Controlled growth of Cu3Se2 nanosheets array counter electrode for quantum dots sensitized solar cell through ion exchange

Science China Materials, May 2017

Copper selenide (Cu x Se) 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%).

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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 Cupric a (...truncated)


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Huiwen Bai, Ting Shen, Shixun Wang, Bo Li, Guozhong Cao, Jianjun Tian. Controlled growth of Cu3Se2 nanosheets array counter electrode for quantum dots sensitized solar cell through ion exchange, Science China Materials, 2017, pp. 637-645, Volume 60, Issue 7, DOI: 10.1007/s40843-017-9037-1