Intensity dependence of the back reaction and transport of electrons in dye-sensitized nanocrystalline TiO{sub 2} solar cells
The lifetime {tau}{sub n} and diffusion coefficient D{sub n} of photoinjected electrons have been measured in a dye-sensitized nanocrystalline TiO{sub 2} solar cell over 5 orders of magnitude of illumination intensity using intensity-modulated photovoltage and photocurrent spectroscopies. {tau}{sub n} was found to be inversely proportional to the square root of the steady-state light intensity, I{sub 0}, whereas D{sub n} varied with I{sub 0}{sup 0.68}. The intensity dependence of {tau}{sub n} is interpreted as evidence that the back reaction of electrons with I{sub 3}{sup {minus}} may be second order in electron density. The intensity dependence of D{sub n} is attributed to an exponential trap density distribution of the form N{sub t}(E) {proportional{underscore}to} exp[{minus}{beta}(E - E{sub c})/(K{sub B}T)] with {beta} {approximately} 0.6. since {tau}{sub n} and D{sub n} vary with intensity in opposite senses, the calculated electron diffusion length L{sub n} = (D{sub n}{tau}{sub n}){sup 1/2} falls by less than a factor of 5 when the intensity is reduced by 5 orders of magnitude. The incident photon to current efficiency (IPCE) is predicted to decrease by less than 10% over the same range of illumination intensity, and the experimental results confirm this prediction.
- Research Organization:
- Univ. of Bath (GB)
- OSTI ID:
- 20017304
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 104, Issue 5; Other Information: PBD: 10 Feb 2000; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- English
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