Contents lists available at ScienceDirect
Nano Energy
journal homepage: www.elsevier.com/locate/nanoen
A facile molecularly engineered copper (II) phthalocyanine as hole
transport material for planar perovskite solar cells with enhanced
performance and stability
Guang Yang
a,1
, Yu-Long Wang
b,1
, Jia-Ju Xu
b,1
, Hong-Wei Lei
a
, Cong Chen
a
, Hai-Quan Shan
b
,
Xiao-Yuan Liu
b
, Zong-Xiang Xu
b,
⁎
, Guo-Jia Fang
a,
⁎
a
Key Laboratory of Artificial-Micro, and Nano-structures of Ministry of Education of China, School of Physics and Technology, Wuhan University, Wuhan
430072, PR China
b
Department of Chemistry, South University of Science and Technology of China, Shen Zhen, Guangdong 518000, PR China
ARTICLE INFO
Keywords:
Hole transport materials
Copper (II) phthalocyanine
Octamethyl-substituted
Molecular alignment
Long-term stability
ABSTRACT
Perovskite solar cells (PSCs) demonstrate huge potential in photovoltaic conversion, yet their practical
applications face one major obstacle: their instability. As to conventional hole transport materials (HTMs)
such as spiro-OMeTAD, their future commercialization maybe hampered for the cost and instability. Here, we
report a new HTM of copper (II) phthalocyanine with octamethyl-substituted function groups (CuMe
2
Pc).
Unlike the normal edge on orientation of pristine copper (II) phthalocyanine (CuPc), we found that CuMe
2
Pc
could form face-on molecular alignment when deposited on perovskite via vacuum thermal evaporation,
resulting in higher hole mobility, more condense thin film structure and more hydrophobic surface. These
properties are more favorable for hole transport and moisture resistance applications in PSCs. PSCs with planar
structure were fabricated and tested, utilizing different phthalocyanines and spiro-OMeTAD as HTMs. PSCs
with CuMe
2
Pc showed 25% higher power conversion efficiency (PCE) compared with those with CuPc.
Furthermore, beneficial from the hydrophobic nature of CuMe
2
Pc, the devices with CuMe
2
Pc as HTM show
improved stability and retained over 95% of their initial efficiencies even after storage in the humidity about
50% for 2000 h without encapsulation. This study demonstrates that CuMe
2
Pc is a potential HTM for
fabricating low-cost and efficient PSCs with long-term stability.
1. Introduction
In recent years, organic-inorganic lead halide perovskite solar cells
(PSCs) are attractive photovoltaic devices in view of their low cost, easy
fabrication, high efficiency [1–3]. Unfortunately, although highly
efficient perovskite solar cells have been demonstrated, some impor-
tant issues such as hysteresis, long-term stability and high cost of
synthesis of hole transport materials (HTMs) in perovskite solar cells
are still open problems and need to be concerned [4–7].
The most currently studied CH
3
NH
3
PbI
3
tends to degrade when it
was exposed to moisture, oxygen and heat stress, giving rise to reduced
device performance [8–13]. In view of this, many strategies have been
applied to make further progress in enhancing stability of perovskite
solar cells, such as perovskite materials engineered with hydrophobic
molecules, modifying perovskite with crosslinks neighbouring grain
surface, or adopting a polymer or metal oxide-scaffold structure and so
on [14–18]. Apart from these, improved contacts and interfaces,
including electron selective layer (ESL)/perovskite interface and per-
ovskite/hole selective layer (HSL) interface, demonstrate to be effective
approaches to enhance stability of PSCs [9,19–23]. Among these
approaches, perovskite/HSL interface engineering in conventional
PSCs is a simple method to protect perovskite from degradation from
moisture to some extent [11,22,24].
The most efficient PSCs have usually utilized HSL, which is responsible
for the hole extraction and simultaneously serves as an electron blocking
layer to retard charge recombination [25–27] .AnidealHSLforefficient
andstablePSCsshouldbedesirablycost-effective, high-mobility, highly
stable (against moisture and thermal stress). The most employed HTM in
efficient PSCs is 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-
spirobifluorene (spiro-OMeTAD), which inherently suffer from low hole
mobility (1×10
−5
to 1×10
−4
cm
2
/Vs) [28]. And p-doped spiro-OMeTAD
exhibitedenhancedmobilityafter adding lithium bis(trifl uoromethanesul-
http://dx.doi.org/10.1016/j.nanoen.2016.11.039
Received 18 September 2016; Received in revised form 14 October 2016; Accepted 20 November 2016
⁎
Corresponding authors.
1
Guang Yang, Yu-Long Wang and Jia-Ju Xu contributed equally.
E-mail addresses: xu.zx@sustc.edu.cn (Z.-X. Xu), gjfang@whu.edu.cn (G.-J. Fang).
Nano Energy 31 (2017) 322–330
Available online 21 November 2016
2211-2855/ © 2016 Elsevier Ltd. All rights reserved.
MARK