Optically accessible long-lived electronic biexcitons at room temperature in strongly coupled H- aggregates

• Published in: Nature communications 2024-09, Vol.15 (1), p.8280-9, Article 8280
• Main Authors: Sohoni, Siddhartha, Ghosh, Indranil, Nash, Geoffrey T., Jones, Claire A., Lloyd, Lawson T., Li, Beiye C., Ji, Karen L., Wang, Zitong, Lin, Wenbin, Engel, Gregory S.
• Format: Article
• Language: English
• Subjects: 140/125; 639/638/440/527; 639/638/440/949; 639/638/541/966; Absorption; Aggregates; Chromophores; Electrons; Energy; Energy harvesting; Excitons; Holes (electron deficiencies); Humanities and Social Sciences; Hydrogen; Light; Microscopy; multidisciplinary; Photon absorption; Photons; Photovoltaic cells; Photovoltaics; Room temperature; Science; Science (multidisciplinary); Temperature
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-52341-2

Photon absorption is the first process in light harvesting. Upon absorption, the photon redistributes electrons in the materials to create a Coulombically bound electron-hole pair called an exciton. The exciton subsequently separates into free charges to conclude light harvesting. When two excitons are in each other’s proximity, they can interact and undergo a two-particle process called exciton-exciton annihilation. In this process, one electron-hole pair spontaneously recombines: its energy is lost and cannot be harnessed for applications. In this work, we demonstrate the creation of two long-lived excitons on the same chromophore site (biexcitons) at room temperature in a strongly coupled H-aggregated zinc phthalocyanine material. We show that exciton-exciton annihilation is suppressed in these H- aggregated chromophores at fluences many orders of magnitudes higher than solar light. When we chemically connect the same aggregated chromophores to allow exciton diffusion, we observe that exciton-exciton annihilation is switched on. Our findings demonstrate a chemical strategy, to toggle on and off the exciton-exciton annihilation process that limits the dynamic range of photovoltaic devices. When excitons in light-harvesting materials meet, they recombine and dissipate their energy. Here, the authors show that pairs of excitons can co-exist in aggregated materials and only annihilate when the aggregates are chemically connected.