Ding et al. [136] synthesized DPI-based polymer P1 for nonfullerene OSCs. Compared with the thiadiazole in DTBT, the imide is more electron-deficient unit which endows polymer P1 with a deeper HOMO and high V OC (> 0.9 V) value. Moreover, the extended π-conjugation of DPI facilitates polymer packing and charge transport. The best P1:N3 cells gave a PCE of 14.52 %. Zhao et al. [137] synthesized two nonhalogenated DPI-based polymers (pBDTT-DPI-Me and pBDTT-DPI-i Pr) by incorporating different side chains at the N-site of the imide to regulate the polymer’ solubility and aggregation tendency. The pBDTT-DPI-Me showed stronger aggregation than pBDTT-DPI-i Pr in solution. The optimized pBDTT-DPI-Me:Y6-based device showed a PCE of 15.82 %, which is much higher than 11.08 % for pBDTT-DPI-i Pr:Y6. Moreover, the efficiency of the pBDTT-DPI-Me:Y6-based Q–PHJ was further improved to 16.55 % owning to the higher charge carrier mobility, more efficient exciton dissociation, and less charge recombination. Zhanget al. [52] synthesized polymer PBTID which shows a strong and broad absorption, proper aggregation degree, high hole mobility and a deep-lying HOMO level of -5.53 eV. The PBTID:Y6 devices afforded a PCE of 15.8 %.
Sharma and co-workers reported DTID-based polymers P113 and P114.[135] The absorption coefficient, hole transport mobility, and relative dielectric constant of the polymer P114 with fluorine substitutions are higher than that for P113. A PCE of 10.42 % was obtained for P114:ITIC-m based devices, which is higher than that 8.44 % for P113. They also synthesized three polymers to investigated the effect of different donor unit on the optical and electro- chemical properties.[138] Owing to the different electron-donating abilities of donor units, the HOMO energy levels of PDTID-DTS, PDTID-DTB and PDTP-BDT were estimated as -5.37 eV, -5.67 eV, -5.46 eV, respectively. By blending with BThIND-Cl, the PDTID-DTS, PDTID-DTB and PDTP-BDT-based OSCs showed PCE of 14.76 %, 7.22 % and 13.13 %, respectively. They further compared the photovoltaic performance of polymers P135 and P133 which were developed from DPI and DTNI.[42] The P135 showed higher dielectric constant and dipole moment than P133 owing to the stronger electron-withdrawing of DPI. The PSCs based on P135: Y6 exhibited PCE about 15.11 % which is higher than 10.24 % of P133. The DPI-based polymer P106 with 3TB as the donor unit achieved a PCE of 16.49 % in P106:DBTBT-IC:Y18-DMO based ternary OSCs.[139]
Furthermore, there are some other imide-functionalized electron-deficient building blocks that has not been widely used to construct conjugated polymers for application in non-fullerene based OSCs, such as 2,2’-biazulene-1,1’,3,3’-tetracarboxylic diimides (BAzDIs),[140]1,2,5,6-Naphthalenediimide,[141,142] and dithienylbenzodiimide (TBDI),[143] which were synthesized for OFETs and all-PSCs.