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Solar Energy Materials & Solar Cells
journal homepage: www.elsevier.com/locate/solmat
Efficient PbS QD solar cell with an inverted structure
Weizhe Xu
a
, Furui Tan
a,
⁎
, Qing Liu
a
, Xiansheng Liu
a
, Qiwei Jiang
a
, Ling Wei
a
, Weifeng Zhang
a
,
Zhijie Wang
b
, Shengchun Qu
b
, Zhanguo Wang
b
a
Key Laboratory of Photovoltaic Technique, Department of Physics and Electronics, Henan University, Kaifeng 475004, China
b
Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, China
ARTICLE INFO
Keywords:
Buffer layer
Quantum dot
Solar cell
Inverted structure
ABSTRACT
Efficient PbS quantum dot (QD) solar cell with the traditional structure requires an inorganic buffer layer that is
usually fabricated at high temperature, which is not compatible with the industrially preferential roll-to-roll
fabrication process. Identification of a suitable buffer layer and efficient device construction are thus of
particular significance. Herein, we fabricate PbS quantum dot solar cells in an inverted structure using
poly(thiophene) (3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) as the anode buffer layer.
The resulting devices present a high efficiency of 4.1%, among the best values of inverted PbS QD solar cells.
Electrochemical and photoelectric characterizations have shown that, compared with high-temperature
annealed nickel oxide (NiO) and vanadium pentoxide (V
2
O
5
) layers, the low-temperature processed
PEDOT:PSS layer has a more compatible film properties for efficient injection and collection of charges from
PbS QD active layer. Our work provides a promising strategy for fabrication of QD solar cells in an economical
and efficient way.
1. Introduction
Over the past decade, quantum dot (QD) solar cell has attracted
great attention with its advantage of easy tunability of light response in
a broad range. Because of the notable quantum effects, the energy band
gap can be tuned through adjusting the size of the employed quantum
dots. Lead sulfide (PbS) QD with excitonic Bohr radius of 18 nm shows
great potential for constructing high efficient photovoltaic devices
[1,2]. A Schottky structured solar cell could generate 2% conversion
efficiency while a p-n heterojunction improved the efficiency to above
5% [3–6]. Recently, a certified efficiency as high as 9.9% has been
achieved in molecular halides passivated QD solar cells [7].
As regard to PbS QD solar cell, efficient splitting of excitons in the
built-in field is of particular importance, which requires well performed
electric contact between PbS QD film and the buffer layer. Usually, PbS
QD solar cell employs a traditional device structure in which an n-type
dense film (such as titanium dioxide (TiO
2
) and cadmium sulfide
(CdS)) performs as the cathode buffer, while a p-type film (such as
molybdenum trioxide (MoO
3
)) serves as the anode buffer [8–10].
Although high efficiency was achieved with this device structure, the
fabrication process is not moderate to favor the commercial application
where flexible substrate is preferred. In comparison, an inverted
structure composed of solution processed anode and cathode buffer
layers is more readily employed for moderate and low cost fabrication
process. However, up to now, there are few reported efforts on this
facile but promising device architecture. Tang et al. showed that the
inverted PbS QD solar cell with a Schottky contact would suffer
degradation due to reaction and oxidation at the PbS/electrode inter-
face [3]. Zhao et al. also fabricated a PbS QD device containing a
Schottky contact at the anode and a planar PbS/PCBM heterojunction
contact at the cathode. This structure favored a large FF value after
annealing the device in air [11]. Higher efficiency could be achieved in
the inverted solar cell where a relatively complicated p/n homojunction
contact was employed [12].
In this work, we focus on study of efficient inverted PbS QD solar
cell by adopting three different anode buffer layers. One of the three
films is the commonly used PEDOT:PSS buffer layer that was exten-
sively adopted in the organic, organic/inorganic composite, Si nanos-
tructure-based and hybrid perovskite solar cells [13–16]. Another two
buffer layers, NiO and V
2
O
5
, are also investigated as comparison. After
optimization, the PbS QD solar cell employing PEDOT:PSS and PCBM
as anode and cathode buffer layer respectively show a remarkable
conversion efficiency of 4.1%, which is among the highest values of the
inverted PbS QD solar cells [11,12]. Based on the inverted structure,
the highly efficient PbS QD solar cell is solution-compatible and low-
temperature processable. Our work shed light on QD solar cells with
flexible substrates as well as tandem structures integrating other
materials such as polymer semiconductors or hybrid perovskites.
http://dx.doi.org/10.1016/j.solmat.2016.10.006
Received 13 May 2016; Received in revised form 19 August 2016; Accepted 3 October 2016
⁎
Corresponding author.
E-mail address: frtan@henu.edu.cn (F. Tan).
Solar Energy Materials & Solar Cells 159 (2017) 503–509
0927-0248/ © 2016 Elsevier B.V. All rights reserved.
Available online 12 October 2016
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