Synthesis of naphtho[1,2-d:5,6-d']bis([1,2,3]triazole)-based wide-bandgap alternating copolymers for polymer solar cells and field-effect transistors

The development of wide bandgap p-type conjugated polymers to pair with low bandgap nonfullerene n-type acceptors (NFAs) has emerged as an important topic in polymer solar cells. Naphtho[1,2-d:5,6-d’]bis([1,2,3]triazole (NTz), in which the central nitrogen bears an aliphatic side chain, can serve as a mild electron acceptor to generate wide bandgap p-type conjugated polymers. To this end, we synthesized two donor-acceptor alternating copolymers, PBDTNTz1 and PBDTNTz2, based on naphthobistriazole (NTz) as the acceptor and benzodithiophene (BDT) as the donor. The two polymers had optical bandgaps of ca. 1.9 eV with absorption spectra complementary to that of the typical nonfullerene n-type acceptor ITIC. Side-chain engineering was implemented by introducing different combinations of alkyl groups on the BDT and NTz units in PBDTNTz1 and PBDTNTz2. According to theoretical calculations, PBDTNTz1 has higher backbone coplanarity with a face-on π-π stacking orientation. Consequently, a device with the PBDTNTz1:ITIC combination delivered a high PCE of 7.37% with a V_oc of 0.94 V, a J_sc of 14.04 mA/cm² and an FF of 55.8%. In addition, organic field-effect transistors (OFETs) using PBDTNTz1 and PBDTNTz2 exhibited hole mobilities of 2.2 × 10⁻² cm²V⁻¹s⁻¹ and 5.0 × 10⁻² cm²V⁻¹s⁻¹ with on/off ratios of 1 × 10⁴ and 9 × 10², respectively.