3 years ago

Disentangling “Bright” and “Dark” Interactions in Ordered Assemblies of Organic Semiconductors

Disentangling “Bright” and “Dark” Interactions in Ordered Assemblies of Organic Semiconductors
Michael D. Barnes, Peijian Wang
We report on spatially correlated wavelength-resolved photoluminescence and Kelvin probe force microscopy to probe ground state charge-transfer coupling and its correlation with pi-stacking order in nanoscale assemblies of a small molecule n-type organic semiconductor, tetraazaterrylene (TAT). We find a distinct upshift in surface potential contrast (SPC) corresponding to a decrease in work function in TAT in the transition from disordered spun-cast films to ordered crystalline nanowire assemblies, accompanied by a nanowire size dependence in the SPC shift suggesting that the shift depends on both ground state charge transfer interaction and a size (volume)-dependent intrinsic doping associated with the nitrogen substitutions. For the smallest nanowires studied (surface height ≈ 10–15 nm), the SPC shift with respect to disordered films is +110 meV, in close agreement with recent theoretical calculations. These results illustrate how “dark” (ground-state) interactions in organic semiconductors can be distinguished from “bright” (excited-state) exciton coupling typically assessed by spectral measurements alone.

Publisher URL: http://dx.doi.org/10.1021/acs.nanolett.7b03394

DOI: 10.1021/acs.nanolett.7b03394

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