‘Remarkable’ Binary OSC Efficiency

• PolyU has achieved a PCE of 19.31% claiming it to be the highest for binary OSCs
• The team developed a new non-monotonic ISM strategy, simultaneously optimizing crystallization dynamics
• They see this growth in efficiency for OSC to lead to tremendous opportunities for BIPV applications

The Hong Kong Polytechnic University (PolyU) has announced achieving a 'remarkable' binary organic solar cells (OSC) of 19.31% (18.93% certified), which it claims to be the highest efficiency for binary OSC's so far, one that will likely create tremendous opportunities for building integrated PV (BIPV) applications.

Chair Professor of Energy Conversion Technology and Sir Sze-Yen Chung Endowed Professor in Renewable Energy at PolyU, Prof Li Gang said, "The new door will open when low cost single-junction OSCs can achieve a PCE of over 20%, along with more stable performance and other unique advantages such as flexibility, transparency, stretchability, low weight and tuneable colour."

They managed it with the invention of a 'novel' OSC morphology-regulating technique by using 1,3,5-tricholobezene as a crystallization regulator that helped boost efficiency and stability. For their research, the team developed a non-monotonic intermediated state manipulation (ISM) strategy to manipulate the bulk-heterojunction (BHJ) OSC morphology, parallelly optimizing crystallization dynamics and energy loss of non-fullerene OSC.

It also reduced non-radiative recombination loss which is known to bring down efficiency and increase heat loss.

"Challenges in research came from the existing additive-based benchmark morphology control methods, which suffer from non-radiative recombination loss, thus lowering the open-circuit voltage due to excessive aggregation," said Gang.

Gang's team says the ISM strategy promotes the formation of more ordered molecular stacking and favorable molecular aggregation, unlike using traditional solvent additives based on excessive molecular aggregation in films. It took the team about 2 years to develop the ISM strategy.

The team's work has been published in the scientific journal Nature Communications with the title 19.3% Binary Organic Solar Cell and Low Non-Radiative Recombination Enabled by Non-Monotonic Intermediate State Transition.