Synthesis of Wurtzite Cu2ZnSnS4 Nanosheets with Exposed High-Energy (002) Facets for Fabrication of Efficient Pt-Free Solar Cell Counter Electrodes

Xiaoyan Zhang,Ningzhong Bao,Shuai Dong,Arunava Gupta,Junjie Zhang,You Xu,Liming Shen

doi:10.1038/s41598-017-18631-0

Abstract

Two-dimensional (2D) semiconducting nanomaterials have generated much interest both because of fundamental scientific interest and technological applications arising from the unique properties in two dimensions. However, the colloidal synthesis of 2D quaternary chalcogenide nanomaterials remains a great challenge owing to the lack of intrinsic driving force for its anisotropic growth. 2D wurtzite Cu2ZnSnS4 nanosheets (CZTS-NS) with high-energy (002) facets have been obtained for the first time via a simple one-pot thermal decomposition method. The CZTS-NS exhibits superior photoelectrochemical activity as compared to zero-dimensional CZTS nanospheres and comparable performance to Pt counter electrode for dye sensitized solar cells. The improved catalytic activity can be attributed to additional reactive catalytic sites and higher catalytic reactivity in high-energy (002) facets of 2D CZTS-NS. This is in accordance with the density functional theory (DFT) calculations, which indicates that the (002) facets of wurtzite CZTS-NS possess higher surface energy and exhibits remarkable reducibility for I3− ions. The developed synthetic method and findings will be helpful for the design and synthesis of 2D semiconducting nanomaterials, especially eco-friendly copper chalcogenide nanocrystals for energy harvesting and photoelectric applications.

Highlights

With recent great progress of both traditional and emerging 3rd generation solar cells, photovoltaics provide one of lowest-cost options for future electricity generation[1,2]
The successful synthesis of wurtzite 2D CZTS nanosheets (CZTS-NS) takes advantage of using excess 1-DDT as both the sulfur source and reaction solvent. 1-DDT has been widely used as a sulfur source that can balance the reactivity of cations in the solution and passivate the obtained wurtzite nanocrystals[28,41,42,44]
Since no standard X-ray diffraction (XRD) pattern for wurtzite CZTS exists in the database, a simulated pattern has been obtained based on the structure[28]

Summary

Introduction

With recent great progress of both traditional (silicon, thin film solar cells, etc.) and emerging 3rd generation solar cells (dye-sensitized, quantum dot, and perovskite solar cells, etc.), photovoltaics provide one of lowest-cost options for future electricity generation[1,2]. According to crystal growth theory, high energy crystal facets tend to disappear rapidly during the crystal growth process, as the growth rate perpendicular to a high-energy facet is much faster than that along the normal direction of a low-energy facet[29,30,31] Various methods, such as solvothermal, pulsed laser deposition, and spray pyrolysis have been used to form CZTS nanosheets/ nanoplate arrays on substrates[21,22,32,33,34], while the complicated synthesis procedure and the vacuum based process hinder their wide applications. Based on our previous work, we have built up the method to synthesize a series of ternary and quaternary chalcogenide nanocrystals with controlled crystal phase (wurtzite, zinc blend, and kesterite)[28,41,42], and morphology (rods, rice-like, bullets, etc.). The efficient and scalable method for preparation of 2D nanomaterials paves a new way for synthsis other copper-based chalcogenide nanomaterials, which shows potential for energy harvesting and photoelectric applications

Methods

Results

Discussion

Conclusion