respectively. The samples were kept in the open air for a while
followed by gradual heating from 25–380 C on a hot plate for
15 min to burn off the PEG and to evaporate the solvents [21]. Later
on the sintering of the samples was done for 30 min at 450 C
(temperature rise and fall rate were 2 C/min) in order to get TiO2
compact films. The counter electrode was consisted of an ITO
coated with a graphite layer. As an electrolyte, Iodolyte HI-30 (from
Solaronix, Switzerland) was used.
To prepare the DSPS, 10 mg/ml concentrated solutions of MEHPPV
and PCPDTBT were prepared in chloroform and dichlorobenzene,
respectively. The dye sensitized electrodes were prepared by
dipping the TiO2 deposited ITO substrates in the different
volumetric ratio blends of MEH-PPV and PCPDTBT. The DSPS
devices were prepared using the dye-covered TiO2 electrodes
assembled with the graphite counter electrodes filled with the
redox electrolyte. The controlled sample for the PCPDTBT and
MEH-PPV were also fabricated, separately. Fig. 1(d) shows an
energy level diagram of the DSPS device, whereas Fig. 1(e)
describes the schematic diagram and working mechanism of the
DSPS. The liquid electrolyte (iodide/triiodide) in an organic solvent
as a redox system regenerate the oxidized organic dyes which
penetrate into the porous structure by collecting electrons through
the graphite counter electrode i.e., the positively charged organic
dye whereby I
3 ions are formed which diffuse to the cathode
(graphite). I
3 reduced to I
and hence the cycle is completed [22].
The photo excitation of the organic dyes leads to the injection of an
electron into the TiO2 conduction band. The electron passes
through the conductive oxide layer and the external load. The
optical absorption visible spectra have been recorded using
UV–vis–NIR spectrophotometer (A Lambda 750 UV/VIS/NIR
Spectrometer). The photoluminescence (PL) was studied by
employing a RENISHAW inVia Raman Microscope instrument,
with the 325 nm laser wavelength. The electrical characterization
of the electrochemical cells has been performed by computer
interfaced KEYSIGHT B2902A (precision source/measuring unit)
attached with an Oriel 67005 solar stimulator under different light
intensities (0–100 mW/cm2
). The light intensity was controlled
with the help of different range neutral density filters (NDL-25S-4).
The external quantum efficiency (EQE) was measured by using
the QEPVSI-b Quantum Efficiency Measurement System
(NEWPORT).