Department of Chemistry, Institute of Science, Banaras Hindu University Varanasi 221005, India

TNP
200 nm
G -TNP
200 nm
Solar Energy 194 (2019) 952–958
956
50 nm
Fig. 5. HR-SEM images of TNP and G-TNP.
Fig. 6. HRTEM images of TNP and G-TNP.
IC Maurya, et al.
16 ± 2 nm, while, G-TNP nanoparticles exhibited irregular spherical
morphologies and rougher surfaces with average particle size of 13 ± 2
nm. It is therefore clearly evident that B. orellana has both stabilization
and capping action which influence the morphology, mi crostructures and
size of synthesized TiO2 nanoparticles. HRTEM images also confirmed
similar morphological characteristics with mesoporous structures,
consisting of connections and highly crystallized TiO2 nanoparticles with
average diameter of 15 nm and 13 nm for TNP and G-TNP respectively
(Fig.
6).
Altogether, XRD, HRSEM and HRTEM analyzes thus demonstrated
that the employed green synthesis technique is a very useful method for
the synthesis of nano-sized pure anatase TiO2 nanoparticles (G-TNP)
with mesoporous structural characteristics. Since mesoporous pure
anatase phase of TiO2 has the greatest potential for charge transfer and
dye adsorption, the developed G-TNP could be used for the develop ment
of an efficient DSSC system.
3.3. Photovoltaic performances
From optical properties, structural characteristics and BET analysis it
is observed that the TiO2 nanoparticles synthesized using B. orellana (G-
TNP) have nanoscale structure having pure anatase phase with
mesoporous structures, now it is relevant to investigate these effects on
photovoltaic performances.
Fig. 8
showed the typical photocurrent voltage
(JV) characteristic curves of N719-sensitized TNP and G-TNP based solar
cells measured at one sun light intensity. The photovoltaic output
parameters, such as, photocurrent density (JSC), open-circuit voltage
(VOC), fill factor (FF) and overall cell efficiency ( ), of the DSSCs are
summarized in
Table
2. The N719 carboxylic acids adsorption on TiO2
surface either due to rapid proton shuttling between carboxylic acid and
surface oxygen or proton sharing consequent to quantum de localization
is of prime importance in the functionality of DSSC
(Tabacchi et al., 2019).
The JSC value has been found to be greatly improved from 2 to 9 mA/
cm2 using the G-TNP based DSSC devices as compared to the TNP
based devices, whereas a little decrease in the open circuit voltage (VOC)
from 0.680 to 0.506 V revealed a faster electron recombination in G-TNP
compared to TNP cell. Consistent with the increment of JSC values, much
higher cell efficiency was obtained for G-TNP (2.97%) as compared to
TNP (1.03%) based cell.
Surface area, pore volume and porosity of TNP and G-TNP were
evaluated by nitrogen adsorption/desorption (BrunauerÿEmmett ÿTeller or
BET) measurements as shown in
Fig.
7a and
Table
1. The results showed
a type IV isotherm and H3 hysteresis loops characteristic for mesoporous
material with slit-shaped pores according to IUPAC classification for both
TNP and G-TNP. Pore size distribution of the
As shown in
Fig.
8a, the dark current density of TNP cell is much
higher than that of G-TNP cell, indicating that a serious electron re
combination phenomenon is probably happening at the interface
materials based on nitrogen adsorption/desorption isotherm was eval
uated by the BarrettÿJoynerÿHalenda (BJH) method as shown in
Fig.
7b.
The BJH curve revealed average pore size was 5.4 and 10.6 nm for TNP
and G-TNP respectively with narrow distribution. The BET surface area
and total pore volume of TNP and G-TNP nanoparticles were determined
to be 80 and 100 m2 /g; and 0.1622 and 0.2151 cm3 /g respectively. The
nitrogen adsorption/desorption measurement results therefore confirmed
that the TiO2 NPs synthesized using green synthesis
technique have mesoporous structure with the large surface area and
increased pore size, which enhance the dye loading efficiency and thus
could play a significant role in the enhancement of overall performance of
the DSSCs.

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