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Full paper
E-beam evaporated Nb
2
O
5
as an effective electron transport layer for large
flexible perovskite solar cells
Jiangshan Feng
a
, Zhou Yang
a,
⁎
, Dong Yang
a
, Xiaodong Ren
a
, Xuejie Zhu
a
, Zhiwen Jin
a
, Wei Zi
a
,
Qingbo Wei
a
, Shengzhong (Frank) Liu
a,b,⁎⁎
a
Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education; Shaanxi Key Laboratory for Advanced Energy Devices; Shaanxi
Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119, China
b
Dalian National Laboratory for Clean Energy; iChEM, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
ARTICLE INFO
Keywords:
Perovskite
Solar cell
e-beam evaporation
Flexible
ABSTRACT:
E-beam evaporated Nb
2
O
5
film is directly used as an effective electron transport layer (ETL) for perovskite solar
cells without needing any posttreatment. The effect of Nb
2
O
5
thickness on optical and electronic properties of
the perovskite layer deposited thereupon are studied in detail. It is found that 60 nm thick Nb
2
O
5
ETL delivers
the best photovoltaic performance with PCE as high as 18.59%. In particular, e-beam evaporated Nb
2
O
5
is
found to be advantageous in large area flexible perovskite solar cells, with larger area cells showing comparable
Jsc and Voc values as smaller area devices, and the PCE loss is mainly caused by increased series resistance
leading to reduced FF. With proper cell design to limit the resistance and associated FF loss, it is expected that
the large area cells should present respectable FF and PCEs as their smaller area devices.
1. Introduction
In 2009, Prof. Miyasaka group first used perovskite as sensitizer in
dye-sensitized solar cells, which brought the lead halide perovskite into
the solar cell research. Due to the corrosion of perovskite in electrolyte,
the devices can just work for a short time [1]. A big leap happened in
2012, Park group replaced electrolyte with solid state hole transport
material. Both the power conversion efficiency(PCE) and stability of
perovskite solar cell has been increased [2]. From then on, perovskite
solar cells have attracted tremendous attention. The PCE of the
perovskite solar cells has rapidly soared from 3.8% to over 22% in just
seven years [3–7]. The prestigious performances are attributed to their
excellent opto-electronic properties, such as long carrier life time [8],
larger and balanced hole, electron mobility [9], and intrinsic low trap
density [10,11], which make them as great candidates for LED, laser,
photodetector device [12].
Generally, a perovskite solar cell contains five major components,
namely transparent conductive oxide (TCO), electron transport layer
(ETL), perovskite absorber, hole transport layer (HTL) and metal
electrode. The perovskite solar cell is often classified into two basic
types (1) mesoscopic structure uses mesoporous semiconducting
materials such as TiO
2
[13], ZnO [14],WO
3
[15] as ETL or mesoporous
insulator like Al
2
O
3
[16] as scaffold; (2) planar structure implements
ultra-thin compact layer such as TiO
2
[17,18],WO
3
[19], SnO
2
[20] for
ETL and PEDOT: PSS [21], NiO [22,23], CuSCN [24], carbon nanotube
[25] for hole transport layers (HTLs). Due to its easy fabrication, planar
structured cell design appears to be more popular. To assemble a
planar type perovskite solar cell, a light harvesting perovskite layer is
sandwiched in between the ETL and the HTL that are used as carrier-
selective media to collect photogenerated electrons and holes, respec-
tively. Up to now, the PCE of the planar type solar cell shows very
similar PCE comparing to that of the mesoporous structured cell using
TiO
2
ETL. Recently, more and more research efforts have been directed
to develop large area solar cells, particularly flexible devices [26], for
which large area ETL, HTL and perovskite film with good uniformity
has become a prerequisite. Liu et al. reported ZnO nanoparticle as ETL
in flexible perovskite solar cell for 10.0% efficiency [27]. However, ZnO
is found to accelerate decomposition of MAPbI
3
and therefore not
suitable for practical application [28,29]. By utilizing colloidal Nb-
doped TiO
2
nanocrystal coupled with UV treatment, perovskite solar
cells with a low temperature processed electron transport layer have
achieved PCEs of 19.57% and 16.01% on rigid and flexible substrates,
respectively [30]. Using doped NiO, Han et al. developed a very stable
perovskite cell with efficiency as high as 15% [31] on glass substrate.
http://dx.doi.org/10.1016/j.nanoen.2017.04.010
Received 10 January 2017; Received in revised form 12 March 2017; Accepted 5 April 2017
⁎
Corresponding author.
⁎⁎
Corresponding author at: Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education; Shaanxi Key Laboratory for Advanced Energy Devices; Shaanxi
Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119, China.
E-mail addresses: zyang@snnu.edu.cn (Z. Yang), liusz@snnu.edu.cn (S.F. Liu).
Nano Energy 36 (2017) 1–8
Available online 06 April 2017
2211-2855/ © 2017 Published by Elsevier Ltd.
MARK