Figure 3 (a) Solubility
of PNTB-Cl and PNTB6-Cl in chloroform after stirring for 24 h; (b) The
absorption spectra of polymer pure films under different conditions (c)
Schematics of LBL deposition; (d) Illustration of film morphology washed
by chloroform and N3 penetration between polymer domains. Reproduced
with permission.[16] Copyright 2021, The Royal
Society of Chemistry.
Wu et al. [33] further developed a NTI-based
polymer PNTB-HD by employing a linear chain in NTI. The PNTB-HD
exhibited a stronger aggregation tendency in chloroform solution, which
leads to higher hole mobility, better phase separation and favorable
morphology of blend films. Therefore, the PNTB-HD:N3-based OSCs
exhibited an optimized PCE of 18.15 %, which is much higher
than 16.77 % and 16.28 % for PNTB-2T:N3 and PM6:N3. Importantly, the
PNTB-HD: N3 device also exhibited much better thermal stability with
82.9 % of initial efficiency maintained under continuous heating at 65
°C (Figure 4). The single crystal of NTIs with butyl and ethylhexyl
substitutions provide some information to understand how the alkyl
chains in NTI impact on physical properties of polymers. In NTI-EH, the
distances of 2.72 and 2.67 Å between C=O and H-C were observed. However,
interactions between C=O with H-C in NTI-Bu are much stronger and their
distances of 2.49 and 2.55 Å are much shorter. He groups synthesized two
polymers (PNTB-OAc and PNTB-OH) by introducing hydroxy (OH) or acetoxy
(OAc) groups into the NTI unit.[69] Compared to
the hydroxy group, the acetoxy group makes NTI-OAc have more regular
hydrogen bonds and the polymer PNTB-OAc show ordered packing and
stronger crystallinity. The PNTB-OAc:N3-based Q-PHJ OSCs achieved a much
higher PCE of 16.53 %, while PCE for PNTB-OH is only 6.79 %.
Additionally, the PNTB-OAc:N3-based Q-PHJ OSCs also deliver superior
photostability and storage stability. He groups introduced a
hydroxylated BTIC-OH-δ as a bifunctional layer in Q-PHJ
film.[70] The inserted BTIC-OH-δ layer effectively
protected the donor layer from the erosion of the chloroform solution,
complemented the light absorption and formed cascade energy levels
between the initial donor and an acceptor in a Q-PHJ device. The
PNTB-HD: N3-based Q-PHJ OSCs treated with a BTIC-OH-δ molecular layer
achieved a high PCE of 17.33 %, the corresponding semi-transparent
device also achieved a PCE of 13.44 % with AVT of 23.62 %.