Temperature dependence of the electron diffusion coefficient in electrolyte-filledTiO2nanoparticle films: Evidence against multiple trapping in exponential conduction-band tails

Abstract

The temperature and photoexcitation density dependences of the electron transport dynamics in electrolytefilled mesoporous TiO 2 nanoparticle films were investigated by transient photocurrent measurements. The thermal activation energy of the diffusion coefficient of photogenerated electrons ranged from 0.19-0.27 eV, depending on the specific sample studied. The diffusion coefficient also depends strongly on the photoexcitation density; however, the activation energy has little, if any, dependence on the photoexcitation density. The light intensity dependence can be used to infer temperature-independent dispersion parameters in the range 0.3-0.5. These results are inconsistent with the widely used transport model that assumes multiple trapping of electrons in an exponential conduction-band tail. We can also exclude a model allowing for widening of a band tail with increased temperature. Our results suggest that structural, not energetic, disorder limits electron transport in mesoporous TiO 2 . The analogy between this material and others in which charge transport is limited by structural disorder is discussed.

Structural, optical and charge transport study of rutile TiO2 nanocrystals at two calcination temperatures

“…The more traps are filled, the easier for an electron to escape from these traps and the quicker the saturation in PC can be achieved. For TiO 2 nanocrystals average trap-depths between 0.10 and 0.27 eV have been proposed in literature [65,66]. In our case trap depth or trap ionization energies for samples R1 comes out as 0.65 eV and for sample R2 as 0.69 eV, which is much greater than the reported value of trap depth for pure TiO 2 .…”

Electron trapping induced electrostatic adsorption of cations: a general factor leading to photoactivity decay of nanostructured TiO2

“…[38][39][40] The other is that the detrapping energy barrier may be increased due to the electrostatic attraction between trapped electrons and protons as well as other cations. For nanostructured TiO 2 , the interface transfer of holes is at nanosecond regime while electron transport in TiO 2 is markedly slow, 41 which certainly will cause electron trapping and consequent ETPU. Therefore, along with the proceeding of PEC process the continuous occurrence of ETPU leads to continually increase of transport resistance shown in Figure s7c, which we believe is the essential cause for the general and continuous photoactivity decay typically shown in Figure 1.…”

Compact Inverse‐Opal Electrode Using Non‐Aggregated TiO2 Nanoparticles for Dye‐Sensitized Solar Cells

“…In addition, the disordered geometrical structures in nanoparticle-based DSSCs are limiting factors for achieving higher efficiency due to interfacial interference for electron transport. [5][6][7][8][9][10][11][12] The trap-limited diffusion process in randomly connected networks can be disturbed by recombination with the oxidizing species in the electrolyte during a number of trapping steps. [3,13,14] In conjunction with these efforts, recent studies on photoelectrodes have expanded the processing strategies by using periodic nanostructures with long-range ordering to better assure an interconnected morphology of the TiO 2 structure.…”