退火温度对TiO_2/CdSe纳米片异质结薄膜光电性能的影响

Effect of Annealing Temperature on Photoelectric Characteristics of TiO_2/CdSe Nanosheet Heterojunction Thin Films

采用水热法在FTO上制备(001)高活性晶面主导的TiO_2纳米片薄膜,利用循环伏安法在TiO_2纳米片薄膜上沉积CdSe颗粒,制备了TiO_2/CdSe纳米片异质结薄膜。分别在150、250、350、450℃,氩气保护气氛中对样品进行退火。利用X射线衍射仪(XRD)、场发射扫描电镜(FESEM)、X射线光电子能谱分析仪(XPS)、紫外-可见(UV-Vis)分光光度计以及电化学工作站对不同温度退火后的TiO_2/CdSe纳米片异质结薄膜的微观形貌、晶体结构、光电化学性能进行表征和测试。结果表明:六方相CdSe纳米颗粒均匀包覆在TiO_2纳米片表面,直径30 nm左右;随着退火温度的升高CdSe纳米颗粒长大,形成光滑的CdSe薄膜,且晶化程度提高;TiO_2纳米片表面的Se元素与Cd元素发生氧化;TiO_2/CdSe纳米片异质结薄膜对可见光的吸收光谱发生红移,禁带宽度逐渐减小。光电化学性能测试表明随着退火温度的升高,TiO_2/CdSe纳米片异质结薄膜的光电流密度显著提高,开路电压减小,但由于SeO_2和CdO的出现,导致填充因子减小,影响光电转换效率的提高。在本实验条件下,TiO_2/CdSe纳米片异质结薄膜的最佳退火温度为150℃,填充因子为0.77,光电转换效率达到3.12%。

TiO2 nanosheeet thin films were prepared by hydrothermal method. TiO2/CdSe nanosheet heterojunction thin films were prepared by electrochemical depositing CdSe nano-particles on the TiO2 nanosheets with （001） facets dominated. The synthesized films were annealed at 150, 250, 350 and 450℃ under the protection of Ar gas. The effect of annealing on TiO2/CdSe nanosheet heterojunction thin films was studied by X-ray diffraction（XRD）, field emission scanning eletron microscopy（FESEM）, X-ray photoelectron spectroscopy（XPS）, UV-Vis diffuse reflection spectrum（UV-Vis） and electrochemical workstation. The result indicates that hexagonal phase CdSe nanoparticles distribute on the surface of TiO2 nanosheet films uniformly with a diameter of 30 nm. With the increase of annealing temperature, CdSe nanoparticles are agglomerated and grown; the degree of crystallization increases; the Se and Cd on the surface of TiO2 nanosheets are oxidized; the absorption spectra appears red shift and the band gap reduces. The photoelectric performance test shows that the photocurrent density of the TiO2/CdSe nanosheet heterojunction thin films increases with the increase of the annealing temperature, but the open circuit voltage and the filling factor decreases, which leads to a reduction in the efficiency of photoelectric conversion. In this experimental condition, the optimum annealing temperature of TiO2/CdSe nanosheet heterojunction films is 150℃. The filling factor is 0.77 and the photoelectric conversion efficiency reaches 3.12%.