Synthesis and study of low-bandgap polymers containing the diazapentalene and diketopyrrolopyrrole chromophores for potential use in solar cells and near-infrared photodetectors

The two pairs of structurally related donor–acceptor polymers (P1–P4) derived from diketopyrrolopyrrole (DPP) and diazapentalene (DAP) building blocks were synthesized and compared for their optical and photovoltaic properties with potential applications in solar cells and near-infrared (NIR) photodetectors. Having the electron-rich fluorene and bis(2′-thienyl)pyrrole (TPT) units as donors, the synthesized donor–acceptor polymers have band gap levels in the range 1.22–1.79 eV. The solar cells based on the blend of P2 (DPP–TPT polymer) and PC71BM exhibited the best performance, showing a Voc of 0.61 V, Jsc of 10.38 mA cm−2, FF of 0.44 and PCE of 2.8%. The photodetector based on the NIR-absorbing P4 (DAP–TPT polymer) displayed a good photovoltaic response over a wide spectral range of 400–1100 nm and an EQE of 13% and detectivity of 2.3 × 1010 Jones at 800 nm.