Diketopyrrolopyrrole-Based Conjugated Polymer Entailing Triethylene Glycols as Side Chains with High Thin-Film Charge Mobility without Post-Treatments

Abstract

Side chain engineering of conjugated donor-acceptor polymers is a new way to manipulate their optoelectronic properties. Two new diketopyrrolopyrrole (DPP)-terthiophene-based conjugated polymers PDPP3T-1 and PDPP3T-2, with both hydrophilic triethylene glycol (TEG) and hydrophobic alkyl chains, are reported. It is demonstrated that the incorporation of TEG chains has a significant effect on the interchain packing and thin-film morphology with noticeable effect on charge transport. Polymer chains of PDPP3T-1 in which TEG chains are uniformly distributed can self-assemble spontaneously into a more ordered thin film. As a result, the thin film of PDPP3T-1 exhibits high saturated hole mobility up to 2.6 cm² V^-1 s^-1 without any post-treatment. This is superior to those of PDPP3T with just alkyl chains and PDPP3T-2. Moreover, the respective field effect transistors made of PDPP3T-1 can be utilized for sensing ethanol vapor with high sensitivity (down to 100 ppb) and good selectivity.

Keywords: charge carrier mobility; conjugated donor–acceptor polymer; diketopyrrolopyrrole; side chains; triethylene glycol.

Scheme 1

Chemical structures of PDPP3T‐1, PDPP3T‐2, and PDPP3T and illustration of the design rationale for incorporation of TEG side chains in the conjugated polymers.

Scheme 2

Synthetic routes to PDPP3T‐1 and PDPP3T‐2. Reagents and conditions: (i) K₂CO₃, N,N‐Dimethylformamide (DMF), 130 °C, 36 h; (ii) N‐bromosuccinimide, CHCl₃, r.t., 4 h; (iii) Pd₂(dba)₃, P(o‐tol)₃, toluene, 100 °C, 36 h.

Figure 1

The transfer and output characteristics of a,d) as‐prepared PDPP3T‐1 based FETs, b,e) PDPP3T‐2, and c,f) PDPP3T based FETs after thermal annealing at 100 °C (V _DS for transfer characteristics is −80 V).

Figure 2

Flash DSC thermograms of a) PDPP3T‐1, b) PDPP3T‐2, and c) PDPP3T. GIWAXS patterns of the d–f) as‐prepared and g–i) thermally annealed thin‐films of d,g) PDPP3T‐1, e,h) PDPP3T‐2, and f,i) PDPP3T.

Figure 3

a) Transfer characteristics for PDPP3T‐1 FETs after exposure to different concentrations (0–100 ppm) of ethanol vapor. b) I _DS versus time under 1 ppm ethanol vapor and air (inset). c) Variation of the drain current for FET of PDPP3T‐1 after exposure to different gas vapors: 1, CO₂ (pure); 2, CH₂Cl₂ (3 010 000 ppm); 3, hexane (20 000 ppm); 4, ethyl acetate (1000 ppm); 5, acetone (100 ppm); 6, acetone (1 ppm); 7, C₂H₅OH (1 ppm); and 8, C₂H₅OH (10 000 ppm) to PDPP3T under the same conditions.