Stable High‐Conductivity Ethylenedioxythiophene Polymers via Borane‐Adduct Doping

Abstract

Efficient doping of polymer semiconductors is required for high conductivity and efficient thermoelectric performance. Lewis acids, e.g., B(C6F5)3, have been widely employed as dopants, but the mechanism is not fully understood. 1:1 “Wheland type” or zwitterionic complexes of B(C6F5)3 are created with small conjugated molecules 3,6‐bis(5‐(7‐(5‐methylthiophen‐2‐yl)‐2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl)thiophen‐2‐yl)‐2,5‐dioctyl‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione [oligo_DPP(EDOT)2] and 3,6‐bis(5''‐methyl‐[2,2':5',2''‐terthiophen]‐5‐yl)‐2,5‐dioctyl‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione [oligo_DPP(Th)2]. Using a wide variety of experimental and computational approaches, the doping ability of these Wheland Complexes with B(C6F5)3 are characterized for five novel diketopyrrolopyrrole‐ethylenedioxythiophene (DPP‐EDOT)‐based conjugated polymers. The electrical properties are a strong function of the specific conjugated molecule constituting the adduct, rather than acidic protons generated via hydrolysis of B(C6F5)3, serving as the oxidant. It is highly probable that certain repeat units/segments form adduct structures in p‐type conjugated polymers which act as intermediates for conjugated polymer doping. Electronic and optical properties are consistent with the increase in hole‐donating ability of polymers with their cumulative donor strengths. The doped film of polymer (DPP(EDOT)2‐(EDOT)2) exhibits exceptionally good thermal and air‐storage stability. The highest conductivities, ≈300 and ≈200 S cm−1, are achieved for DPP(EDOT)2‐(EDOT)2 doped with B(C6F5)3 and its Wheland complexes.

Solution‐Doped Donor–Acceptor Copolymers Based on Diketopyrrolopyrrole and 3, 3′‐Bis (2‐(2‐(2‐Methoxyethoxy) Ethoxy) ethoxy)‐2, 2′‐Bithiophene Exhibiting Outstanding Thermoelectric Power Factors with p‐Dopants

“…The optical gaps, from thin film absorption onsets, are ≈0.90 eV. Compared to polymers with thiophene‐based donors in DPP‐based polymers, [ 58–60 ] the incorporation of an O atom in direct conjugation with the thiophene units causes an increase in the internal donor strength. This imparts a stronger intermolecular charge transfer (ICT) character to the polymer backbone resulting in low optical gaps.…”

“…Due to the strong absorption overlap of polarons and charged F 4 TCNQ, [ 31 ] it is difficult to evaluate and quantify the degree of charge transfer from steady‐state UV–vis spectroscopy, unlike in our previous work. [ 58 ]…”

“…Due to the strong absorption overlap of polarons and charged F 4 TCNQ, [31] it is difficult to evaluate and quantify the degree of charge transfer from steady-state UV-vis spectroscopy, unlike in our previous work. [58] Therefore, we employed solid-state Fourier transform infrared (FTIR) spectroscopy to evaluate the degree of charge transfer (Figures S12-S14, Supporting Information). Not only is the C≡N stretch frequency highly sensitive to changes in the local Coulombic environment of the polymer, but the frequency is near 2200 cm −1 , an IR spectral window where other vibrational modes are largely absent.…”

Development of Alkylthiazole-Based Novel Thermoelectric Conjugated Polymers for Facile Organic Doping

“…Density functional theory (DFT) calculation was performed using the B3LYP method with a 6-31G basis set. The input command was # opt b3lyp/6-31g (d,p) geom = connectivity, charge = 0, and multiplicity = 1 [ 50 , 51 ].…”

In Situ Generation of n‐Type Dopants by Thermal Decarboxylation

“…[ 11–13 ] The use of p‐dopants has been particularly well studied, with several efficient and readily available p‐dopants reported since the mid‐00s, which may be added to the OSC layer via thermal deposition, through admixing, or via post‐deposition techniques. [ 14–18 ] Although n‐dopants have also been investigated for many years, their transition from fundamental research to common practice has progressed more slowly than that for p‐dopants. [ 5,11 ] One of the main obstacles has been the air sensitivity of n‐type dopants, a consequence of their typically electron rich nature.…”