Strategy for Enhancing the Dielectric Constant of Organic Semiconductors Without Sacrificing Charge Carrier Mobility and Solubility

Abstract

Current organic semiconductors for organic photovoltaics (OPV) have relative dielectric constants (relative permittivities, ε r) in the range of 2–4. As a consequence, Coulombically bound electron‐hole pairs (excitons) are produced upon absorption of light, giving rise to limited power conversion efficiencies. We introduce a strategy to enhance ε r of well‐known donors and acceptors without breaking conjugation, degrading charge carrier mobility or altering the transport gap. The ability of ethylene glycol (EG) repeating units to rapidly reorient their dipoles with the charge redistributions in the environment was proven via density functional theory (DFT) calculations. Fullerene derivatives functionalized with triethylene glycol side chains were studied for the enhancement of ε r together with poly(p‐phenylene vinylene) and diketopyrrolopyrrole based polymers functionalized with similar side chains. The polymers showed a doubling of ε r with respect to their reference polymers in identical backbone. Fullerene derivatives presented enhancements up to 6 compared with phenyl‐C61‐butyric acid methyl ester (PCBM) as the reference. Importantly, the applied modifications did not affect the mobility of electrons and holes and provided excellent solubility in common organic solvents.

Molecular-Scale Understanding of Cohesion and Fracture in P3HT:Fullerene Blends

“…The increase in the uni-axial modulus is, however, non-linear. It is interesting that for the three simulated weight fractions (25,50, and 75%), minor differences in modulus are observed when comparing the different fullerene derivatives. As discussed earlier, for low M w P3HT, P3HT:PCBM has a marginally larger cohesion energy and also a larger uniaxial elongation modulus when compared to P3HT:ICMA, a result that may be attributed to the smaller cohesion energy for ICMA.…”

“…Electron-acceptor materials derived from fullerenes -and in particular the phenyl butyric acid methyl ester substituted C 60 and C 70 derivatives (PC 61 BM and PC 71 BM, respectively), among a multitude of others [23][24][25][26] continue to dominate the BHJ OPV literature. However, it is not clear 4 how the chemical substitution patterns of the solubilizing groups influence the electronic and mechanical properties of these composite materials, as there remain many intricate details that need to be unfurled at the molecular-and nano-scales.…”

The synthesis and purification of amphiphilic conjugated donor–acceptor block copolymers

“…27 Tetraethylene glycol was chosen for its ability not only to confer hydrophilicity, but also its demonstrated capacity to increase the dielectric constant of organic materials, thereby enhancing exciton dissociation. 28 This rational design is expected to produce materials with enhanced solubility, microphase separation, morphological reproducibility and photovoltaic performance over existing organic photovoltaic active layers.…”

Promising Strategy To Improve Charge Separation in Organic Photovoltaics: Installing Permanent Dipoles in PCBM Analogues

“…30 Studies of the performance of OPV devices containing donor and acceptor molecules functionalised with TEG side-chains [29][30] are currently in progress. Donaghey et al 31 report some encouraging outcomes of initial OPV device testing.…”