posted on 2021-01-19, 20:05authored byJin-Woo Lee, Nayoun Choi, Dongjun Kim, Tan Ngoc-Lan Phan, Hyunbum Kang, Taek-Soo Kim, Bumjoon J. Kim
The recent evolution of new polymer
acceptors (PAs)
using small-molecule building blocks with high light absorption has
significantly increased the power conversion efficiency (PCE) of all-polymer
solar cells (all-PSCs), but their mechanical properties are typically
poor. Thus, poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] (N2200) is still
considered one of the most successful PAs in all-PSCs.
Herein, we report the development of new naphthalene dimide-based
PAs (NDI-PAs) that enable the achievement of
both superior PCEs and mechanical robustness of all-PSCs compared
to those of N2200-based devices. Our approach is very simple and effective
for constructing a series of PAs [PNDIHD/DT-x, where x = 0–1], consisting of two NDI units
with different side chains (2-hexyldecyl (HD) and 2-decyltetradecyl
(DT)). The PNDIHD/DT-0.41-based all-PSCs with the poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))]
(PBDB-T) polymer donor achieve a PCE of 9.3%, which outperforms the
N2200-based device (PCE = 7.7%). This is mainly attributed to the
enhanced charge generation and transport abilities of the PNDIHD/DT-0.41-based
all-PSCs, as a result of optimal domain size and purity as well as
high electron mobility. Importantly, the PBDB-T:PNDIHD/DT-0.41 blend
shows excellent mechanical robustness, with a crack onset strain (COS)
of 30% and a toughness of 7.5 MJ m–3. In addition,
a flexible polymer solar cell (FPSC) device with the PBDB-T:PNDIHD/DT-0.41
blend shows a high initial PCE of 6.73%, which is maintained over
6% even after bending 1500 times.