Thickness-dependent photovoltaic performance of TiO
2
blocking layer
for perovskite solar cells
Huijing Liu
a
,
b
, Hari Bala
a
,
b
,
*
, Bo Zhang
a
,
b
, BeiBei Zong
a
,
b
, Liwen Huang
a
,
b
,
Wuyou Fu
a
,
b
, Guang Sun
a
,
b
, Jianliang Cao
a
,
b
, Zhanying Zhan
a
,
b
a
School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, People's Republic of China
b
Cultivating Base for Key Laboratory of Environment-friendly Inorganic Materials in University of Henan Province, Henan Polytechnic University, Jiaozuo
454000, People's Republic of China
article info
Article history:
Received 27 August 2017
Received in revised form
6 November 2017
Accepted 7 November 2017
Available online 10 November 2017
Keywords:
Perovskite solar cells
TiO
2
blocking layer
Thickness
Photovoltaic performance
abstract
In this work, organic-inorganic hybrid perovskite solar cells (PSCs) were fabricated under air atmosphere
with high humidity condition around 55%. A modified method was demonstrated for forming the TiO
2
blocking layers (BL-TiO
2
) with various thickness by spin-coating the mixed precursor solutions of ethanol
(CH
3
CH
2
OH), diethanolamine (DEA) and titanium n-butoxide (Ti(OC
4
H
9
)
4
) with different volume ratios
(CH
3
CH
2
OH: DEA: Ti(OC
4
H
9
)
4
¼ 24: 1: R). The thickness of BL-TiO
2
increased from 16 to 54 nm with a rise
of R from 1.5 to 4.0. We demonstrated that suitable thickness of BL-TiO
2
was beneficial to enhancing the
photovoltaic performance of PSCs. The kinetic parameter of electron transport was investigated by the
electrical impedance measurements, and then the influence of BL-TiO
2
thickness on electron transport
performance in PSCs was further discussed. The optimized PSCs delivered a short-circuit photocurrent
density (J
SC
) of 20.61 mA/cm
3
, open-circuit voltage (V
oc
) of 939.4 mV, fill factor of (FF) of 0.661 and overall
conversion efficiency (
h
) of 12.80% when the thickness of BL-TiO
2
was about 31 nm (R ¼ 2.4). The
photovoltaic performance of mesoporous PSCs was extremely dependent on the thickness and
morphology of blocking layer.
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
Organiceinorganic hybrid perovskite materials have drawn
much attention and tremendous research interest since the first
perovskite solar cell was reported in 2009 [1]. Perovskite solar cells
(PSCs) have made such a rapid development mainly owning to its
excellent optical properties including a high absorption coefficient,
suitable band gap and double carriers [2e4]. PSCs are usually
composed of conductive substrate/compact blocking layer (BL)/
mesoporous scaffold layer (optional)/perovskite absorber layer/
hole-transporting layer (HTL)/metal electrode [5,6]. Compact
blocking layer and hole-transporting layer are introduced in PSCs to
separate and collect photogenerated charge that produced in
perovskite absorber layer. The high-quality blocking layer plays a
key role in preventing the charge recombination and rapidly
extracts photoelectrons on the interface of conductive substrate
and perovskite active layer [7]. Compared to zinc oxide and tin
oxide [8e10], TiO
2
is the most frequent blocking-layer material.
Various preparation methods including aerosol spray pyrolysis
[11,12], electrochemical deposition [13], DC-magnetron sputtering
[14], spin coating [15,16], sol-gel method [17] and atomic layer
deposition [18] have been applied for preparation PSCs. With the
advantage of its simple preparation process and low cost, spin
coating method is widely investigated and applied in PSCs.
Although TiO
2
is wide investigated and gets a better achievement,
we need to find a suitable thickness of BL-TiO
2
to bring a positive
effect on the photovoltaic performance of PSCs under air atmo-
sphere with high humidity condition.
Here, we have successfully prepared compact BL-TiO
2
by spin-
coating the precursor solution of mixed CH
3
CH
2
OH, DEA and
Ti(OC
4
H
9
)
4
. We found that the thickness of the BL-TiO
2
could be
controlled by adjusting the volume ratios of the mixed solution,
influencing the photoelectric performance of PSCs. Spin-coating
the colloidal solution (Ti precursor solution) would revamp the
cracking of blocking layer in the subsequent heating process. As-
* Corresponding author.Cultivating Base for Key Laboratory of Environment-
friendly Inorganic Materials in University of Henan Province, Henan Polytechnic
University, Jiaozuo 454000, People's Republic of China.
E-mail address: hari@hpu.edu.cn (H. Bala).
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
https://doi.org/10.1016/j.jallcom.2017.11.081
0925-8388/© 2017 Elsevier B.V. All rights reserved.
Journal of Alloys and Compounds 736 (2018) 87e92