Extended Data Fig. 5: Fourier transform photocurrent spectrum of the BTA3-based OLEDs.
From: Ultrahigh-radiance near-infrared organic light-emitting diodes
EU of 26.9 meV was extracted according to Urbach’s rule α(E)=α_0 e^((E-E_g)/E_U), where α(E) is the optical absorption coefficient or EQE, EU is the Urbach energy, Eg is the optical bandgap. The low energetic disorder is important for an increased exciton diffusion length, as it corresponds to a high density of available sites within the energy transfer radius and enables more efficient exciton diffusion40. The exciton diffusion coefficient (D) be estimated from the TTA rate coefficient through a time-independent formula (see Supplementary Note 4). With the k_TT extracted from Extended Data Fig. 3 and Extended Data Fig. 4, a triplet exciton diffusion coefficient of 1.6×10−4 cm2 s−1 and a long exciton diffusion length (LD) of 50 nm were obtained. The LD of BTA3 is much longer than the typical singlet of 5–10 nm and comparable to the values typically obtained for organic single crystals50. The enhanced triplet exciton diffusion can be ascribed to strong intermolecular interactions and enhanced electron delocalization of the A–D–A molecule, which enable short-range Dexter energy transfer43.
