The Fabrication of Ordered Bulk Heterojunction Solar Cell by Nanoimprinting Lithography Method Using Patterned Silk Fibroin Mold at Room Temperature
Ding et al. Nanoscale Research Letters
The Fabrication of Ordered Bulk Heterojunction Solar Cell by Nanoimprinting Lithography Method Using Patterned Silk Fibroin Mold at Room Temperature
Guangzhu Ding 0
Qianqian Jin 0
Qing Chen 0
Zhijun Hu
Jieping Liu 0
0 College of Chemistry and Materials Science, Huaibei Normal University , Huaibei 235000 , China
The performance of organic solar cell is greatly determined by the nanoscale heterojunction morphology, and finding a practical method to achieve advantageous nanostructure remains a challenge. We demonstrate here that ordered bulk heterojunction (OBHJ) solar cell can be fabricated assisted by a simple, cost-effective nanoimprinting lithography method using patterned silk fibroin film mold at room temperature. The P3HT nanogratings were achieved by nanoimprinting lithography (NIL) process, and phenyl-C61-butyric acid methyl ester (PCBM) was spin-coated on the top of P3HT nanogratings. The conducting capacity of P3HT nanograting film has little difference compared with the unimprinted film in the vertical direction, due to the same edge-on chain alignment. However, it can be found that the fabrication of OBHJ nanostructure using room temperature NIL technique with patterned silk fibroin mold is able to promote optical absorption, interfacial area, and bicontinuous pathway. Therefore, the ordered heterojunction morphology plays an important part in improving device performance due to efficient exciton diffusion, dissociation, and reducing charge recombination rate.
Nanoimprint lithography; Nanopattern; Ordered bulk heterojunction; Silk fibroin film
Background
The organic solar cells based on the bulk
heterojunction (BHJ) have received considerable attention as an
attractive alternative to silicon photovoltaic cell as they
have achieved favorable characteristics, such as low
cost, flexibility, and simple process [
1, 2
]. As long as
there is light absorption, the excitons are generated,
diffused, and dissociated at the interface between donor
and acceptor materials and then transported to their
respective electrodes, forming the external circuit [3].
Therefore, the performance of organic solar cell is greatly
determined by the nanoscale heterojunction morphology
within active layer. One of the ideal structures in active
layer is to construct an ordered bulk heterojunction (OBHJ)
morphology consisting of vertically bicontinuous and
interdigitized heterojunction between donor and
acceptor materials, to enable both efficient exciton
separation and transport [
4–6
].
Despite OBHJ nanostructure morphology contributes
to the solar cell performance and a comprehensive
understanding of fundamental principle, finding a
practical method to achieve this nanostructure remains a
challenge to now. Several techniques, such as polymer
nanowires, block copolymer, and nanoimprinting
lithography (NIL), have been reported to fabricate OBHJ
solar cell [
7–9
]. Among these techniques, thermal NIL is
investigated as a promising method to define
nanostructures due to its high resolution, effective cost, and simple
process [
10, 11
]. NIL method is able to replicate the
nanostructures defined on a hard mold into some soft materials,
such as semiconducting polymers [
12–19
], ferroelectric
polymers [
20, 21
], and proteins [
22, 23
]. Therefore, the
control of nanoimprint mold is of great importance in the
fabrication of OBHJ solar cell by NIL technique. Some
traditional molds with high resolution over a large area,
such as silicon mold or anodic aluminum oxide mold,
are reported to apply; however, they are usually
timeconsuming, have complicated process, have simple
fragility, crush or deformed easily, and do not to meet the
need of commercial application. It is desired to seek a
costeffective and simple process method for mold fabrication.
Silk fibroin film from the Bombyx mori silkworm has
attracted considerable interest owing to its biological,
mechanical, and optical properties [
24–27
]. Silk fibroin film
is able to be easily patterned by several techniques [
22, 28
]
and has been applied to biocompatible and degradable
electronic or photonic devices [
29, 30
]. In nanoimprinting
process, the application of heat and pressure to a patterned
silk fibroin mold, which is fabricated by control of the
water content and beta sheet crystallinity within silk film,
can be accomplished to transfer nanostructure to other soft
materials [23]. Silk fibroin film was chosen for the
nanoimprinting mold mainly due to its advantageous material
properties as well as simple and inexpensive production
process [
31, 32
]. The Bombyx mori silkworm which is
used to produce patterned silk fibroin film comes from
broad source and is cheap. Silk fibroin film is able to be
easily patterned, and the fabrication process is simple and
convenient, fully meet to the demand of large area
production. Then, there is little interaction between silk
film and conjugated polymer, for example, p (...truncated)