Energy & Environmental Science: Volume 8 Number 3 March 2015 Pages 677-1048
Energy & Environmental Science: Volume 8 Number 3 March 2015 Pages 677-1048
Energy & Environmental Science: Volume 8 Number 3 March 2015 Pages 677-1048
Environmental
Science
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ISSN 1754-5692
PAPER
Sangwook Lee, Hyun Suk Jung et al.
Highly efficient and bending durable perovskite solar cells: toward a
wearable power source
Energy &
Environmental
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PAPER
mm. Degradation of the device performance by the bending was the result of crack formation from the
transparent conducting oxide layer, demonstrating the potential of the low-temperature-processed TiOx
DOI: 10.1039/c4ee02441a
layer to achieve more ecient and bendable perovskite solar cells, which becomes closer to a practical
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Broader context
Perovskite solar cells, based on state-of-the-art inorganicorganic halide perovskite materials, are one of the most promising devices for realizing a wearable power
source, on account of their high energy conversion eciency, and economic fabrication processes such as roll-to-roll printing. Therefore, recently, the main concern of
research in this eld has moved to fabricating a highly exible device, while preserving the high eciency. The key process to achieve such a kind of highly ecient and
exible perovskite solar cells is the oxide lm deposition process to make compact-electron-collection layers at a low temperature. In this regard, we report on highly
ecient (12.2%) and bending durable perovskite solar cells on a cheap polyethylene naphthalate (PEN) substrate, with a TiOx compact-electron-collection layer that is
fabricated at below 80 C using the plasma enhanced atomic layer deposition method. We observed constant device performance up to 1000 bending cycles with 10
mm of bending radius. This study demonstrates that the exible perovskite solar cell is potentially used for a power solution of future wearable devices.
1. Introduction
Paper
have shown the possibility of higher eciency than that displayed by organic exible solar cells.8 The reported exible
perovskite solar cells have employed two types of light
absorbers, i.e. CH3NH3PbI3 and CH3NH3PbI3xClx.811 So far,
the best PCE of the exible perovskite solar cells has been
10.2%, obtained by using a 300 nm-thick CH3NH3PbI3 layer,9
however, this is still inferior to the rigid-type perovskite solar
cells. The main reasons for the relatively low performance are
the large series resistance and fast charge recombination, which
are expected to be improved by optimizing the TiO2 or ZnO
compact charge collection layer in the exible substrate.8,9
Usually, a few tens of nanometer-thick, solution-processed,
TiO2 thin lm as the compact layer can produce excellent
performance when it is baked at over 500 C.8,12,13 However, for
exible devices, the high temperature processes need to be
avoided. Therefore, it is extremely important to study the origin
of the inadequate properties of the low-temperature-processed
compact nanolayers, and to establish the optimal technology
for their development. Moreover, observation of the bending
fatigue of the exible perovskite solar cells, which has not been
reported to date, is also crucial for real-world application and
commercialization of the exible solar cells.
Here, we present highly bendable (up to 1 mm of bending
radius) and extremely ecient (PCE 12.2%) perovskite solar
cells based on tin-doped indium oxide (ITO) on PEN exible
substrates by forming an approximately 20 nm-thick TiOx
compact layer on the substrate at 80 C via plasma enhanced
atomic layer deposition (PEALD). Moreover, we investigate the
bending stability of the devices, with three eective bending
radii for the wearable devices: 400 mm (R400), 10 mm (R10), and
4 mm (R4) for human neck, wrist, and nger, respectively. The
device performance can withstand up to 1000 cycles of the
bending test for R400 and R10. However, in the case of R4, the
PCE signicantly deteriorates to 50% of the initial eciency
aer 1000 cycles. We demonstrate that the origin of degradation
is not the fracture in the perovskite layer but is rather due to the
fracture in the transparent conducting oxide layer (ITO in this
study) on the PEN substrate, by analysing the microstructure of
the damaged PEN/ITO/TiOx/perovskite multilayer aer the
bending test.
2.
Fig. 2 (a) Cross-sectional TEM (a-1 and a-2), scanning TEM (a-3) and
EDS mapping (a-4 and a-5) images of Lt-ALD-TiOx on the ITO
substrate. Scale bar: 100 nm (a-1), 10 nm (a-2 and a-3), and 25 nm (a-4
and a-5). (b) Average JV characteristics of the exible devices with
dierent TiOx layers. (c) TRPL trace at 770 nm with 670 nm excitation.
The TRPL trace could be clearly distinguished from the instrumental
response function. Average life times were convoluted to be 383 ns,
435 ns, and 537 ns respectively in the dierent TiOx layers. All the
convoluted parameters are listed in Table S2. See the ESI for details.
(d) Nyquist plots of each exible perovskite solar cell in the opencircuit state. The low Z region (red squared) is magnied in the inset.
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4. Experimental
4.1. Materials
Ethanol and 1-butanol were purchased from Dychemi and
Tokyo Chemical Industry, respectively. Nitric acid (HNO3) was
purchased from Junsei Chemical. Spiro-MeOTAD was
purchased from the Luminescence Technology Corp. The other
materials were purchased from Sigma-Aldrich. All materials
were used as received. CH3NH3I was prepared by synthesizing
according to a previously reported method.13
4.2. Formation of the compact electron collection layer
3.
Conclusions
Paper
Acknowledgements
This work was supported by the Global Frontier R&D Program at
the Center for Multiscale Energy System (2012M3A6A7054861).
Also this work was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education,
Science and Technology (2012M3A7B4049967 and NRF2014R1A4A1008474). Characterization of the crystal structure
and TEM analysis were supported by the Research Institute of
Advanced Materials (RIAM) and XPS analysis was supported by
the National Center for Inter-University Research Facilities
(NCIRF). Especially, this paper is dedicated to our late mentor,
Prof. Kug Sun Hong.