A Tetrathienopyrrole-Based Ladder-Type Donor Polymer for Wavelength-Selective Organic Near-Infrared Cavity Detectors.

Incorporation of compact spectroscopic near-infrared (NIR) light detectors into various wearable and handheld devices opens up various new applications, such as on-the-spot medical diagnostics. To extend beyond the detection window of silicon, i.e., past 1000 nm, organic semiconductors are highly attractive because of their tunable absorption. In particular, organic NIR wavelength-selective detectors have been realized by incorporating donor:acceptor thin films, exhibiting weak intermolecular charge-transfer (CT) absorption, into an optical microcavity architecture. In this work, a new ladder-type donor polymer, based on an extended dithienopyrrole unit, is investigated in blends with PC61BM as the acceptor. It is shown that extending the rigid backbone enhances the CT absorption and extends the detection range further into the NIR. This results in a full-width-at-half-maximum of 32-40 nm at wavelengths between 920 and 1450 nm, yielding detectivities in the range of 1.07 × 10^12 to 1.82 × 10^10 Jones, thereby outperforming the state-of-the-art PBTTT-based devices, both in terms of absorption range as well as efficiency.