纳米TiO_2颗粒/亚微米球多层结构薄膜内电荷传输性能研究

Characteristics of charge transport in nano-sized TiO_2 particles/submicron spheres multilayer thin-film electrode

本文主要利用Ti O2亚微米球较强的光散射特性设计了纳米Ti O2颗粒/亚微米球多层结构光阳极,并借助强度调制光电流谱(intensity-modulated photocurrent spectroscopy)、电化学阻抗谱(electrochemical impedance spectroscopy)和入射单色光光电转化效率(incident photon-to-current conversion efficiency),研究亚微米球的引入对多层结构薄膜内缺陷态、电子传输时间、电子收集效率和界面电荷转移性能的影响.强度调制光电流谱反映出亚微米球表面缺陷态少,但其颗粒间接触不紧密,导致在接触部位形成了势垒,阻碍了电子的传输,导致电子传输时间增长.电化学阻抗谱结果表明不同多层结构电池界面复合无明显差别,同时底层采用纳米Ti O2透明薄膜结构的电池,其光利用率要明显高于底层采用亚微米球薄膜结构的电池,Ti O2费米能级电子填充水平也相对增大,使得电池的光电转换效率得到提升.多层结构复合薄膜电荷传输和光伏特性的研究,为高效染料敏化太阳电池光阳极设计提供了实验基础.

In this work, we design the nano-sized TiO2 particles/submicron spheres multilayer structured photoanode, based on the fact of stronger light scattering properties of TiO2 submicron spheres. Effect of TiO2 submicron-spheres on the charge transport and interracial properties in multilayer thin-film electrodes are investigated in detail using intensity- modulated photocurrent spectroscopy （IMPS）, electrochemical impedance spectroscopy （EIS） and incident photon-to- current conversion efficiency （IPCE）. Results obtained from IMPS for dye-sensitized solar cells （DSCs） indicate that submicron-spheres have fewer defects, but the poor contact at the interfaces between submicron spheres hinders the electron transport and makes the transit time longer. EIS results show that there are no obvious differences in interface recombination between the designed electrodes. It is interesting to find that the bottom section of the photoanode composed of nano-sized TiO2 thin film has a higher light utilization efficiency than that composed of submicron-spheres; meanwhile, the Fermi level of TiO2 and the photovoltaic properties of DSCs have been extended. Our results may provide an experiment basis for structure design of high-efficiency DSC photoanode.