Chinese researchers have demonstrated organic solar cells with novel encapsulation and a protective boundary layer for improved stability and efficiency. The best-performing cell based on the new approach retained 94% of its initial energy conversion efficiency after standards-based moist heat testing for 1,032 hours of moist heat and over 200 thermal cycles.
A research team in China has demonstrated organic solar cells (OSC) with a protective boundary layer and novel encapsulation that achieved high efficiency and improved stability.
The best performing cell based on the new approach retained 94% of the initial energy conversion efficiency of 18% after standards-based testing at 85 C for 1032 hours and 85% relative humidity, moist heat, and for 200 thermal cycles.
“We confirmed that OSC can be intrinsically and extrinsically stable under moist heat and thermal cycling tests,” said Chang-Qi Ma, the corresponding author of the study. pv magazine.
“In detail, we have developed a feasible method for screening the thermal stability of polymer blend films by measuring the UV-visible absorption of the blend film under thermal annealing. Second, we have solved the thermally induced interfacial degradation model and through the edge. Third, we have quantitatively analyzed the water vapor transmission through a 2D model and through the edge seals,” Ma explained.
The work began with temperature-dependent UV-visible absorption spectroscopy measurements, which allowed the research team to identify the onset temperature as the “critical threshold” for activation of the molecular mobility of polymer blends. The initial temperature was then used to screen semiconducting polymer blend candidates for thermally stable organic PV (OPV) devices.
“In addition, by investigating the interfacial degradation of thermally induced organic active layer/molybdenum trioxide (MoO3) in inverted OPVs, we have shown that introducing a thin buckminsterfullerene (C60) interlayer between the active layer and MoO3 mitigates the ‘burn-in’ degradation, ensuring high intrinsic thermal stability,” the researchers said.
Furthermore, to understand moisture diffusion across the encapsulated cells, the team developed two-dimensional (2D) planar and edge moisture diffusion kinetic models to analyze lateral water vapor diffusion, which provided the design principles of the encapsulation.
As a result, they added a hot press encapsulation step based on aluminum foil butyl tape (ABT) with a thickness of 200 μm. It enabled a “low lateral water vapor diffusion rate, effectively preventing moisture ingress,” the study said.
Testing compared the performance of a number of prototype blends made with a protective buckminsterfullerene (C60) low. These had a variety of acceptors, such as L8-BO, BTP-eC9, Y6 and BO-4Cl. The inverted cell stack was optimized as follows: indium tin oxide (ITO) substrate, zinc oxide, active layer, C60MoO3 hole transport layer and silver (Ag) contacts.
The strategy delivered “excellent stability results” under moist heat and thermal cycling testing, following the International Summit on Organic Solar Cells Stability (ISOS) dark storage (ISOS-D-3) and thermal cycling (ISOS-T-3) protocols.
The best performing device in terms of efficiency was the combination PM6:BO-4Cl:PC61PeA. It had a certified PCE of 18.0%, which the researchers say is among the highest reported efficiency for this type of device.
The devices retained 94% of their initial efficiency after 1,032 hours at 85 C with 85% relative humidity, moist heat and 200 thermal cycles (-40 C to 85 C), making the results among the highest reported for cells characterized under the aforementioned ISOS protocols, according to the article.
Future work will extend the stability-enhancing approach to large-area modules and develop printable barrier-based thin-film encapsulation to reduce costs. The group also continues to investigate the degradation behavior of OSC with long-term use.
The researchers described in detail the multiple research steps and results in “Improved moist heat and thermal cycle stability of organic solar cells”, published in nature energy. They were from Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), University of Science and Technology of China (USTC), Henan University, Hyper PV Technology and Anhui Yangde Temperature Control Technology.
This content is copyrighted and may not be reused. If you would like to collaborate with us and reuse some of our content, please contact: editors@pv-magazine.com.
