Lowering the bandgap of poly(diketopyrrolopyrrole-alt-terchalcogenophene)s via chalcogen effects for shortwave infrared phototransistors†

Four poly(diketopyrrolopyrrole-alt-terchalcogenophene)s, i.e., ThDPP-Se, ThDPP-Te, SeDPP-Se and SeDPP-Te, were synthesized via Stille polycondensation of thiophene- or selenophene-flanked diketopyrrolopyrrole C–Br monomers and bistannyl reagents of selenophene or tellurophene. Absorption spectra gradually red-shifted from ThDPP-Se to SeDPP-Te, owing to the chalcogen effects. The polymer SeDPP-Te exhibited strong absorption in the shortwave infrared (SWIR) region with the absorption maximum above 1000 nm. All four polymers are p-type semiconductors with hole mobility higher than 1.5 cm² V⁻¹ s⁻¹, as extracted from top-gate and bottom-contact organic thin-film transistors (OTFTs). Bottom-gate and top-contact phototransistors (OPTs) were fabricated with SeDPP-Te:[6,6]-Phenyl C61 butyric acid methyl ester (PC₆₁BM) blends as semiconducting layers. The best device performance was achieved using 20 mol% PC₆₁BM blended with SeDPP-Te. Under the irradiation of 1030 nm SWIR light, OPTs exhibited photoresponsivity (R) up to 34.92 A W⁻¹, photosensitivity (P) up to 30.97, and specific detectivity (D*) up to 2.76 × 10¹¹ Jones.