A South Korean research team led by Korea Electronic Technology Institute (KETI) reported that quartz glass with a thermally annealed aluminum-doped zinc oxide film can provide electron radiation shielding for III-V space photovoltaic modules.
“Our work demonstrates that aluminum-doped zinc oxide (AZO)-coated quartz glass can serve as an effective radiation-shielding cover glass for space photovoltaic modules. By tailoring the AZO film properties through post-treatments, we significantly enhanced both the crystallinity and electron-radiation shielding performance, enabling improved durability of space PV modules,” Yonghwan Lee, corresponding author of the research, told pv magazine.
The researchers chose a transparent conducting oxide (TCO) coating for the cover glass as an alternative to conventional cerium-doped space cover glass. They then selected AZO as a representative TCO coating. “In addition to shielding, the TCO coating mitigates the accumulation of space charges that generate local electric fields, thereby reducing the likelihood of electrostatic discharges (ESDs) through efficient charge dissipation,” noted the researchers.
In the study, two AZO film post-treatment methods – ultraviolet (UV) treatment and thermal annealing – were tested. The team compared the performance of four substrate samples: bare quartz, the as-grown AZO, the UV-treated AZO, and annealed AZO-coated quartz.
An extensive set of tests revealed that between the two, the thermal annealing was found to be more effective at removing “residual organic compounds and solvent” and better at “inducing crystallization of the initially amorphous AZO” thin film.
It was further observed that thermal annealing enhanced its effective shielding against electron radiation. “Under electron irradiation at 1.2 MeV with a fluence of 1 × 1015 to 3 × 1015 e− cm2, the thermally annealed AZO-coated glass demonstrated superior radiation-shielding performance compared to bare quartz glass,” the researchers noted.
Subsequently, the AZO-coated glass was tested in 30 cm2 large-area modules based on 4G32C III-V photovoltaic cell technology. After electron beam irradiation, tests showed it had “only a 2.37% degradation in power conversion efficiency, whereas the module encapsulated with bare quartz glass showed a 4.18% reduction,” according to the paper.
The researchers concluded that the findings demonstrate that AZO thin films, when prepared with appropriate post-treatment, “can serve as reliable radiation-shielding layers, offering significant potential enhancement to the long-term durability and operating stability of space photovoltaic modules.”
Commenting on the manufacturability of the technology, Lee said, “The AZO films in this study were deposited using a spray-coating method, which is inherently compatible with large-area processing. We have already demonstrated uniform coatings on substrates larger than 30 cm X 30 cm, which is sufficient for module-level prototypes and can be extended to mass production,” said Lee.
The research group, which has ongoing research into cover glass materials and space modules, including radiation-resistant coatings and lightweight encapsulation, is now working on next-generation space PV modules. The aim is to make the module technology lighter in weight to help lower launch costs, and to reduce volume by being flexible and deployable, according to Lee.
The details of the study appear in “Radiation-shielding glass with tailored Al-doped zinc oxide (AZO) coatings for durable space photovoltaic modules,” published by RSC Advances. Researchers from the Korea Advanced Nanofab Center (KANC) also contributed to the work.
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