纳米TiO2的光生电荷迁移特性研究

利用场诱导光电压谱(简称FISPS)和瞬态光伏(简称TPV)技术研究了TiO₂的光生电荷的产生和传输机制.发现光生电荷在体块TiO₂上的迁移机制不同于在纳米TiO₂上的迁移机制，也不同于在结界面空间电荷区的迁移机制. 400 ℃处理的TiO₂颗粒表面具有大量的表面态，光生电荷被表面态捕获-释放机制控制着光伏行为的过程是慢过程. 800 ℃处理的TiO₂已经形成了完整的能带结构，光伏响应除了表现带-带跃迁外,还有一个在带边的自由激子带，光生电荷被表面自建场驱动进行传递的过程是快过程. 600 ℃处理的TiO₂混晶由锐钛矿型和金红石型两种构型组成，在两相之间存在着较低势垒的结界面．它的光伏响应受控于两种机制 ：光生电荷在两相间结界面空间电荷区的传输和在表面自建场驱动下的传输.当激发光强较小时，界面空间电荷区的光生电子由于积累的浓度较小而不能隧穿过结界面，这种场助隧穿只有在外场作用下才能发生.

Research on Characteristics of Photogenerated Charge in Nano-TiO2

The photo-generated carriers properties of TiO₂ nanoparticles annealed at different temperatures have been studied by the field induced surface photovoltage spectroscopy(FISPS) and transient photovoltage (TPV)technique. The transport mechanism of photogenerated electron in bulk phase is different from that in nano-TiO₂ and space charge region of interface of junction. Due to sufficient surface states of TiO₂ annealed under 400 ℃, photovoltage is controlled by the mechanism that photogenerated charge is captured and decaptured by surface states, which is attributed to slow process. After annealed at 800 ℃, the bigger particle is obtained and the energy band has been formed completely. Consequently, except for band-band transition, a band relates to free exciton transition appeared in the band edge in FISPS. The photovoltage is consistent with the direction of external field. The photovoltage is driven by surface built-in field of particles, which is a quick process. While, the powder annealed at 600 ℃, the surface phtovoltage presents the characteristics of homojunction for different crystalline interface. So the low potential barrier presents at interface of anatase phase and rutile phase. The photovoltage is driven by surface built-in field and space charge region of interface of two phases. The photogenerated electron cannot tunnel the interface when it is illuminated by weak light, unless an external electric field is applied.