Synthesis and photovoltaic properties of benzo[1,2-b:3,4-b
0
]
thiophene-based conjugated copolymers with a pendent acceptor
Tao Jia
•
Qiong Hou
•
Kang Xiong
•
Qi Li
•
Lintao Hou
Received: 2 January 2014 / Accepted: 30 January 2014 / Published online: 15 February 2014
Ó Springer Science+Business Media New York 2014
Abstract Two novel benzo[1,2-b:3,4-b
0
]thiophene-based
copolymers (namely, PBDT-TPABTBn and PBDT-BTCz)
with a pendent acceptor were synthesized through Pd-cat-
alyzed Stille coupling reactions for use in organic photo-
voltaic devices. To study the photovoltaic properties of the
resulting copolymers, polymer solar cells were fabricated
with the copolymers as electron donors and [6,6]-phenyl-
C
71
-butyric acid methyl ester as an electron acceptor. The
obtained devices based on PBDT-TPABTBn and PBDT-
BTCz exhibited power conversion efficiencies of 1.62 %
(V
oc
= 0.94 V, J
sc
= 4.74 mA cm
-2
, FF = 0.39) and
0.95 % (V
oc
= 0.64 V, J
sc
= 4.16 mA cm
-2
, FF = 0.36),
respectively. Results indicated that the two copolymers
were the promising donor candidates for polymer solar cell
applications.
1 Introduction
Many researchers focus on organic solar cells (OSCs)
because of their low cost, light weight, flexibility, easy
fabrication, and solution processing [1–6]. Solution-pro-
cessed bulk heterojunction (BHJ) polymer solar cells
(PSCs) might be good candidates for the next generation of
photovoltaic device because of their various advantages,
such as excellent mechanical property that is related
to small molecule solar cells (SMSCs) with easy
crystallization and poor film formation [7, 8]. Using
functional layers for buffering, charge transportation,
optical spacing, morphology modification of photoactive
film with post-annealing, solvent-drying, and additive
processing, the power conversion efficiencies (PCEs) of
single- junction BHJ solar cells has increased substantially
[9–11]. However, PSCs were still inferior to its inorganic
counterparts in terms of PCEs and stability [12]. As a
principal factor, designing BHJ composites with a broad
absorption response in the solar spectrum to effectively
harvest the solar photon was one of the most efficient
approaches to obtain higher PCEs. Therefore, narrow
bandgap polymer developments by featuring alternating
electron-rich (donor, D) and electron-deficient (acceptor,
A) units have attracted continuous intensive research [13,
14]. Among the various conjugated polymers, benzo[1,2-
b:4,5-b
0
]di-thiophene (BDT), which is a promising com-
mon unit for photovoltaic conjugated polymers, has been
widely used as an electron-donating unit because of its
planar and rigid fused aromatic ring. This structure is
helpful in strengthening interactions and charge-transpor-
tations among polymers [15–18]. By the structural modi-
fication with thienyl side chains on the BDT skeleton,
many copolymers of excellent performance have been
designed and synthesized for higher efficiency [19].
According to numerous previous studies [20], pendent
acceptor introduction in the copolymers can produce a low-
lying lowest unoccupied molecular orbital (LUMO) level,
as well as a relatively low bandgap. In addition, the devices
that exhibit high J
sc
and V
oc
values might be available [21,
22]. In our previous works [23–25], a series of random
copolymers derived from fluorene unit with pendent D–A
structures on the C9 site has been designed and synthe-
sized. These methods demonstrated that the pendent
acceptor can increase absorption band intensity and favor
T. Jia Q. Hou (&) Q. Li
School of Chemistry and Environment, South China Normal
University, Guangzhou 510006, China
e-mail: houqiong@tom.com; houqiong@scnu.edu.cn
K. Xiong L. Hou
Department of Physics, Jinan University, Guangzhou 510632,
China
123
J Mater Sci: Mater Electron (2014) 25:1639–1646
DOI 10.1007/s10854-014-1777-6