V-VI, I-III-VI2, I2-II-IV-VI4硫族化合物半導體材料電化學合成

Abstract

Electrochemistry studies the electrons transfer of the chemical moieties in the electrolytic solution, thus, inert materials which only supply or withdraw electrons such as pyrolytic graphite and platinum are commonly used as the electrodes in the electroanalyses. However, in most of the cases, the materials we utilized for the working electrode are not as nonreactive as pyrolytic graphite or platinum, and will take place the chemical reactions during supplying or withdrawing electrons. We focused on investigating the chemical reaction between the chemical moieties in electrolytic solution and the working electrode materials including V-VI semiconductor of Bi2Te3, I-III-VI2 semiconductor of Cu(In,Ga)Se2, and I2-II-IV-VI4 semiconductor of Cu2ZnSnS4 and hence developed four kinds of techniques, as mentioned as follows: (i) We demonstrate an one-step electrolysis process to directly form Bi2Te3 nanosheet arrays (NSAs) on the surface of Bi2Te3 bulk with controllable spacing distance and depth by tuning the applied bias and duration. The single sheet of NSAs reveals that the average thickness and electrical resistivity of single crystalline Bi2Te3 in composition are 399.8 nm and 137.34 μΩ⋅m, respectively. The formation mechanism and the selection rules of NSAs have been proposed. A 1.12 % energy conversion efficiency of quantum-dot-sensitized solar cells with Bi2Te3 NSAs as counter electrode has been demonstrated. (ii) We propose a gas-solid transformation mechanism to synthesize surfactant-free tellurium nanowires with average diameter under 20 nm at room temperature by one-step electrochemical method. The tellurium nanowires grow along the [001] direction due to the unique spiral chains in crystal structure and show an enhanced Raman scattering effect, a broad absorption band over the range of 350-750 nm and an emission band over the range of 400-700 nm in photoluminescence spectrum. Besides, the tellurium nanowires are directly applied as p-type dopant to dope graphene and result in a right shift of Dirac point in graphene field-effect transistor. Finally, we apply these tellurium nanowires as a supercapacitor electrode and demonstrate their promising capacitive properties. (iii) We introduce a surface modification on CIGSe thin film by electrochemical treatment. After this electrochemical passivation treatment, a lower oxygen concentration near the CIGSe surface was detected by XPS analysis. Temperature-dependent J-V characteristics of CIGSe solar cells reveal that the interface recombination can be suppressed and an improved rollover condition can be achieved. As a result, the defects near the CIGSe surface can be passivated by electrolysis and the performance of CIGSe solar cells can be enhanced from 4.7 % to 7.7 %. (iv) We demonstrate a one-step hybrid electrodeposition method which combines electrophoretic and electroplated electrodeposition to synthesize CZTS thin film. To our best condition, the composition of the as-deposited CZTS thin film can be achieved to be ~25.33 at%, ~19.44 at%, ~14.56 at%, and ~40.67 at% for Cu, Zn, Sn, and S elements, respectively. After the 550°C sulfurization for 1 hour in a sulfur vapor atmosphere, three diffraction peaks corresponding to the (112), (220), and (312) planes of CZTS could be detected in XRD spectra. The A Raman-active vibration modes at 287, 338 cm-1 and B Raman-active vibration modes at 374 cm-1 could be identified as kesterite CZTS in Raman spectra. An appropriate optical property of 1.48 eV band gap is achieved for photovoltaic application. Through careful analysis and optimization, we are able to demonstrate CZTS solar cells with the VOC, JSC, FF and η of 350 mV, 3.90 mA/cm2, 0.43 and 0.59 %, respectively.