Powder X-ray Diffraction Analysis
Figure 1.1 shows the powder X-ray diffraction (PXRD) spectra of benzoguanamine (0%, 10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films. The benzoguanamine (0%, 10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films exhibited X-ray diffraction peaks at 2θ = 20o, 22o, 25o, 36o, 42o and 44o. The peak’s intensity of 0% benzoguanamine doped PVDF/KI/I2 electrolyte film is higher than the benzoguanamine (10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films. These results confirmed the decreased crystallinity of benzoguanamine (10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films. When the benzoguanamine is added, the intensity of peaks was found to be gradually decreased up to 20%. This confirmed the decreased crystallinity of benzoguanamine (10% and 20%) doped PVDF/KI/I2 electrolyte films. But when the amount of benzoguanamine was increased further, the intensity of peaks was gradually increased. This confirmed the increased crystallinity of benzoguanamine (30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films. The results obtained from the PXRD measurements confirm the lowest crystallinity of 20% benzoguanamine doped PVDF/KI/I2 electrolyte film than the other benzoguanamine (0%, 10%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films.
Ionic Conductivity Studies
The AC-impedance spectra of prepared benzoguanamine (0%, 10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films are presented in Fig. 1.2. The ionic conductivity of benzoguanamine doped PVDF/KI/I2 electrolyte films was measured from Fig. 1.2, and the obtained values are listed in Table 1.1. The ionic conductivity of benzoguanamine (0%, 10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films are 5.57 × 10− 6 Scm− 1, 1.05 × 10− 5 Scm− 1, 5.95 × 10− 5 Scm− 1, 3.09 × 10− 5 Scm− 1, 1.56 × 10− 5 Scm− 1 and 1.48 × 10− 5 Scm− 1, respectively. The benzoguanamine (10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films have higher ionic conductivity than the 0% benzoguanamine doped PVDF/KI/I2 electrolyte film. The reason for the observed trend is the addition of benzoguanamine. The ionic conductivity was increased with the addition of benzoguanamine up to 20%. This may be due to the increased number of mobile charge carriers and chain mobility of polymer electrolytes [11, 12]. After 20%, the ionic conductivity of benzoguanamine (30%, 40% and 50%) doped electrolyte films was found to be decreased. This is due to the taking up of some free volume, the rapid increase in viscosity and some benzoguanamine may not be dissociated in polymer electrolytes. So, it causes the interrupted mobility of the charge carriers and thereby reduces the ionic conductivity [11]. The highest ionic conductivity was obtained for 20% benzoguanamine doped PVDF/KI/I2 electrolyte film. This highest ionic conductivity is responsible for the highest power conversion efficiency of DSSC. Figure 1.3 represents the plot of ionic conductivity variations of benzoguanamine doped PVDF/KI/I2 electrolyte films.
Table 1.1
Conductivity of benzoguanamine (a) 0%, (b) 10%, (c) 20%, (d) 30%, (e) 40% and (f) 50% doped PVDF/KI/I2 electrolyte films
Electrolyte
|
Benzoguanamine (%)
|
Ionic Conductivity (Scm− 1)
|
a
|
0
|
5.57 × 10− 6
|
b
|
10
|
1.05 × 10− 5
|
c
|
20
|
5.95 × 10− 5
|
d
|
30
|
3.09 × 10− 5
|
e
|
40
|
1.56 × 10− 5
|
f
|
50
|
1.48 × 10− 5
|
Scanning Electron Microscopy Analysis
The surface morphology of benzoguanamine (0%, 10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films is characterized by scanning electron microscopy (SEM) analysis. The SEM images of benzoguanamine (0%, 10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films are presented in Fig. 1.4. The surface morphology of benzoguanamine doped PVDF/KI/I2 electrolyte films has shown the spherical particles with voids. The 0% benzoguanamine doped PVDF/KI/I2 electrolyte film has the largest size spherical particles voids than the benzoguanamine (10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolyte films. The spherical particle size was gradually decreased with voids up to 20% of benzoguanamine doped PVDF/KI/I2 electrolyte films. In the 30%, 40% and 50% of benzoguanamine doped PVDF/KI/I2 electrolyte films, the spherical particle size was gradually increased with voids. The 20% benzoguanamine doped PVDF/KI/I2 electrolyte film has shown the smallest spherical particles with voids. The benzoguanamine contributes a notable effect in the benzoguanamine doped PVDF/KI/I2 electrolyte films [13, 14].
Photovoltaic Measurements
The DSSCs were fabricated with the prepared benzoguanamine (0%, 10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolytes. The current density-voltage (J-V) curves of DSSCs with the benzoguanamine (0%, 10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolytes are presented in Fig. 1.5. The photovoltaic parameters of DSSCs with benzoguanamine (0%, 10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolytes are exhibited as Jsc=5.50 mA/cm2, Voc=0.72 V, FF = 0.38 and η = 1.5%; Jsc=6.28 mA/cm2, Voc=0.71 V, FF = 0.43 and η = 1.9%; Jsc=8.34 mA/cm2, Voc=0.69 V, FF = 0.49 and η = 2.8%; Jsc=7.95 mA/cm2, Voc=0.70 V, FF = 0.46 and η = 2.5%; Jsc=7.48 mA/cm2, Voc=0.73 V, FF = 0.42 and η = 2.3%; Jsc=6.86 mA/cm2, Voc=0.72 V, FF = 0.42 and η = 2.1%, respectively. The calculated photovoltaic parameters of DSSCs are summarized in Table 1.2. The DSSCs with the benzoguanamine (10%, 20%, 30%, 40% and 50%) doped PVDF/KI/I2 electrolytes have higher power conversion efficiency than the DSSC with the 0% benzoguanamine doped PVDF/KI/I2 electrolyte. This is due to the electron donating capability of benzoguanamine. It has nitrogen atoms in its structure. It interacts with I2 of I3- to form charge transfer complex, thereby prevents the sublimation of I2 [8, 9, 13]. Benzoguanamine decreases I3- concentration while it increases I- concentration [13, 15]. Due to decrease in I3-concentration, the reaction decreases between I3- at TiO2 semiconductor electrolyte junction and injected electron, thereby increases the electron concentration [13, 16]. Figure 1.6 shows the power conversion efficiency variations of DSSCs with benzoguanamine doped PVDF/KI/I2 electrolytes. The interaction between the benzoguanamine and PVDF/KI/I2 is shown in Fig. 1.7. The DSSC with 20% benzoguanamine doped PVDF/KI/I2 electrolyte has the highest power conversion efficiency. This may be due to the lowest crystallinity and the highest ionic conductivity of the 20% benzoguanamine doped PVDF/KI/I2 electrolyte.
Table 1.2 The photovoltaic parameters of DSSCs with benzoguanamine (a) 0%,
(b) 10%, (c) 20%, (d) 30%, (e) 40% and (f) 50% doped PVDF/KI/I2 electrolytes
DSSC
|
Benzoguanamine
(%)
|
Jsc (mA/cm2)
|
Voc (V)
|
FF
|
η (%)
|
a
|
0
|
5.50
|
0.72
|
0.38
|
1.5
|
b
|
10
|
6.28
|
0.71
|
0.43
|
1.9
|
c
|
20
|
8.34
|
0.69
|
0.49
|
2.8
|
d
|
30
|
7.95
|
0.70
|
0.46
|
2.5
|
e
|
40
|
7.48
|
0.73
|
0.42
|
2.3
|
f
|
50
|
6.86
|
0.72
|
0.42
|
2.1
|