Researchers in Japan have developed an effective PET faceplate encapsulation for copper-indium-gallium-diselenide mini-modules. The laboratory devices passed the moist heat tests and retained approximately 97% of initial efficiency after 3,600 hours.
Researchers from Ritsumeikan University in Japan have tested a new type of polyethylene terephthalate (PET) cover sheet and related encapsulation methods to improve the durability of copper-indium gallium diselenide (CIGSe) mini solar modules. They found that such devices exposed to moist heat tests for 3,600 hours retained about 97% of their initial efficiency.
The research is part of an ongoing effort towards robust and lightweight glass-free thin-film PV modules for a range of applications. “This work addresses the encapsulation of the CIGSe device with a film shell with high barrier layers for future lightweight and flexible devices,” the study’s corresponding author Minemoto Takashi shared. pv magazine.
The researchers chose to study polyethylene terephthalate (PET) film because it is preferred for flexible solar panels for reasons such as chemical resistance, but research on such materials is limited.
In the study, researchers used a flexible, high-barrier PET precoat with a WVTR of 10-3 g/m2/day and a black polymer tape sealant to further improve encapsulation. Additionally, they applied a passivating bias, which played a “critical role” in stabilizing the performance of the CIGSe mini-modules during the moist heat test.
In the experiments two 6 cm2 CIGSe mini-modules with initial efficiencies of 18.33% and 18.34% were provided by the National Institute of Advanced Industrial Science and Technology (AIST). One was continuously biased near the voltage at maximum power point (Vmpp) and the other remained under unbiased conditions.
The encapsulation structure was as follows: a flexible PET front sheet/a thermoplastic polyolefin (TPO) encapsulant/CIGSe mini module/TPO, PET-Al back sheet. Both the front cover and back cover were supplied by Japan-based Dai Nippon Printing.
“This combination of materials provides flexibility and minimizes damage during the lamination process, which involves a vacuum lamination and pressing process at 150 C for 6 minutes at 100 kPa,” the researchers said.
The moist heat (DH) tests showed that “both biased and unbiased mini modules exhibited good stability during the first 1,872 hours of the DH test, maintaining high performance with efficiency retention of 100% and 97%, respectively,” the researchers said, noting that the biased PET/TPO combination performed even better and showed “remarkable stability” after more than 3,000 hours, retaining approximately 97% of their initial efficiency.
“This high stability indicates the effectiveness of the encapsulation structure, especially the suitability of the top cover sheet during the DH test. Therefore, the proposed encapsulation structure is potentially more stable when coupled with a cover sheet with a higher WVTR,” the researchers said.
“The high-barrier flexible faceplate enables glass-free encapsulation and flexible modules, overcoming the limitations of traditional glass encapsulation,” the team concluded. They also emphasized that “maintaining a stable and well-regulated preload” could further improve long-term durability and provide better performance retention.
Further research into scaling up the use of the materials evaluated in the study was recommended, as well as field testing and a systematic investigation into the effects of electrical bias.
The work is described in detail in “Cu(In,Ga)Se2 mini-modules demonstrate moist heat stability of over 3000 hours via advanced encapsulation and bias management”, published in Solar energy. The research participants were from Dai Nippon Printing Co. and the National Institute of Advanced Industrial Science and Technology (AIST).
Looking ahead, the research group is working on technology needed to build integrated PV applications (BIPV). “Our next goal is a perovskite-CIGS tandem device with light weight and flexibility for extensive PV applications such as lightweight roofs, building facades and mobility,” said Takashi.
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