Energy Transfer and Exciplex Formation and Their Impact on Exciton and Charge Carrier Dynamics in Organic Films

We report Förster resonant energy transfer (FRET) with a Förster radius <i>R</i>₀ of 4.8 nm and exciplex formation in composites containing two functionalized anthradithiophene (ADT) derivatives, ADT-TES-F (donor, D) and ADT-TIPS-CN (acceptor, A) depending on the D−A distance. In composites containing bulk D/A heterojunctions, exciplex photoluminescence (PL) emission peaked at ∼668 nm dominated the PL spectra. The exciplex contributed to charge carrier photogeneration on nanosecond time scales in composites, in contrast to sub-500 ps carrier photogeneration observed in ADT-TES-F pristine films. Finally, significantly slower charge carrier recombination was obtained in composites, as compared to that of pristine ADT-TES-F films, due to electron trapping at the ADT-TIPS-CN enabling the hole to propagate in the ADT-TES-F host

Intrinsic Charge Trapping Observed as Surface Potential Variations in diF-TES-ADT Films

Spatial variations in surface potential are measured with Kelvin probe force microscopy for thin films of 2,8-difluoro-5,11-bis­(triethyl­silyl­ethynyl)­anthra­dithio­phenes (diF-TES-ADT) grown on SiO₂ and silane-treated SiO₂ substrates by organic molecular beam deposition. The variations are observed both between and within grains of the polycrystalline organic film and are quantitatively different than electrostatic variations on the substrate surfaces. The skewness of surface potential distributions is larger on SiO₂ than on HMDS-treated substrates. This observation is attributed to the impact of substrate functionalization on minimizing intrinsic crystallographic defects in the organic film that can trap charge

Understanding Heterogeneous Nucleation in Binary, Solution-Processed, Organic Semiconductor Thin Films

Heterogeneous nucleation is often the precursor to crystallization in solution-processed organic semiconductor thin films. Here, we study the efficacy of a series of nine small-molecule organic semiconductor additives in seeding the crystallization of solution-processable triethylsilylethynyl anthradithiophene (TES ADT). By systematically varying the concentrations of the additives in TES ADT thin films, we found the tendency of the additives to crystallize, their solubility in the casting solvent, and their similarity in chemical structure to TES ADT, to determine the nucleation and resulting density of nuclei. Tracking the crystallization process further yields information about the mechanism of nucleation. While pure TES ADT nucleates instantaneously at the onset of crystallization, nucleation transitions to a distributed process occurring throughout crystallization with the incorporation of increasing amounts of additives

Influence of Solid-State Microstructure on the Electronic Performance of 5,11-Bis(triethylsilylethynyl) Anthradithiophene

The rich phase behavior of 5,11-bis­(triethylsilylethynyl) anthradithiophene (TES ADT) – one of the most promising, solution-processable small-molecular organic semiconductors – is analyzed, revealing the highest performing polymorph among four solid-state phases, opening pathways toward the reliable fabrication of high-performance bottom-gate/bottom-contact transistors