skip to main content
Explore Scholarly Publications and Datasets in the NSF-PAR

  • NSF Public Access
  • Search Results
  • Accepted Manuscript: Photovoltaic Response of Thin-Film CdTe Solar Cells under Accelerated Neutron Radiation in a TRIGA Reactor
Title: Photovoltaic Response of Thin-Film CdTe Solar Cells under Accelerated Neutron Radiation in a TRIGA Reactor
Cadmium telluride (CdTe) solar cells are a promising photovoltaic (PV) technology for producing power in space owing to their high-efficiency (> 22.1 %), potential for specific power, and cost-effective manufacturing processes. In contrast to traditional space PVs, the high-Z (atomic number) CdTe absorbers can be intrinsically robust under extreme space radiation, offering long-term stability. Despite these advantages, the performance assessment of CdTe solar cells under high-energy particle irradiation (e.g., photons, neutrons, charged particles) is limited in the literature, and their stability is not comprehensively studied. In this work, we present the PV response of n-CdS / p-CdTe PVs under accelerated neutron irradiation. We measure PV properties of the devices at different neutron/photon doses. The equivalent dose deposited in the CdTe samples is simulated with deterministic and Monte Carlo radiation transport methods. Thin-film CdTe solar cells were synthesized on a fluorine-doped tin oxide (FTO) coated glass substrate (≈ 4 cm × 4 cm). CdS:O (≈ 100 nm) was reactively RF sputtered in an oxygen/argon ambient followed by a close-spaced sublimation deposition of CdTe (≈ 3.5 μm) in an oxygen/helium ambient. The sample was exposed to a 10 min vapor CdCl2 in oxygen/helium ambient at 430˚C. The samples were exposed to a wet more » CuCl2 solution prior to anneal 200ºC. A gold back-contact was formed on CdTe via thermal evaporation. The final sample contains 16 CdTe devices. For neutron irradiation, we cleaved the CdTe substrate into four samples and exposed two samples to ≈ 90 kW reactor power neutron radiation for 5.5 hours and 8.2 hours, respectively, in our TRIGA (Training, Research, Isotopes, General Atomics) reactor. We observed a noticeable color change of the glass substrates to brown after the neutron/gamma reactor exposure. Presumably, the injected high-energy neutrons caused the breaking of chemical bonds and the displacement of atoms in the glass substrates, creating point defects and color centers. The I-V characteristics showed noticeable deterioration with over 8 hour radiations. Specifically, the saturation current of the control devices was ≈ 25 nA increasing to 1 μA and 10 μA for the 5.5-hour and 8.2-hour radiated samples, respectively. The turn-on voltage of the control devices (≈ 0.85 V) decreased with the irradiated sample (≈ 0.75 V for 5.5-hour and ≈ 0.5 V for 8.2-hour exposures), implying noticeable radiation damage occurred at the heterojunction. The higher values of the ideality factor for irradiated devices (n > 2.2) compared to that of the control devices (n ≈ 1.3) also support the deterioration of the p-n junction. We observed the notable decrease in shunt resistance (RSH) and the increase in series resistance (Rs) with the neutron dose. It is possible that Cu ions introduced during the CuCl2 treatment may migrate into CdTe grain boundaries (GBs). The presence of Cu ions at GBs can create additional leakage paths for photocarrier transport, deteriorating the overall PV performance. We estimated the radiation dose of CdTe in comparison to Si (conventional PV) using a UUTR model (e.g., MCNP6 2D UTR Reactor simulations). In this model, we simulated Si and CdTe at the center point of the triangular fuel lattice and used an “unperturbed flux” tally in the water. Our simulations yielded a dose rate of 6916 Gy/s of neutrons and 16 Gy/s of photons for CdTe, and 1 Gy/s of neutrons and 21 Gy/s of photons for Si (doses +/- <1%). The large dose rate of neutrons in CdTe is mainly attributed to the large thermal neutron absorption cross-section of 113Cd. Based on this estimation, we calculate that the exposure of our CdTe PVs is equivalent to several million years in LEO (Low-Earth Orbit), or about 10,000 years for Si in LEO. Currently, we are working on a low-dose neutron/photon radiation on CdTe PVs and their light I-Vs and microstructural characterizations to gain better understanding on the degradation of CdTe PVs. « less
Authors:
; ; ; ; ; ; ; ;
Award ID(s):
1711885
Publication Date:
NSF-PAR ID:
10169721
Journal Name:
Electronic Materials Symposium
ISSN:
2434-3471
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ( , Metabolites)
    The acute radiation syndrome is defined in large part by radiation injury in the hematopoietic and gastrointestinal (GI) systems. To identify new pathways involved in radiation-induced GI injury, this study assessed dose- and time-dependent changes in plasma metabolites in a nonhuman primate model of whole abdominal irradiation. Male and female adult Rhesus monkeys were exposed to 6 MV photons to the abdomen at doses ranging between 8 and 14 Gy. At time points from 1 to 60 days after irradiation, plasma samples were collected and subjected to untargeted metabolomics. With the limited sample size of females, different discovery times aftermore »irradiation between males and females were observed in metabolomics pattern. Detailed analyses are restricted to only males for the discovery power. Radiation caused an increase in fatty acid oxidation and circulating levels of corticosteroids which may be an indication of physiological stress, and amino acids, indicative of a cellular repair response. The largest changes were observed at days 9 and 10 post-irradiation, with most returning to baseline at day 30. In addition, dysregulated metabolites involved in amino acid pathways, which might indicate changes in the microbiome, were detected. In conclusion, abdominal irradiation in a nonhuman primate model caused a plasma metabolome profile indicative of GI injury. These results point to pathways that may be targeted for intervention or used as early indicators of GI radiation injury. Moreover, our results suggest that effects are sex-specific and that interventions may need to be tailored accordingly.« less
