Abstract:
Photocurrent quantum efficiency of liquid photovoltaic cells (PECs) is largely limited
by the rapid recombination of the photogenerated charge carriers at the solid defect
as well as at the interface. In solid state photovoltaics, the problem is more serious
with polycrystalline materials because of the rapid recombination of carriers before
separation by the barrier field. In liquid photovoltaics, the minority carriers tunnelling
into the medium are transferred more efficiently when charge transfer agents are
present. Therefore this study was undertaken to look for the possibilities to enhancing
the photocurrent quantum efficiency in PECs by suppression of recombination or
other losses.
It is observed that when the p-type Cu20 is coated with the cationic forms of different
dyes(whereas the anionic ligand of the dye is salicylate ion), photocurrent generation
in the bandgap region wavelength is also enhanced. The effect is explained as
originating from the suppression of the recombination of the carriers generated by the
photons captured directly by the semiconductor surface.
Deposition of thin films of polynuclear metal cyanide films of Prussian Blue(PB) on
CdS photoelectrodes is found to increase the photocurrent in CdS. The efficient hole
trapping in PB and an effective removal of holes from PB by adsorbed redox species
suppress recombinations.
Photoelectrochemical cell based on microporous cuprous iodide(CuI) photoelectrode
sensitized with natural pigment chlorophyll was studied. Characteristics of the photocurrent spectra of the chlorophyll sensitized microporous cuprous iodide film
under back wall mode and front wall mode illumination give evidences to the
existence of diffusion controlled charge transfer process between colloidal particles
of cuprous iodide.
It is observed that the treatment of microporous Ti02 film with tannins and related
polyphenolic substances produces Ti4+-tannin or Ti4+-phenol charge transfer
complexes firmly affixed to the surface of Ti02 crystallites. Efficient
photosensitization originating from the surface chelated charge transfer complex
generates high photocurrents in liquid photovoltaic cells.
