance-of-module (BOM) materials, some of which are applicable to a long list of countries and others applicable only to China or Taiwan. We analyze how the tariffs interact to affect the prices of c-Si modules sourced under various assumptions about domestic and imported components and assembly. We estimate module prices under a range of baseline scenarios featuring U.S.-assembled modules with Southeast Asian cells (not from China or Taiwan). When all BOM components are sourced from the United States, baseline module prices are $0.37/W (below the 2.5-GW Section 201 cell cap) to $0.42/W (above the 2.5-GW cell cap). If all BOM components are sourced from China, the module price in this baseline U.S.-assembly scenario can reach up to $0.60/W. Imported module prices are lower than or within the range of the U.S.-assembled baseline prices under some conditions. Importing bifacial modules from Southeast Asia is the lowest-priced alternative, at $0.35/W, because bifacial modules are excluded from the Section 201 tariffs. Importing Southeast Asia modules that contain U.S. cells results in a price of $0.38/W, also owing to a Section 201 exclusion. Importing Southeast Asian modules that have Southeast Asian cells yields a price of $0.44/W, and importing Chinese modules that have U.S. cells yields a price of $0.58/W. These results suggest that U.S. tariff policy in 2019 may encourage U.S. assembly of mono-facial c-Si modules if the 2.5-GW cell import cap is not reached and Chinese BOM imports are negligible. However, some imported module options may offer the lowest prices if the 2.5-GW cell import cap is reached and/or U.S. module manufacturers must rely on significant Chinese BOM content. The analysis shows the 2.5-GW cell cap may be exceeded in 2019 and following years. It is also likely that U.S. module manufacturers will need to use at least some Chinese BOM content, since U.S. module manufacturers have stated that U.S. supply chains do not exist (or do not exist at a sufficient scale) for most BOM components, which makes them at least partially reliant on Chinese BOM and thus subject to Section 301 tariffs.

14 SOLAR ENERGY↗
DOE OSTI2021

Photovoltaics Research and Development: Device Architecture for Next-Generation CdTe PV. Cooperative Research and Development Final Report, CRADA Number CRD-17-00662

Despite remarkable efficiency improvements at the cell and module level, thin-film CdTe PV suffers from a significant voltage deficit compared with the ideal. The proposed solution is to build cells with fully depleted absorbers and with energy barriers front and back to direct electrons and holes in appropriate directions. Combined with minimal interfacial recombination, this approach, which is similar to the successful silicon HIT cells, circumvents the need for higher lifetimes and carrier concentration to achieve higher voltage, Colorado State is particularly well-positioned to the address the depleted absorbed architecture. It has robust single-vacuum closed-spaced-sublimation deposition chamber, currently being enhanced with new sources for CdTe alloys and grading. It has made reasonable-efficiency cells with absorbers as thin as 0.3 um, it has demonstrated electron reflection at the rear of the absorber with a continuous CdMgTe layer, it has replaced CdS with MgZnO, which has several advantages including tunable band offsets, and it has achieved 16.8% efficiency. It also has a mature suite of measurement equipment for cell evaluation and the experience to effectively analyze its results for refinement in cell fabrication. Several healthy collaborations will continue within the CdTe community.

14 SOLAR ENERGY↗
DOE OSTI2021

Gamma spectrometry uranium isotopic analysis rodeo: Summary of GADRAS results

This report summarizes GADRAS methods and gamma spectrometry rodeo uranium isotopic analysis results for high energy resolution H3D M400 cadmium zinc telluride (CZT) and ORTEC Micro Detective high-purity germanium (HPGe) spectra of uranium isotopic standards collected at Oak Ridge National Laboratory (ORNL) and Lawrence Livermore National Laboratory (LLNL) over a two-year measurement campaign. During the campaign, measurements were performed with the detectors unshielded, side shielded, and collimated. In addition, measurements of the uranium isotopic standards were performed unshielded and shielded.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2022

Study of charge trapping in CZT detectors

A semiconductor detection material, Cadmium Zinc Telluride, was investigated for potential use as a particle detector for space flight applications. Our set of detectors was determined to be flawed for particle detection methods, likely due to charge transport mechanisms within the detector material, or due to reduced voltage required to avoid dielectric breakdown. It was observed that the method of crystal growth may play a role in the performance, but performance may also vary between manufacturers using the same growth method. It is recommended to perform further study at a larger proton beam facility.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Cross-Cutting Metrology Tools for In Operando Characterization of Carrier Dynamics in Photovoltaic Devices (Final Technical Report)