  2. ; ; ; ( , electronic materials conference)
    Cadmium telluride (CdTe) thin-film semiconductors exhibit many desirable properties for low-cost and high-efficiency photovoltaic (PV) technology, including inherent robustness of inorganic absorber, a direct bandgap that allows full absorption of the solar spectrum with thicknesses of only few microns, and inexpensive and high-throughput manufacturing processes. At the best efficiency of 22 %, the power conversion efficiency of CdTe PVs is still well below the maximum theoretical limit (approximately 30 %). It has been suggested that the inferior efficiency is mainly attributed to the inherent polycrystalline nature of CdTe absorber (e.g., grains, grain boundaries). Understanding local photocarrier dynamics is vital tomore »overcoming roadblocks toward higher efficiency CdTe PVs. However, conventional cell-level PV measurements often limit the microstructural analysis. In this work, we present a local PV characterization technique using point back-contacts. The thin-film CdTe solar cells used in this work were prepared by CSS (close-spaced sublimation) on a stack of n-type window layer (e.g., CdS) / transparent conductive layer (TCO; e.g., SnO2) / glass substrate.« less
  3. ; ; ; ; ; ; ( , Energy & Environmental Science)
    Future high performance PV devices are expected to be tandem cells consisting of a low bandgap bottom cell and a high bandgap top cell. In this study, we developed a cradle-to-end of use life cycle assessment model to evaluate the environmental impacts, primary energy demand (PED), and energy payback time (EPBT) of four integrated two-terminal tandem solar cells composed of either Si bottom and lead-based perovskite (PK Pb ) top cells (Si/PK Pb ), copper indium gallium selenide (CIGS) and PK Pb (CIGS/PK Pb ), copper zinc tin selenide (CZTS) and PK Pb (CZTS/PK Pb ), or tin-lead based perovskitemore »(PK Sn,Pb ) and PK Pb (PK Sn,Pb /PK Pb ). Environmental impacts from single junction Si solar cells were used as a reference point to interpret the results. We found that the environmental impacts for a 1 m 2 area of a cell were largely determined by the bottom cell impacts and ranged from 50% (CZTS/PK Pb ) to 120% of those of a Si cell. The ITO layer used in Si/PK Pb , CZTS/PK Pb , and PK Sn,Pb /PK Pb is the most impactful after the Si and CIGS absorbers, and contributed up to 70% (in PK Sn,Pb /PK Pb ) of the total impacts for these tandem PVs. Manufacturing a single two-terminal device was found to be a more environmentally friendly option than manufacturing two constituent single-junction cells and can reduce the environmental impacts by 30% due to the exclusion of extra glass, encapsulation, front contact and back contact layers. PED analysis indicated that PK Sn,Pb /PK Pb manufacturing has the least energy-intensive processing, and the EPBTs of Si/PK Pb , CIGS/PK Pb , CZTS/PK Pb , and PK Sn,Pb /PK Pb tandems were found to be ∼13, ∼7, ∼2, and ∼1 months, respectively. On an impacts per kW h of Si basis the environmental impacts of all the devices were much higher (up to ∼10 times). These results can be attributed to the low photoconversion efficiency (PCE) and short lifetime that were assumed. While PK Sn,Pb /PK Pb has higher impacts than Si based on current low PCE (21%) and short lifetime (5 years) assumptions, it can outperform Si if its lifetime and PCE reach 16 years and 30%, respectively. Among the configurations considered, the PK Sn,Pb /PK Pb structure has the potential to be the most environmentally friendly technology.« less
  4. ; ; ; ; ; ; ; ; ( , Science Advances)
    The direct detection of 5-MeV protons by flexible organic detectors based on thin films is here demonstrated. The organic devices act as a solid-state detector, in which the energy released by the protons within the active layer of the sensor is converted into an electrical current. These sensors can quantitatively and reliably measure the dose of protons impinging on the sensor both in real time and in integration mode. This study shows how to detect and exploit the energy absorbed both by the organic semiconducting layer and by the plastic substrate, allowing to extrapolate information on the present and pastmore »irradiation of the detector. The measured sensitivity, S = (5.15 ± 0.13) pC Gy −1 , and limit of detection, LOD = (30 ± 6) cGy s −1 , of the here proposed detectors assess their efficacy and their potential as proton dosimeters in several fields of application, such as in medical proton therapy.« less
  5. ; ; ; ; ; ; ( , Conference record of the IEEE Photovoltaic Specialists Conference)
    Cadmium telluride and silicon are among the widely used absorber materials in photovoltaic industry. A tandem solar cell of these two can absorb significant portion of solar spectrum to yield high efficiency due to the added voltage of the two solar cells. On basis of low-cost production, a CdTe/Si cell has the potential to produce low-cost and high efficiency tandem PV. The CdTe top cell in a substrate configuration is essential to achieve a tandem between CdTe and Si. A functional CdS/CdTe solar cell in the substrate configuration was fabricated on a Si wafer. Current -Voltage measurements show a diode-likemore »curve with lower J-V parameters compared to standard CdS/CdTe cells. SCAPS simulations were performed to identify possible reasons for poor performance and help improve the device performance.« less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email