Frenkel-Holstein Hamiltonian Applied to Quaterthiophene-based 2D Hybrid Organic-Inorganic Perovskites

In two-dimensional hybrid organic-inorganic perovskites (HOIPs), both the organic and inorganic components can contribute to the electronic properties at the electronic frontier levels and hence open up a wide area for design of new materials with high tunability. For development of new devices like solar cells or light emitting diodes, the understanding of electronic excitations and their photophysical signatures plays a fundamental role. Here, we show by the example of quaterthiophene-based lead-halide HOIPs that the organic contribution to 2D HOIP absorption spectra can be theoretically appreciated employing a Frenkel-Holstein Hamiltonian that treats electronic coupling and electron-phonon coupling on equal footing. We relate changes in the spectra to structural changes in the organic layer that in turn are caused by variation of the halide anion. Specifically, we find that the strength of the excitonic coupling on the organic component decreases when the halide anion is varied from Cl to Br to I. Our research opens up a potential pathway for predicting optoeletronic properties of newly designed 2D HOIPs.