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.