Large‐Scale Determination of Frontier Orbital Energies of Disordered Small‐Molecule Organic Semiconductors Using Exciplex Emission Spectra

Abstract

ABSTRACT Accurately knowing the frontier orbital energies of the structurally disordered small‐molecule organic semiconductors that are used in optoelectronic devices such as organic light‐emitting diodes is required to rationally improve their performance. Here, we show that these energies can be deduced with a large accuracy from the peak energies of photoluminescence spectra of donor:acceptor blends with a 1:1 composition ratio, showing emission from intermolecular charge‐transfer states (exciplexes). This “exciplex data base method” (EDBM) is applied to more than 160 donors and 180 acceptors, using more than 550 spectra. The key finding is that the effective exciplex binding energy shows a surprisingly small variation within the available database. Its average value of 1.0 eV is argued to be larger than the adiabatic value due to spectral redshifts as a result of exciplex diffusion, exciplex‐vibron coupling and a Stokes shift. The database is highly redundant, and allows obtaining relative accuracies better than 0.1 eV. Calibration using the frontier orbital energies of well‐studied materials leads to precise absolute values, as deduced from a comparison with spectroscopic data. The method is easy and fast, can be readily applied to novel materials, and provides thereby an accurate basis for predictive device simulations.