A group of researchers led by the Riken Center for Emergent Matter Science in Japan has fabricated an intrinsically stretchable organic photovoltaic (IS-OPV) cell that can reportedly maintain high efficiency levels while also enduring high strains and cyclic stretching durability.
In the paper “Intrinsically stretchable organic photovoltaics by redistributing strain to PEDOT:PSS with enhanced stretchability and interfacial adhesion,” published in nature communications, the scientists explained that the cell was built without an electron transport layer (ETL) and with a hole transport layer based on PEDOT:PSS incorporating the zwitterion 4-(3-ethyl-1-imidazolio)–1-butanesulfonate (ION E) additive, with the latter helping the cell achieve high stretchability by delocalizing and redistributing the strain in the absorber to the underlying layers.
“ION E substantially enhanced the stretchability of PEDOT:PSS by tuning its crystalline structure and strengthening the interfacial adhesion between the PEDOT:PSS layer and polyurethane (PU) substrate through reinforced hydrogen bonding,” they said. “Additionally, we employed a simple-terpolymerisation-based strategy to synthesize a polymer donor, namely Ter-D18, which was then mixed with the small-molecule acceptor Y6, yielding a new active system that helped achieve a high efficiency as well as superior mechanical properties.”
They also deposited eutectic gallium–indium (EGaIn) liquid metal onto the absorber as the top cathode, which they said prevented the absorber-cathode interface from affecting the device performance.
Image: Riken Center for Emergent Matter Science, nature communications, Common License CC BY 4.0
According to the research team, the proposed redistribution strategy can suppress crack initiation and propagation in the cell, which in turn reduces performance degradation under high tensile strains and repetitive strain cycles.
Tested under standard illumination conditions, the cell achieved a power conversion efficiency of 14.2%. Furthermore, it showed that, at 52% tensile strain, it still achieved an 80% efficiency. Additionally, after 100 stretching cycles at 10% strain, efficiency was still 95%.
“This device design strategy is not singularly contingent on exploiting the mechanical properties of the active layer to confer stretchability to the entire device, and holds vast potential for probing various other benchmark active systems, thereby charting a new path toward high-performance IS-OPVs fabrication,” the academics said.
Other researchers at the Riken Center for Emergent Matter Science in Japan recently fabricated a waterproof and flexible OPV solar cell that can be used in wearable electronics. At 3 micrometers thick, it is thought to be the first cell of its kind to survive a washing machine cycle and retain efficiency after multiple cycles.
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