Investigating the dielectric properties and exciton diffusion in C₇₀ derivatives

Abstract

In recent years, the dielectric constant (εr) of organic semiconductors (OSCs) has been of interest in the organic photovoltaic (OPV) community due its potential influence on the exciton binding energy....

The Effect of Fluorinated Benzothiadiazole-dicyanovinyl Acceptors on the Dielectric Constants of Organic Photovoltaic Materials

“…40−43 At the lowest frequency measured the ε lf was over 13, which is well above the value theoretically required to enable spontaneous exciton separation into free charge carriers, which is a requirement for single component OPV devices. In contrast, ε opt of the as-cast film of the nonfluorinated analogue (4.6 at 10 14 Hz, the regime where exciton dissociation occurs) 23,44 was higher than that of the fluorinated material (4.0). The higher ε opt of the as-cast protonated dimer is consistent with the fact that the film had an increased order with a more pronounced out-of-plane chromophore arrangement than that of D(CPDT-DFBT-DCV), which formed an amorphous as-cast film.…”

The effect of fluorination on the low and high frequency dielectric constants of non-polymeric organic semiconductors – towards homojunction solar cells

“…13,14 While the dipolar effect can be relatively large, reorientation of dipoles occurs slowly (10-10 7 Hz) 13 with respect to the lifetime of the exciton (typically pico-to nanoseconds for fluorescent materials), 15 and hence its contribution to lowering the exciton binding energy is expected to be small. 16 However, the bimolecular recombination of photogenerated charge carriers in organic semiconductors occurs over a larger time range, 100 ns-10 ms for a localised polaron, 17 and so this loss mechanism will be suppressed by an increased dielectric constant in the kHz-MHz range. 18,19 Therefore, the optical frequency dielectric constant (e opt ), determined by electronic contributions, is expected to influence the exciton binding energy and the ability to achieve direct free charge carrier generation upon photoexcitation.…”

Strategies for Enhancing the Dielectric Constant of Organic Materials

“…Finding design rules for specific applications helps navigate through this vast chemical space toward better performing devices with desired properties. The use of high dielectric constant materials is one such design rule that has attracted significant attention in the fields of organic photovoltaics (OPVs), − organic thermoelectrics (OTEs), − and organic transistors. ,− …”

“…A strategy that has been consistently successful and has become the preeminent way to obtain high static dielectric constant organic electronics is the use of ethylene glycol (EG) side chains . These side chains have been added to fullerene derivatives, − ,− , small molecules, − ,, and polymers − ,− and have in turn resulted in increased static dielectric constants. Notably, recent work from Rousseva et al reached a record static dielectric constant for fullerene derivatives (ϵ r > 10) with the BPEG-2 molecule (see Figure ).…”