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Portions of this work were performed by the Planetary Science
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Materials and Methods
Figs. S1 to S18
Tables S1 to S4
References ( 27–89)
31 July 2016; accepted 23 November 2016
Published online 15 December 2016
Highly stretchable polymer
semiconductor films through the
Jie Xu,1 Sihong Wang,1 Ging-Ji Nathan Wang,1 Chenxin Zhu,2 Shaochuan Luo, 3
Lihua Jin, 4, 5 Xiaodan Gu,1, 6† Shucheng Chen,1 Vivian R. Feig, 7 John W. F. To,1
Simon Rondeau-Gagné,1‡ Joonsuk Park, 7 Bob C. Schroeder,1§ Chien Lu,1 Jin Young Oh,1
Yanming Wang, 7 Yun-Hi Kim, 8 He Yan, 9 Robert Sinclair, 7 Dongshan Zhou, 3 Gi Xue, 3
Boris Murmann,2 Christian Linder, 5 Wei Cai, 4 Jeffery B.-H. Tok,1
Jong Won Chung,1, 10|| Zhenan Bao1||
Soft and conformable wearable electronics require stretchable semiconductors, but
existing ones typically sacrifice charge transport mobility to achieve stretchability. We
explore a concept based on the nanoconfinement of polymers to substantially improve the
stretchability of polymer semiconductors, without affecting charge transport mobility.
The increased polymer chain dynamics under nanoconfinement significantly reduces the
modulus of the conjugated polymer and largely delays the onset of crack formation under
strain. As a result, our fabricated semiconducting film can be stretched up to 100% strain
without affecting mobility, retaining values comparable to that of amorphous silicon. The
fully stretchable transistors exhibit high biaxial stretchability with minimal change in
on current even when poked with a sharp object. We demonstrate a skinlike finger-wearable
driver for a light-emitting diode.
Electronics for biomedical applications, such as physiological monitoring (1), implanted treatment (2), electronic skins ( 3), and human- machine interface ( 4), must be mechani- cally compatible with biological tissues, with
characteristics of low modulus, flexibility, and
stretchability. Several approaches based on geo-
metric designs, such as buckles ( 5), wavy patterns
(1, 2), and kirigami ( 6), impart stretchability to
electronics and have the potential for a variety
of wearable applications. Stretchable electronics
based on intrinsically stretchable materials may
enable scalable fabrication, higher device den-
sity, and better strain tolerance but remain scarce
owing to the lack of high-performance stretchable
semiconductors that possess both high mechani-
cal ductility and high carrier mobility at large
strains. Although some nanomaterial systems
[such as two-dimensional (2D) materials] pos-
sess moderate stretchability (below 20% strain)
with good electrical performance ( 7), their rigid
nature has limited device density, mechanical
robustness, and wide applicability.
Conjugated polymers have been developed as
a softer semiconductor with high charge carrier
mobilities rivaling that of poly-Si ( 8–10), but their
stretchability remains poor. Molecular design rules
( 11–14) that are effective in improving stretch-
ability often result in a decrease in mobility.
Nanowire and nanofibril networks ( 15, 16) and
microcracked films ( 17) improved strain toler-
ance, but the materials used were already known
to be ductile ( 18) and had low mobilities. More
recently, high-performance but brittle conjugated
polymers have been afforded improved stretch-
ability through blending with a ductile lower-
performance conjugated polymer ( 19). However,
the films still have limited ductility due to the
unchanged polymer chain packing and dynamics.
Nanoconfinement of polymers into nanometer-scale dimensions is known to result in peculiar
thermodynamic and kinetic properties due to
the finite-size effect and the interface effect.
Nanoconfinement can alter many polymer physical properties, including lowering the mechanical
modulus ( 20) and glass transition temperature
( 21) and increasing the mechanical ductility
( 22). These changes have been attributed to the
enhanced polymer chain dynamics in the amorphous regions ( 23, 24) and the restricted growth
of large crystallites ( 25), and these are all desirable for stretchable materials. Therefore, we
hypothesized that the increased polymer chain
dynamics and suppressed crystallization from
nanoconfinement may increase the mechanical
stretchability of high-mobility, less ductile polymer
Nanoconfinement of polymer semiconductor
is achieved by forming nanofibrils inside a soft,
1Department of Chemical Engineering, Stanford University,
Stanford, CA 94305, USA. 2Department of Electrical
Engineering, Stanford University, Stanford, CA 94305, USA.
3Department of Polymer Science and Engineering, School of
Chemistry and Chemical Engineering, Nanjing University,
Nanjing 210093, China. 4Department of Mechanical
Engineering, Stanford University, Stanford, CA 94305, USA.
5Department of Civil and Environmental Engineering, Stanford
University, Stanford, CA 94305, USA. 6Stanford Synchrotron
Radiation Lightsource, SLAC National Accelerator Laboratory,
Menlo Park, CA 94025, USA. 7Department of Materials Science
and Engineering, Stanford University, Stanford, CA 94305,
USA. 8Department of Chemistry and RINS, Gyeongsang
National University, Jinju 660-701, South Korea. 9Department
of Chemistry and Hong Kong Branch of Chinese National
Engineering Research Center for Tissue Restoration &
Reconstruction, The Hong Kong University of Science and
Technology, Clear Water Bay, Kowloon, Hong Kong. 10Samsung
Advanced Institute of Technology Yeongtong-gu, Suwon-si,
Gyeonggi-do 443-803, South Korea.
*These authors contributed equally to this work. †Present address:
School of Polymer Science and High Performance Materials,
University of Southern Mississippi, Hattiesburg, MS 39402, USA.
‡Present address: Department of Chemistry and Biochemistry,
University of Windsor, Windsor, Ontario N9B 3P4, Canada. §Present
address: Materials Research Institute and School of Biological and
Chemical Sciences, Queen Mary University London, Mile End Road,
London E1 4NS, UK. ||Corresponding author. Email: zbao@
stanford.edu (Z.B.); email@example.com (J. W.C.)