Researchers Demonstrate Recovery of Spin-Triplet Excitons in Organic Photovoltaics for Improved Efficiency

Researchers have experimentally demonstrated in an organic photovoltaics system with a non-fullerene acceptor featuring a narrowed singlet-triplet gap that low-energy spin-triplet excitons, known as T1, can be redissociated through the interfacial charge-transfer state to form free carriers.

This redissociation process was corroborated by identifying an increased population of free carriers following triplet sensitization of the acceptor in an OPV blend. Non-geminate recombination in organic photovoltaics forms these T1 excitons, which typically result in irreversible, non-radiative relaxations.

The distribution of orbitals in the molecule and exciton delocalization in aggregates influence the singlet-triplet energetics of the acceptor in the condensed phase. Traffic between T1 and the spin-triplet charge-transfer state becomes controllable due to these singlet-triplet energetics in the condensed phase.

Researchers introduced the acceptor as a ternary component into other host OPV systems.

This introduction recovered triplet-mediated losses and improved OPV efficiencies by maximizing the number of extractable photocarriers. The study shows the recovery of low-energy T1 excitons into usable charges for electricity or light generation instead of heat. Nature reported these findings in the research paper titled 'Recycling of spin-triplet excitons in organic photovoltaics'.

The paper is published in Nature. Figure 1 illustrates the dynamics corresponding to redissociation of triplet excitons measured by fs-TAS. Figure 2 depicts charge recombination dynamics in blend films measured by ns-TAS.