Controlled growth of Cu3Se2 nanosheets array counter electrode for quantum dots sensitized solar cell through ion exchange
Sci China Mater
Controlled growth of Cu3Se2 nanosheets array counter electrode for quantum dots sensitized solar cell through ion exchange
Huiwen Bai 1
Ting Shen 1
Shixun Wang 1
Bo Li 1
Guozhong Cao 0
Jianjun Tian 1
0 Department of Materials Science and Engineering, University of Washington , Seattle, WA 98195-2120 , USA
1 Institute of Advanced Materials and Technology, University of Science and Technology Beijing , Beijing 100083 , China
Copper selenide (CuxSe) has great potential as counter electrode for quantum dots sensitized solar cell (QDSSC) due to its excellent electrocatalytic activity and lower charge transfer resistance. A novel ion exchange method has been utilized to fabricate Cu3Se2 nanosheets array counter electrode. CdS layer was first deposited by sputtering and used as a template to grow compact and uniform Cu3Se2 film in a typical chemical bath. The morphology and thickness of the Cu3Se2 nanosheets were controlled by the deposition time. The final products (2h-Cu3Se2) showed significantly improved electrochemical catalytic activity and carrier transport property, leading to a much increased power conversion efficiency (4.01%) when compared with the CuS counter electrode CdS/CdSe QDSSC (3.21%).
Cu3Se2; counter electrode; quantum dots sensitized solar cell; ion exchange
INTRODUCTION
Quantum dots sensitized solar cells (QDSSCs), a promising
family of third-generation solar cells, possess significant
advantages on long-term photo-stability [1], large molar
extinction coefficients [2], easy tunable bandgap and the
potential multiple-exciton generation [3]. With the
aforementioned advantages, the theoretical maximum power
conversion efficiency (PCE) could reach 44%, exceeding
the Shockley-Queisser limit (33.4%) of single junction solar
cells [4]. Typically, QDSSC is assembled by a transparent
conductive substrate, a quantum dots loaded photoanode
film, polysulfide electrolyte and a counter electrode (CE)
[5]. As an important part of the photovoltaic device, CE
plays a critical role in the electrons transport and oxidation
of reduced ions [6], and thus is intensively investigated
in recent years. In principle, high electro-catalytic and
expected electrical conductivity activity are both required
for an excellent CE [7].
Three categories of materials are promising counter
electrode for QDSSCs, including noble metals [8], metal
sulfides [9–11], and porous carbon materials [12,13]. Pt has
been widely used in dye-sensitized solar cells owing to its
stability and high catalytic activity for the reduction of I3−
[14]. However, the cooperation of Pt and polysulfide
electrolyte in QDSSCs is less ideal, leading to a higher
overpotential and the inefficient interface catalytic activity [15].
Given that metal sulfides have excellent catalytic activity
when contacting with polysulfide electrolyte, the electrode
with such materials are reported to achieve the highest
conversion efficiency, such as CuS, CoS and PbS [16–20].
However, since CuS can react with polysulfide electrolyte,
contamination of the electrolyte and photoanode would affect
the PCE and the stability of the devices [21].
Copper selenide (CuxSe) shows great potential in
fabricating high efficiency CE for QDSSCs, due to its
excellent electrocatalytic activity and lower charge transfer
resistance [22,23]. Copper selenide is a family of
semiconductive metal chalcogenides with different stoichiometric
compositions and several crystal structures [24], such as
CuSe, CuSe2, Cu2Se, Cu3Se2. To synthesize copper selenides
with chemically stable crystal structures, several strategies
have been studied, including vacuum evaporation,
electrodeposition, successive ionic layer adsorption and
reaction (SILAR) and chemical bath deposition (CBD) [25,26].
Although many efforts have been made on this material,
the overall performance of solar cells are still unsatisfactory
[27].
Wang et al. [28] reported a hot-injection method for
synthesizing ultrathin Cu2−xSe nanosheet by cation exchange
(at 220–250°C). Besides, in our previous work [29], CuS
layer prepared by chemical deposition method was used
as seeds for the Cu3Se2 crystal nucleation. However, due
to the nonuniformity of CuS substrate prepared by SILAR
method, the substrate was not well covered by Cu3Se2
nanorods, which further limited the catalytic ability of the
CE. Here, CuxSe nanosheets array CE was synthesized via
a novel ion exchange strategy. By controlling the
processing time of chemical bath, the morphology of the CuxSe
nanosheets was accurately regulated. X-ray diffractometry
(XRD) and energy-dispersive X-ray spectroscopy (EDS)
were used to reveal the crystal structure and chemical
composition. When the CuxSe nanosheets array was used
as a CE in CdS/CdSe DQSSC, the PCE was significantly
improved as compared with CuS CE based solar cells,
owing to much increased catalytic activity, prolonged carriers’
lifetime and reduced interface recombination.
EXPERIMENTAL SECTION
Materials
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