Tertiary Carbonate Side Chains: Easily Tunable Thermo-labile Breaking Points for Controlling the Solubility of Conjugated Polymers

Abstract

Breakpoints are not exclusive to tennis: We present a new class of solubilizing groups for conjugated polymers which enable solution processing of multi-layer devices. Conjugated polymers in organic devices are sometimes difficult to process due to their limited solubility. Well soluble polymers decorated with alkyl side chains, however, introduce new challenges for thin-film deposition: Using the same solvent for multiple layers can dissolve the already applied layers. In this work we introduce a new class of thermo-labile groups which reduce the solubility of conjugated polymers after thermal treatment. Following a very modular approach, we can tune the temperature of the thermo-cleavage between 140 and 200 °C.

Morphological, Chemical, and Electronic Changes of the Conjugated Polymer PTB7 with Thermal Annealing

“…The double transition in TGA is consistent with the previous literature on side-chain-cleavable materials, in which the first TGA mass loss is attributed to side chain cleavage ( Guo et al., 2015 , Helgesen et al., 2011 , Vahdani et al., 2016 , Kuhn et al., 2015 ). Furthermore, the solubility of PTB7 powder dropped significantly after annealing at 290°C, with visible precipitates remaining in a 10-mg/mL solution in chlorobenzene after stirring for several hours at 60°C.…”

“…Thermo-cleavable side chains have been shown to have several advantages: increase in backbone planarity ( Guo et al., 2015 ), increase in efficiency in some devices, improvement in device stability ( Manceau et al., 2010 , Helgesen et al., 2011 ), suppression of PCBM aggregation in blends ( Vahdani et al., 2016 ), and decrease in solubility of the film, allowing multilayer processing ( Kuhn et al., 2015 ). In many cases, cleavage occurs at the ester group, leaving a carboxyl group ( Manceau et al., 2010 , Helgesen et al., 2011 ) or removing the ester group entirely ( Guo et al., 2015 , Kuhn et al., 2015 , Höfle et al., 2017 , Hillebrandt et al., 2016 ). In polymers based on the poly(thieno[3,4-b]thiophene-benzo[1,2-b:4,5-b′]dithiophene) (PTB) backbone, cleavage occurs at the ether group, yielding a hydroxyl group ( Vahdani et al., 2016 ).…”

Design directed self-assembly of donor–acceptor polymers

“…The main requirement is that the electronic nature of the polymer backbone remains unperturbed by the bond scission. The cleavage mechanism of the substituents has been well described for polythiophenes as model systems 71 and the approach has been recently transferred to a series of narrow band gap D-A polymers comprising tert-butoxycarbonyl (t-Boc) substituted indigo (22a), isoindigo (22b) or diketopyrrolopyrrole (22c) as the acceptor and benzodithiophene as donor moiety (Fig. 15).…”

Naphthalene Tetracarboxydiimide-Based n-Type Polymers with Removable Solubility via Thermally Cleavable Side Chains

“…Both side groups are expected to undergo thermal decomposition liberating gaseous CO 2 as well as a volatile alkene to give a primary alcohol or the free imide, respectively. We recently presented the feasibility of this approach and the control of the scission temperature for polythiophenes …”

“…We recently presented the feasibility of this approach and the control of the scission temperature for polythiophenes. 22 Especially, the possible intermolecular H-bonding motif of the free imide is expected to dramatically reduce the solubility of the resulting compounds. We study the mechanism of the pyrolysis process in the polymer films in detail via X-ray photoelectron spectroscopy (XPS) and infrared transmission spectroscopy (IRS), giving insight into chemical composition.…”