Controllable Preparation,Formation Mechanism And Photoelectric Properties Of Chalcogenide Semiconductor Nanomaterials

Since the21st century, the world’s demand for solar cells are growing at a rate of40%each year. More attention is focused on developing renewable energy. As a core component of the solar cell, absorption layer has many kinds of materials. However, applications of some existing materials are developed slowly due to the unfavorable features of low performance, high costs and environmental incompatibility. Chalcogenide semiconductor nano-materials have aroused great interest thanks to its speacial optical properties, electrical properties, photoelectric conversion characteristics and catalytic properties. Recently, most investigations are concentrated on II-VI (CdS, HgSe), Ⅳ-Ⅵ(PbS, PbSe) and multi-sulfide semiconductor nano-materials such as CuxS1-x, CIGS (CuInGaSe2), CZTS (Cu2ZnSnS4). Some materials are limited by following factors:poisonous components (Cd、Hg); high cost of raw materials (In and Ga); low conversion efficiency. Some compounds consisted of S, Cu, Zn, Ge elements have potential applications in solar absorption materials and are suitable for large-scale, low-cost solar cells production. Therefore, we synthesized GeS、 GeSe and CZTS nanocrystalline materials and studied their applications in solar absorption materials. A series of works have been conducted as follows:1. We introduced a flexible solvent method to selectively synthesis GeSe single crystal nanostructures (nanobelts and nanosheets) controlled by changing the solvent and the content of precursors. A large excess of reactant Se in the reaction could promote the anisotropic growth and produced the GeSe nanobelts. The phases and components of the products were determined by X-ray Diffraction (XRD) and Energy Dispersive X-ray spectroscopy (EDX). Their morphology, micro-structures and the growth direction were also characterized and analyzed by scanning electronmicroscope (SEM), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM). At last, we discussed mechanism and conditions of the products during the process.2. GeS nanostructures have been prepared in a controllable manner via a convenient wet-chemical approach. Single crystalline nanosheets and nanowires of GeS can be selectively synthesized by simply varying reaction conditions. During the reaction process, OLA acted as both an activation agent and an effective capping ligand. Time-dependent reactions results proved that the GeS nanowires are formed by the rolling-up mechanism. The driving force of rolling-up may originate from the surface tension induced by the interaction of the GeS nanosheets with OLA molecules. The structure, morphology, composition and optical absorption properties of the as-prepared samples were characterized using X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectrometry, scanning electron microscopy and UV-Vis spectrophotometer.3. An one-step hydrothermal process for fabrication of CZTS nanosheets has been developed. The as-prepared CZTS nanosheets have an average thickness of10nm and show a high absorbance in the visible region with a direct band gap of1.48eV. A possible PVP-assistance formation mechanism of CZTS nanosheets has been proposed. The present convenient and low-cost preparation approach makes it highly attractive for practical applications.