Dichlorinated Dithienylethene‐Based Copolymers for Air‐Stable n‐Type Conductivity and Thermoelectricity

Abstract

Two donor–acceptor (D–A) polymers are obtained by coupling difluoro‐ and dichloro‐substituted forms of the electron‐deficient unit BDOPV and the relatively weak donor moiety dichlorodithienylethene (ClTVT). The conductivity and power factors of doped devices are different for the chlorinated and fluorinated BDOPV polymers. A high electron conductivity of 38.3 and 16.1 S cm−1 are obtained from the chlorinated and fluorinated polymers with N‐DMBI, respectively, and 12.4 and 2.4 S cm−1 are obtained from the chlorinated and fluorinated polymers with CoCp2, respectively, from drop‐cast devices. The corresponding power factors are 22.7, 7.6, 39.5, and 8.0 µW m−1 K−2, respectively. Doping of PClClTVT with N‐DMBI results in excellent air stability; the electron conductivity of devices with 50 mol% N‐DMBI as dopant remained up to 4.9 S m−1 after 222 days in the air, the longest for an n‐doped polymer stored in air, with a thermoelectric power factor of 9.3 µW m−1 K−2. However, the conductivity of PFClTVT‐based devices can hardly be measured after 103 days. These observations are consistent with morphologies determined by grazing incidence wide angle X‐ray scattering and atomic force microscopy.

A high-conductivity n-type polymeric ink for printed electronics

“…3b). This stability is induced by the combination of high work function (4.19 eV, vide infra) and selfencapsulation in the micrometer-thick film, which inhibits the penetration of H 2 O and O 2 , as also observed for other recently reported n-doped polymers 42 . The electrical conductivity of thinner films (~100 nm) drops to 0.1 S cm −1 after 10 days in air, whereas we observed a decrease of <10% over 120 days when the thin films are stored in inert atmosphere (Supplementary Fig.…”

n-Type organic semiconducting polymers: stability limitations, design considerations and applications

“…20). 67 Despite the two polymers sharing an identical backbone, the replacement of chlorine with fluorine atoms on the electron-deficient BDOPV unit has a remarkable influence on the s max , which is rationalised with the same explanation as for the BDPPV polymer series. Indeed, s max of PClClTVT is 16.1 S cm À1 , which is less than half that of PFClTVT (38.3 S cm À1 ), furthermore the PF of PFClTVT reached 22.7 mW m À1 K À2 , three times that of PFClTVT (Table 10).…”

“…Indeed, s max of PClClTVT is 16.1 S cm À1 , which is less than half that of PFClTVT (38.3 S cm À1 ), furthermore the PF of PFClTVT reached 22.7 mW m À1 K À2 , three times that of PFClTVT (Table 10). 67 Once again, the drastically improved s max and resultant TE performance of both these materials, particularly PFClTVT, are dominated by the charge carrier mobility, following eqn (5). It should also be noted that the authors reported that PClClTVT, doped with 50 mol% N-DMBI, retained a s max value of 4.9 S cm À1 after storing in air for 222 days, a very considerable stability for an n-doped polymer stored in air.…”

“…28 More generally, n-type materials tend to comprise of a selection of electron deficient units, including naphthalenediimide (NDI), 55 diketopyrrolopyrrole (DPP) 56 or isoindigo (IIG). 57 The synthetic techniques for deepening the LUMO level of an OSC include extending the conjugation length, 58,59 the introduction of heteroatoms into the polymer backbone, [60][61][62] decreasing the dilution effect to reduce the electron density in the polymer backbone, 63 increasing backbone planarization, 36,64,65 addition of electron-withdrawing groups, 62,66,67 and the use of an all acceptor motif to delocalise the LUMO (Fig. 4).…”

“…It should also be noted that the authors reported that PClClTVT, doped with 50 mol% N-DMBI, retained a s max value of 4.9 S cm À1 after storing in air for 222 days, a very considerable stability for an n-doped polymer stored in air. 67 4.3.3. Naphthodithiophenediimide-based (NDTI) copolymers.…”