Light-Harvesting Properties of a Subphthalocyanine Solar Absorber Coupled to an Optical Cavity

Abstract

Herein, both from the experimental and theoretical point of view, the opticalabsorption properties of a subphthalocyanine (SubPc), an organic macrocyclecommonly used as a sunlight harvester, coupled to metallic optical cavities areanalyzed. How different electronic transitions characteristic of this compoundand specifically those that give rise to excitonic (Q band) and charge transfer (CTband) transitions couple to optical cavity modes is investigated. It is observedthat whereas the CT band couples weakly to the cavity, the Q band transitionsshow evidence of hybridization with the photon eigenstates of the resonator, adistinctive trait of the strong coupling regime. As a result of the different couplingregimes of the two electronic transitions, very different spectral and directionallight-harvesting features are observed, which for the weakly coupled CT tran-sitions are mainly determined by the highly dispersive cavity modes and for thestrongly coupled Q band by the less angle-dependent exciton-polariton bands.Modeling also allows discriminating parasitic from productive absorption in eachcase, enabling the estimation of the expected losses in a solar cell acting as anoptical resonator.