Light‐harvesting properties of a subphthalocyanine solar absorber coupled to an optical cavity

Herein, both from the experimental and theoretical point of view, the optical absorption properties of a subphthalocyanine (SubPc), an organic macrocycle commonly used as a sunlight harvester, coupled to metallic optical cavities are analyzed. How different electronic transitions characteristic of this compound and specifically those that give rise to excitonic (Q band) and charge transfer (CT band) transitions couple to optical cavity modes is investigated. It is observed that whereas the CT band couples weakly to the cavity, the Q band transitions show evidence of hybridization with the photon eigenstates of the resonator, a distinctive trait of the strong coupling regime. As a result of the different coupling regimes of the two electronic transitions, very different spectral and directional light-harvesting features are observed, which for the weakly coupled CT transitions are mainly determined by the highly dispersive cavity modes and for the strongly coupled Q band by the less angle-dependent exciton-polariton bands. Modeling also allows discriminating parasitic from productive absorption in each case, enabling the estimation of the expected losses in a solar cell acting as an optical resonatorFunding for this work was provided by the Spanish “Ministerio de Ciencia, Innovación y Universidades (MCIU)” through AEI/FEDER(UE) projects MAT2017-88584-R (MODO), RTI2018-099737-B-I00, CTQ2017-85393-P and PID2020-116490GBI00, as well as through projects EXPLORA FIS2017-91018-EXP, PCI2018-093145 (QuantERA program, EC), CEX2018-000805-M (María de Maeztu Programme for Units of Excellence in R&D), SEV2016-0686 (Severo Ochoa Programme for Centres of Excellence in R&D), and MODE-Fotovoltaica (Materiales Orgánicos Disruptivos para Energía Fotovoltaica) (RED2018-102815-T). V.E. thanks La Caixa Foundation (ID 100010434) for funding of her Ph.D. (fellowship LCF/BQ/ES15/10360025). L.C. thanks Junta de Andalucia and the European Regional Development Funds program (EU-FEDER) for financial support (DOC_00220). This work was partially funded also by the European Research Council through Grant No. ERC-2016-StG-71487