Understanding the nature of recombination and its dependence on defects and interfaces is essential for engineering materials and contacts for higher V oc and photovoltaic (PV) efficiency. Time-resolved photoluminescence (TRPL) has conventionally been used to evaluate recombination, but not all materials are strongly emissive or otherwise suitable. Time-resolved terahertz spectroscopy is a pump – probe method that presents valuable complementary information, wherein an optical pump pulse photoexcites carriers within the absorber and the transient photoconductivity is probed with a terahertz pulse. Until now, experimental constraints have prohibited the use of terahertz probes to interrogate full device stacks, and measurements were instead made on exfoliated films or films grown on unconventional substrates. However, interfaces are critical to the behavior of photoexcited carriers in solar cells, and the substrates themselves often influence the film growth and bulk properties. Therefore, it is important to probe the behavior of PV absorbers as close as possible to their normal operating conditions. Here we have developed cross-cutting metrology that enable in operando characterization of carrier dynamics and recombination mechanisms in working PV devices. Through a combination of complementary non-contact TRTS and TRPL experiments and modeling, we have obtained key parameters including photoexcited carrier bulk lifetime and interface and back surface recombination velocities with greater precision and accuracy than can be achieved with conventional TRPL alone. By varying pulsed photoexcitation conditions, the contributions of interface and bulk recombination mechanisms can be determined. We have developed and refined this characterization approach by investigating CdTe PVs, which is a well-established technology but with significant margin for further improvements in efficiency. Results were published in Journal of Applied Physics (DOI: 10.1063/5.0064730) and Proceedings of the IEEE PVSC (DOI: 10.1109/PVSC43889.2021.9518559). After validating the approach, we have applied it to correlate recombination rates to processing conditions and material properties, including composition and defects as well as interfaces and surface treatments. Such feedback can inform processing and design choices to enable higher PV efficiency, not only for CdTe, but also CdSe x Te 1-x , CIGS, perovskites, kesterites, and future technologies. A perspective on predicting solar cell performance from terahertz spectroscopy was published in Advanced Energy Materials (DOI: 10.1002/aenm.202102776). The cross-cutting metrology tools developed here will enable determination of the locus and mechanism of performance-limiting recombination in thin film PV devices. This feedback can guide the engineering of PV devices with higher V oc and efficiency, thereby leading to reductions in levelized cost of electricity to meet the SunShot 2030 target of $0.03/kWh for utility-scale PV. Lower costs will enable rapid expansion of renewable electricity generation that is nearly free of carbon emissions. Reducing carbon emissions of the electricity sector is one of the most important solutions to climate change. The project’s specific focus on CdTe PV can benefit First Solar, the US company that is the global leader in CdTe technology, through both technology and workforce development.

14 SOLAR ENERGY↗
DOE OSTI2023

Collaborative R&D with First Solar on Understanding Performance Limitations in CdTe (Project 1 "CdTe" - Mods 0-10, 13, 14-A1, 17)

This CRADA involves analyses on a variety of CdTe and CdTe-PV related materials, test structures, and solar cells produced at FSLR or NREL. Single-crystal (sx) material will be primarily MBE grown and provided by FSLR. Joint activities are focused on establishing the appropriate quality metrics as a basis for high performing sx devices and to study the dopability of the material. Polycrystalline (px) materials will be provided by NREL, FSLR, or fabricated jointly. Px activities are focused on the characterization of performance limiting mechanisms including bulk defects, grain boundaries, and the hetero-interface. A combination of growth, characterization, and theory will be applied. Analysis will include techniques that are well established in CdTe research at NREL (e.g., LIV/DIV/CV, AS/DLTS, LTPL, TRPL) as well as techniques that have not been widely applied to the PV part of CdTe technology (e.g., PCD, CL, uPL, SE).

14 SOLAR ENERGY↗
DOE OSTI2024

Diagnosing and overcoming recombination and resistive losses in non-silicon solar cells using a silicon-inspired characterization platform

This project aimed to generate the characterization tools needed for accurate and systematic loss analysis in non-silicon photovoltaic solar cell technologies and, through the use of these tools and analysis techniques, contribute to the development of a novel class of hetero-contacts to II-VI absorbers, with the final goal of demonstrating record-breaking CdSeTe devices. CdSeTe solar cells provide a prime example of the potential impact of the techniques we proposed to develop and implement: record poly-CdSeTe cells have bandgap-voltage deficits (W oc ) of approximately 550 mV, as compared with below 400 mV for all other mature PV technologies. Similarly, these record CdSeTe devices have FFs below 80%, when other mature cells are near or above 85%. Frustratingly, a systematic identification of the origin of these sub-par performances—for example recombination or resistive losses—has been lacking, thus slowing down the development of these technologies. Similarly, it is often asserted that CdSeTe cells need a better back (hole) contact. Although most believe this is true, no one knew—at the start of this project—how high the V oc and FF could be for a given cell if it had a perfect back contact. Such characterization techniques and loss analysis methods exist and are routinely performed on c-Si solar cells (e.g. injection-dependent lifetime, Suns-V oc , transfer length method, etc). Over the years, they have been instrumental in the development of silicon devices that operate at 91% of their theoretical (Auger) limit. Lifetime testing, and the associated reconstruction of the implied-J-V curve, can moreover be performed at every cell-processing step, thus allowing a direct peek into the impact of that step on cell performance. Therefore, adapting these techniques and tools to non-Si devices would greatly improve their learning rate. In this project, we developed a Suns-ERE technique—the equipment, methodology, and know-how—to measure the implied-J-V curve, the pseudo-J-V curve, and the actual J-V curve of a thin-film solar cell, allowing an accurate assessment of the quality of the bulk material and its surface passivation, the selectivity of the contact, and its resistivity. We used this technique to show that the absorber of present CdSeTe solar cells is capable of achieving 1 V Voc,, that passivation layers exist (e.g., Al2O3) that can support such high voltages, and that the barrier is identifying contact layers that are both passivating and carrier-selective. The characterization platform created in this project and the understanding generated using it will accelerate the progress of non-silicon PV technologies. In particular, the project will contribute to CdSeTe solar cells with Voc > 1 V and cell efficiency > 24%. Such cells provide a pathway to module-level efficiencies >23%. As CdSeTe presently competes with silicon on module cost (in $\$ $/W) and yet has significantly more room for efficiency gains, the potential for LCOE reduction is particularly large. For example, CdTe modules with an efficiency of 21% would allow an LCOE below $\$ $0.04kWh -1 in average US climates.

14 SOLAR ENERGY↗