Mixed side-chain geometries for aggregation control of poly(fluorene-alt-bithiophene) and their effects on photophysics and charge transport

Abstract

In organic optoelectronics, order of conjugated molecules is required for good charge transport, but strong aggregation behavior may generate grain boundaries and trapping, opposing those benefits. Side chains on a polymer's backbone are major reason for and also tool to modify its morphological characteristics. In this report, we show on the example poly(9,9-dioctylfluorenylco-bithiophene) (F8T2) that by a combination of two types of side-chains on the backbone of equal number of carbons, one promoting crystallization, another hindering it, organization of the main chains can be controlled, without changing its major properties. We compare the traditional F8T2 derivative with octyl substituent with two modified species, one containing solely 2ethylhexyl side-chains and another with both types randomly distributed. Thermal characteristics, photophysics and morphology are compared and effects on film formation and 2 charge transport in bulk-heterojunction blends demonstrated on photovoltaic devices utilizing F8T2s as donor and the fullerene derivative ICBA as acceptor material.

The effects of a single atom substitution and temperature on electronic and photophysical properties F8T2 organic material

“…6 (a, b). The F8T2 exhibits the maximum peaks 2.84 eV (436 nm) for undoped F8T2 corresponds to the ultraviolet (UV) region, which is very well matched with experimental data 2.66 eV (465 nm) (Kettner, et al 2016). The absorbance spectrum of F8T2 decreases concomitantly with an increase in temperature where the maximum spectra of F8T2 (361 nm; 3.43 eV) are smallest at 600K.…”

“…The bandgap of pure F8T2 are in the following decreasing order: F8T2> I-doped F8T2> F-doped F8T2> Br-doped F8T2 (see Table 1). The experimental energy gap value of F8T2 is 2.49 eV wide (Kettner, et al 2016), i.e., about 0.17 eV greater than that of DFTB calculations which are very compatible with experimental data. The HOMO value for Br-doped F8T2 organic semiconductor is -3.78 eV wide, i.e., about 1.26 eV smaller than that of undoped F8T2 (-5.04 eV).…”

“…The HOMO value for F8T2 organic semiconductor is -5.04 eV wide, i.e., about 0.40 eV smaller than the experimental data (-5.44) (Kettner, et al 2016), which is more reactive, while being less stable than F8T2 at high temperatures (see Fig. 3).…”

Synthesis of Conjugated Polymers by Sustainable Suzuki Polycondensation in Water and under Aerobic Conditions

“…It should be noted that the use of surfactants is well-known in polymer chemistry but so far is limited to polymerization under miniemulsion conditions, where the organic solvent is present in more or less the usual amount. Under such conditions, the focus is the preparation of conjugated organic nanoparticles having specific dimensions and aspect ratio rather than sustainability. − Indeed, a detailed comparison of the experimental conditions of standard versus miniemulsion polymerization (see Tables S4, S6, S7, and S9 of the SI) does not show an obvious reduction of the characteristic E-factors. Moreover, an inert atmosphere was used throughout.…”

Solubilizing Side Chain Engineering: Efficient Strategy to Improve the Photovoltaic Performance of Novel Benzodithiophene‐Based (X‐DADAD)n Conjugated Polymers

“…At the same time, energy bandgaps are virtually the same for three polymers due to their effective self-organization in solid state promoting intermolecular electronic interactions. [28][29][30][31] Thioalkyl side chains downshift the HOMO and LUMO energy levels due to electron withdrawing effect of divalent sulfur from the p-orbital of the CC double bond to the vacant 3d-orbital of S atom. [32][33][34][35] Thus, higher open-circuit voltage values can be potentially achieved in solar cells based on polymers P2 and P3.…”