Researchers from The Hong Kong Polytechnic University (PolyU) have achieved a breakthrough power-conversion efficiency (PCE) of 19.31% with organic solar cells (OSCs) which will help enhance applications of these advanced solar energy devices
The PCE is considered a benchmark for the performance of photovoltaics (PVs) in power generation. The improved efficiency of more than 19% that has now been achieved constitutes a record for binary OSCs which have one donor and one acceptor in the photo-active layer.
The research team, which was led by PolyU’s Li Gang, professor of energy conversion technology, and Sir Sze-Yen Chung, endowed professor in renewable energy, invented a novel OSC morphology-regulating technique by using 1,3,5-trichlorobenzene as a crystallisation regulator. This new technique boosts OSC efficiency and stability.
The team developed a non-monotonic intermediated state manipulation (ISM) strategy to manipulate the bulk-heterojunction (BHJ) OSC morphology and simultaneously optimise the crystallisation dynamics and energy loss of non-fullerene OSCs. Unlike the strategy of using traditional solvent additives, the ISM strategy promotes the formation of more ordered molecular stacking and favourable molecular aggregation. As a result, the PCE was considerably increased and the undesirable non-radiative recombination loss was reduced. Non-radiative recombination lowers the light generation efficiency and increases the heat loss.
Gang commented, “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.” The research team took about two years to devise a non-monotonic ISM strategy for increasing the OSC efficiency and lowering the non-radiative recombination loss. The publication of the study – in Nature Communications – promises to galvanise OSC research.
“The new finding will make OSC research an exciting field, and this will likely create tremendous opportunities in applications like portable electronics and building-integrated PVs,” Gang continued.