Surface-treated Cu 2 ZnSnS 4 nanoflakes as Pt-free inexpensive and effective counter electrode in DSSC
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Surface-treated Cu2ZnSnS4 nanoflakes as Pt-free inexpensive and effective counter electrode in DSSC C. Imla Mary1, M. Senthilkumar1, G. Manobalaji1, and S. Moorthy Babu1,* 1
Crystal Growth Centre, Anna University, Chennai 600 025, India
Received: 7 June 2020
ABSTRACT
Accepted: 27 August 2020
Inexpensive semiconducting counter electrode (CE) was fabricated from copper zinc tin sulfide (CZTS) nanoflakes (NFs) through simple non-vacuum-based techniques. The kesterite CZTS NFs were synthesized by hot injection method using oleic acid as solvent. CZTS CE was prepared through solid-state ligand exchange method using ammonium sulfide salt ((NH4)2S) as the displacement ligand. Thin-film CZTS CE (on FTO substrate) was developed through inexpensive layer-by-layer (LbL) approach, without any post-treatment such as toxic sulfurization process. Hence, the fabrication of CZTS CE through this approach is scalable. The CZTS thin film showed NFs like morphology with higher surface area and achieved good electrocatalytic activity towards the reduction of iodide electrolyte. Two DSSCs using different CEs (CZTS NFs and Pt) were fabricated in separate cell structures in our laboratory. DSSC with CZTS NFs as CE showed the power conversion efficiency of 2.95% which is comparable to the DSSC with Pt (3.11%).
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
1 Introduction The efficient utilization of renewable energy is the most compelling and essential research field to address the issues of global warming and increasing energy crisis all over the world [1]. Thin-film solar cells including dye-sensitized solar cells (DSSCs) have gained more attention due to the low-cost preparation techniques, high-throughput manufacturing methods, environmental friendliness and promising power conversion efficiency (g [ 15%) [2, 3]. DSSCs consist of three major parts, i.e., photoanode, redox electrolyte (I3-/I-) and counter electrode (CE) [3]. In general, platinum (Pt)-coated
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https://doi.org/10.1007/s10854-020-04365-9
fluorine-doped tin oxide (FTO) glass substrates are used as a conventional CE in commercial DSSCs. Nonetheless, the usage of Pt is problematic for largescale application due to the high cost and lack of abundance in nature [3, 4]. Additionally, the longterm exposure of Pt CE onto the iodide electrolyte leads to the decomposition of Pt into unwanted PtI4 and H2PtI6, which affects the long-term stability of DSSC [4, 5]. The surge of Pt-free inexpensive CE is the most compelling research problem in emerging DSSCs. The Pt CE has been replaced using various alternative materials such as carbonaceous materials, conducting polymers and inorganic compounds [6–10]. Among these materials, the inorganic
J Mater Sci: Mater Electron
semiconducting compounds such as copper zinc tin sulfide (CZTS) received much attention as promising CE in DSSCs. The constituent elements of CZTS are earth abundant and inexpensive. It is a p-type direct bandgap material (1.5 eV) and
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