400
S. Datta and S. Roy
2.6 Characterization and Measurement
The optical properties of the films of KMnO 4 –TiO 2 were observed by UV–vis spectroscope (Hitachi Spectrophotometer U-4100, Japan). The surface morphologies of
the KMnO 4 –TiO 2 films were investigated by scanning electron microscope (Zeiss
EV 018, USA). The crystal structure of the KMnO 4 –TiO 2 films was characterized
using XRD (XPert PRO, USA) with a CuKα source (1.54 Å). Finally, all fabricated
cell’s electrical performance has been tested under simulated AM 1.5G solar illumination using 100 mW/cm
2 and this electrical measurement was done by a Keithley
2602A source meter (Keithley Instruments, USA).
3 Results and Discussion
SEM images of KMnO 4 –TiO 2 (2, 6, 10 wt%) thin films are shown in Fig. 2. Lower
particle size of TiO 2 with the addition of KMnO 4 leads to high adsorption of dye and
less scattering of lights. It was observed that the lower particle size of TiO 2 increases
the efficiency of the DSSC by forming suitable bandgap.
The chemical composition of the samples was investigated by EDS. EDS peaks
at 5.4 keV, 4.31 keV, and 0.43 keV represent the presence of Mn, Ti, and O elements,
respectively. The XRD pattern obtained for KMnO 4 –TiO 2 (2, 6, 10 wt%) films are
represented in Fig. 3. The strongest peaks 25.32°, 37.82°, 48.08° are corresponding
to the plane (101), (004), and (200) of TiO 2 . It was observed from the figure that
increase in the KMnO 4 percentage would decrease the d-spacing of the TiO 2 lattice
plane.
The optical bandgap of all the samples was calculated by using Tauc equation
from Fig. 4a (Hasan et al. 2010)
αhv = A
hv − E g
n
(1)
where E g is the optical energy gap, n = 1/2 for direct bandgap, which depends on the
nature of transition and hv is the photon energy (Mai et al. 2009). A graph between
(αhv)
n versus hv was plotted for bandgap calculation in Fig. 4b. It was observed that
TiO 2 pure, KMnO 4 –TiO 2 (2, 6, 10 wt%) film samples have approximately 3.6, 1.9,
1.7, and 1.45 eV.
Bandgap respectively which are the evidences of that the energy gap decreases
with the increasing of KMnO 4 percentage in the KMnO 4 –TiO 2 mixture. Figure 5a
represents the current density–voltage (J–V ) curve and (b) power–voltage curve of
KMnO 4 –TiO 2 (0, 2, 6, 10 wt%), which was tested under simulated AM 1.5G solar
illumination having light intensity of 100 mW/cm
2 . From the tabulated data, it was
found that the addition of KMnO 4 in the TiO 2 increases the photocurrent density as
well as the overall efficiency of the DSSC (Table 1).
S. Datta and S. Roy
2.6 Characterization and Measurement
The optical properties of the films of KMnO 4 –TiO 2 were observed by UV–vis spectroscope (Hitachi Spectrophotometer U-4100, Japan). The surface morphologies of
the KMnO 4 –TiO 2 films were investigated by scanning electron microscope (Zeiss
EV 018, USA). The crystal structure of the KMnO 4 –TiO 2 films was characterized
using XRD (XPert PRO, USA) with a CuKα source (1.54 Å). Finally, all fabricated
cell’s electrical performance has been tested under simulated AM 1.5G solar illumination using 100 mW/cm
2 and this electrical measurement was done by a Keithley
2602A source meter (Keithley Instruments, USA).
3 Results and Discussion
SEM images of KMnO 4 –TiO 2 (2, 6, 10 wt%) thin films are shown in Fig. 2. Lower
particle size of TiO 2 with the addition of KMnO 4 leads to high adsorption of dye and
less scattering of lights. It was observed that the lower particle size of TiO 2 increases
the efficiency of the DSSC by forming suitable bandgap.
The chemical composition of the samples was investigated by EDS. EDS peaks
at 5.4 keV, 4.31 keV, and 0.43 keV represent the presence of Mn, Ti, and O elements,
respectively. The XRD pattern obtained for KMnO 4 –TiO 2 (2, 6, 10 wt%) films are
represented in Fig. 3. The strongest peaks 25.32°, 37.82°, 48.08° are corresponding
to the plane (101), (004), and (200) of TiO 2 . It was observed from the figure that
increase in the KMnO 4 percentage would decrease the d-spacing of the TiO 2 lattice
plane.
The optical bandgap of all the samples was calculated by using Tauc equation
from Fig. 4a (Hasan et al. 2010)
αhv = A
hv − E g
n
(1)
where E g is the optical energy gap, n = 1/2 for direct bandgap, which depends on the
nature of transition and hv is the photon energy (Mai et al. 2009). A graph between
(αhv)
n versus hv was plotted for bandgap calculation in Fig. 4b. It was observed that
TiO 2 pure, KMnO 4 –TiO 2 (2, 6, 10 wt%) film samples have approximately 3.6, 1.9,
1.7, and 1.45 eV.
Bandgap respectively which are the evidences of that the energy gap decreases
with the increasing of KMnO 4 percentage in the KMnO 4 –TiO 2 mixture. Figure 5a
represents the current density–voltage (J–V ) curve and (b) power–voltage curve of
KMnO 4 –TiO 2 (0, 2, 6, 10 wt%), which was tested under simulated AM 1.5G solar
illumination having light intensity of 100 mW/cm
2 . From the tabulated data, it was
found that the addition of KMnO 4 in the TiO 2 increases the photocurrent density as
well as the overall efficiency of the DSSC (Table 1).