A Research On Wet Etching And Photothermal Properties Of Layered Selenium Compounds Materials

Selenide layered materials are most extensively studied semiconducting compound because of their properties that make them attractive for applications in in the field of thin film solar cells and thermoelectric devices. In this paper, we have studied the properties, preparation methods and application of Bi2Se3(V-VI) and In2Se3(III-VI), respectively. Single crystalline Bi2Se3 thin films grown on(111)-oriented Si substrates by physical vapor deposition(PVD) are employed in this study. The single crystalline α-phase In2Se3 thin films were achieved on Si(111) substrate by molecular beam epitaxy(MBE). We have researched the etching properties of Bi2Se3 and the optical electrical properties of In2Se3 to explore the characteristics of the selenium compound layer material. The experimental results are as follows:(1) We studied the etching effect and reaction mechanism of two different etching liquid for patterning single crystalline Bi2Se3 thin film. Acidic potassium dichromate solutions(K2Cr2O7-H2SO4 and K2Cr2O7-HCl) are applied for patterning Bi2Se3 thin films on Si(111) substrates. Mesa-shaped etching profile of Bi2Se3 is obtained either in K2Cr2O7-HCl or K2Cr2O7-H2SO4 aqueous solutions with H+ concentrations of 8 mol/L and 12 mol/L, respectively. The dissolving rates of Bi2Se3 are both approximately 120 nm/min. Though either etchant is qualified for patterning Bi2Se3, the reaction products on surfaces of the etched samples are different. After being immersed in K2Cr2O7-H2SO4 solution for 30 seconds which corresponds to an etching depth of ~ 60 nm, these pyramid morphologies completely vanish and a surface decorated with large circular islands sized from ~ 20 nm to ~ 300 nm. A much smoother surface is obtained for Bi2Se3 in K2Cr2O7-HCl solution and the surface is full depletion of Se. As we know slightly metal-rich surface may benefit a low-resistance ohmic contact formation between Bi2Se3 and electrode metals of devices. Our findings may serve as useful reference for fabricating Bi2Se3-based devices with various purposes.(2) We studied the electronic and optical properties of the solar cell based on α-In2Se3 thin film grown on Si(111). Current-voltage-temperature(I-V-T) measurements and conversion efficiency were performed. By control the substrate temperature during growth, we achieved single crystalline α phase In2Se3 thin film by molecular beam epitaxy. Structural and surface morphology details of the as-grown films were characterized by X-ray diffraction and scanning electron microscopy, respectively. We manufactured the sample into an efficient solar cell and the external quantum efficiency(EQE) test was performed. Although the device has not been treated, the sample showed an EQE over 20% in the range of 540 nm to 860 nm, and the photoresponse extended to 880 nm. When tested in atmosphere ambient under simulated 1-sun(100 mW cm-2) test conditions, the short-circuit photocurrent density(JSC), open-circuit voltage(VOC) and fill factor(ff) of In2Se3 film device, fabricated without anti-reflecting coating and normalized to the area of 0.2 cm2, were JSC = 9.6 mA cm-2, VOC = 247 mV and ff = 32.3%, respectively, corresponding to a total area conversion efficiency of 0.77%. The result show that theα-In2Se3 film fabricated by MBE can be achieve a high photoelectric conversion efficiency, which could be potential candidate for future transport and optical studies. In2Se3 thin film has enormous development potential for applications in electrochemical and photovoltaic devices.