Trapping detrapping

K. L. Wilson, et al.. Trapping, Detrapping and Release of Implanted Hydrogen Isotopes, 1991, IAEA. 

Some mechanisms could mitigate charge recombination in Gratzel-type cells a dye bonded to the Ti02 surface passivates recombination centers, and suppression of trapping-detrapping events at the surface... 

Bixon M, Jortner J (2001) Hole trapping, detrapping and hopping in DNA. J Phys Chem A 105 10322-10328... 

The above observations have been interpreted within the framework of two distinct models, one involving trapping/detrapping of the photogenerated electrons [345, 346] and the other based on electron diffusion (or field-assisted diffusion) not attenuated by electron localization [347, 348]. The millisecond transit times also mean that the transit times are very long compared with equilibration of majority carriers in a bulk semiconductor or electron-hole pair separation within the depletion layer of a flat electrode. The slow transport is rationalized by a weak driving force and by invoking percolation effects [338]. 

Another model based on the same experimental results has been proposed [148]. Traps with a distribution of the potential depth are preformed in the matrix. The electrons generated at 4°K are stabilized in the shallower traps. Detrapping and subsequent retrapping in the deeper traps occur during warming from 4 to 77° K. 

Fig. 20 Energy scheme for photogeneration and diffusion of electrons in a porous photoelectrode under steady state conditions. The light -hv is incident from the electrolyte side (x = 0) and is absorbed in a region of width 1 /a. Photogenerated electrons diffuse toward the collecting back contact (x = d) caused by a gradient in the electrochemical potential Ep (dashed line). Transport is attenuated by multiple trapping/detrapping.

Including trapping/detrapping in the model that leads to the transfer function expressed by Eq. (37) does not alter the optoelectrical transfer function itself. However, the transit time that is obtained from (Dm is increased by a factor [1 + S( F n)]- The value of the trapping parameter E( f ) (with respect to 1)... 

Equation (12) is all the information we need to modify the cmituiuity equatimis to take trapping, detrapping and recombination via traps into account. However, what is still missing is the influence of the trap levels on the space charge and subsequently the Poissmi equation. 

The decay of a small population that serves as a probe of the kinetics of the system has therefore been characterized for any recombination rate law and steady state condition. More generally, the decay may require a number of sequential processes coupled to recombination, for example when prior detrapping of localized carriers is required, as we discuss later on. The free carrier lifetime Tf in (61) does not yet consider the trapping-detrapping dynamics, but just the charge... 

Figure 3.22 (a) The main processes determining the collection efficiency of electron transport in DSSCs. (b) Schematic drawing of the trapping/detrapping process. Electrons in trap states are thermally excited to the conduction band (CB) where they are mobile and can undergo transport towards the conducting substrate or recombination to the electrolyte or oxidised dyes... 

Transport to the Surface, Trapping, Detrapping, and Recombination of Charges... 

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