Thieno[3,4-c]pyrrole-4,6-dione-Based Polymer Semiconductors: Toward High-Performance, Air-Stable Organic Thin-Film Transistors

Abstract

We report a new p-type semiconducting polymer family based on the thieno[3,4-c]pyrrole-4,6-dione (TPD) building block, which exhibits good processability as well as good mobility and lifetime stability in thin-film transistors (TFTs). TPD homopolymer P1 was synthesized via Yamamoto coupling, whereas copolymers P2-P8 were synthesized via Stille coupling. All of these polymers were characterized by chemical analysis as well as thermal analysis, optical spectroscopy, and cyclic voltammetry. P2-P7 have lower-lying HOMOs than does P3HT by 0.24-0.57 eV, depending on the donor counits, and exhibit large oscillator strengths in the visible region with similar optical band gaps throughout the series (∼1.80 eV). The electron-rich character of the dialkoxybithiophene counits in P8 greatly compresses the band gap, resulting in the lowest E(g)(opt) in the series (1.66 eV), but also raising the HOMO energy to -5.11 eV. Organic thin-film transistor (OTFT) electrical characterization indicates that device performance is very sensitive to the oligothiophene conjugation length, but also to the solubilizing side chain substituents (length, positional pattern). The corresponding thin-film microstructures and morphologies were investigated by XRD and AFM to correlate with the OTFT performance. By strategically varying the oligothiophene donor conjugation length and optimizing the solubilizing side chains, a maximum OTFT hole mobility of ∼0.6 cm(2) V(-1) s(-1) is achieved for P4-based devices. OTFT environmental (storage) and operational (bias) stability in ambient was investigated, and enhanced performance is observed due to the low-lying HOMOs. These results indicate that the TPD is an excellent building block for constructing high-performance polymers for p-type transistor applications due to the excellent processability, substantial hole mobility, and good device stability.

Double acceptor donor–acceptor alternating conjugated polymers containing cyclopentadithiophene, benzothiadiazole and thienopyrroledione: toward subtractive color organic photovoltaics

“…In addition, CPDT-TPD-CPDT-based polymers prepared by direct arylation showed lower M n values than their CPDT-BT-CPDT counterparts. It has been reported that monomers comprising carbonyl group are effective coupling partners in Stille coupling 36,37,[40][41][42][43] but less effective in direct arylation because of the presence of a base in the reaction mixture, which would affect the carbonyl groups on TPD. 62,65 Despite the use of the less reactive TPD, the successful direct arylation employing CPDT-capped TPD (M2) provides an alternative route for synthesizing new materials under simpler and more mild reaction conditions than those described above.…”

“…This is probably the result of the higher charge transport ability obtained by the insertion of the bithiophene unit. 23,37,[68][69][70] Other polymers showed rather poor PCEs, possibly due to low J sc values resulting from inefficient charge transport.…”

“…[36][37][38][39] An impressive power conversion efficiency (PCE) of 6.4% was reported using poly [2,6-(4,4′-dihexyl-4H-cyclopenta[2,1-b; 3,4-b′]dithiophene-alt-N-alkylthieno [3,4-c]pyrrole-4,6-dione (PCPDT-TPD, Figure 1). [40][41][42][43] The strong electron-accepting ability of the TPD unit is derived from the presence of two carbonyl groups, lowering the energy of the highest occupied molecular orbital (HOMO) levels.…”

“…5,7,23,36,37,[40][41][42][43] Despite the facts that the formation of aryl-aryl bonds is typically wellcontrolled and the yields in the elementary reactions are generally high, these coupling reactions possess several drawbacks: (i) numerous steps are required in monomer synthesis, (ii) the organometallic functional groups are unstable, (iii) the reactions result in the formation of stoichiometric amounts of toxic byproducts. On the other hand, direct C-H arylation polymerization has attracted much attention because it presents an economically and ecologically attractive alternative to the traditional cross-coupling reactions.…”

Alkyl side-chain branching point effects in thieno[3,4-c]pyrrole-4,6-dione copolymers

“…Use of a bi(alkyl)thiophene aids solubility, though the tail-totail configuration of the alkyl chains is vital in preserving crystallinity. [21] Such alkylated TPD-2T polymers have achieved efficiencies as high as 7.3% in BHJ photovoltaic cells and field-effect transistors exhibit hole mobilities as high as 0.6 cm 2 /V s. [22][23][24][25][26][27] In addition, these polymers have recently been reported with both economic and green syntheses. [28,29] Here, we report a novel and efficient synthesis of the TPD unit facilitating late-stage alkylation by haloalkanes and direct C-H activation polymerisation.…”