Impact of Photoluminescence Imaging Methodology on Transport Parameters in Semiconductors

Abstract

Triplet−triplet annihilation-induced delayed emission provides a pathway for investigating triplets via emission spectroscopy. This bimolecular annihilation depends directly on the transport properties of triplet excitons in disordered organic semiconductors. Photoluminescence (PL) imaging is a direct method for studying exciton and charge-carrier diffusivity. However, most of these studies neglect dispersive transport. Early time scale measurements using this technique can lead to an overestimation of the diffusion coefficient (D T ) or diffusion length (L d ). In this study, we investigated the time-dependent triplet D T using PL imaging. We observed an overestimation of L d in classical delayed PL imaging, often 1 order of magnitude higher than the actual L d value. We compared various thicknesses of polymeric thin films to study the dispersive nature of triplet excitons. Transient analysis of delayed PL imaging and steady state imaging reveals the importance of considering the time-dependent nature of D T for the triplet excitons in disordered electronic materials.

Transport, trapping, triplet fusion: thermally retarded exciton migration in tetracene single crystals

“…At early times after photoexcitation, this population has several possibilities to energetically relax into lower lying states via the emission of phonons, resulting in high mobility, which, however, decreases as soon as the population has relaxed into sites from where transport can only occur through thermally activated hopping. The impact of an apparent time-dependent diffusivity on lateral transport measurements was recently also discussed for other disordered systems, 42,56 and yields surprisingly high effective diffusion coefficients at early times (first few ns) after excitation through a laser pulse.…”