SUPPLIMENTARY MATERIAL
CONCEPT AND DEMONSTRATION OF ALL ORGANIC GRATZEL
SOLAR CELL (DYE SENSITIZED SOLAR CELL)
Prakash R. Somani (*), Savita P. Somani, M. Umeno
Department of Electronics and Information Engineering, Chubu University, 1200
Matsumoto-cho, Kasugai 487-8501, Japan
A. Sato
Department of Applied Chemistry, Chubu University, 1200 Matsumoto-cho,
Kasugai 487-8501, Japan.
-----------------------------------------------------------------------------------------------------------* Author for correspondence
 E mail : psomani_cmetp@yahoo.com / psomani1@yahoo.com
Experimental Details :
Microwave assisted surface wave plasma chemical vapor deposition (MW-SWP-CVD) is
used to deposit a-C:H films doped with nitrogen (a-C:H-N) using C2H2 as a source gas,
Ar as carrier gas and N2 for doping. More detailed experimental procedure for deposition
of such films is described in Reference [16]. Typical microwave power used for
generating the plasma ranged between 500 to 600 W. The temperature of the substrate at
the start of the deposition varied from 27 to 120 oC. Before deposition, the chamber was
evacuated to about 7 X 10-4 Pa. The deposition pressure in the chamber, which is mainly
due to Ar, was varied from 16 to 76 Pa by changing the flow rate of Ar from 25 to 400
sccm. The flow rates of C2H2 and N2 gases were kept constant at 1.5 and 5 sccm. a-C:HN films were deposited simultaneously on indium-tin-oxide (ITO) coated glass and
quartz (QZ) substrates (2 X 2 cm2). Reflectance and transmittance measurements were
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performed on a-C:H-N films deposited on ITO and QZ substrates using JASCO V570 UV-VIS-NIR spectrophotometer keeping appropriate substrates as reference. Tauc plot is
plotted and the Tauc optical band gap is estimated for the films deposited on both ITO
and QZ substrates. Basically, this optical gap is a measure of the gap between the
extended states in the valance and conduction bands. It is known that the absorption of
ITO starts below 350 nm. For films deposited on ITO, part of the Tauc curve above 3.8
eV is not taken into account considering the fact that ITO starts absorption below 350 nm
whereas for the films deposited on QZ, the whole curve is taken into consideration. In
general, it has been found that the Tauc band gap of the films deposited on ITO substrates
is higher by 0.2 to 0.3 eV as compared to the corresponding films deposited on QZ
substrates. The reason for such higher Tauc band gaps on ITO films becomes clear when
we have studied all samples by Energy Dispersive X-Ray Analysis (EDAX). It was
found that the actual amount of C content (at. wt. %) is lower (considering content of N)
for the films deposited on ITO substrates; compared with the corresponding films on QZ
substrates. For example, for the film discussed in Figure (1) : On ITO : C, N and O
content detected by EDAX is about 17.86, 26.75 and 55.39 at. % respectively with N/C
ratio of about 1.497 while on QZ : C, N, O detected are 42.0, 36.0 and 22.0 at. %,
respectively with N/C ratio of about 0.8 only. Higher oxygen content detected on ITO
substrates may be partially originating from the oxide substrate. Films with higher Tauc
band gaps (above 2.5 eV) on ITO are used for further experiments.
Cupper Phthalocyanine (Cu-PhTh, Aldrich) thin films were deposited on ITO/a-C:H-N,
QZ/a-C:H-N and QZ films by resistive heating and vacuum evaporation technique.
Typical thickness of Cu-PhTh film was about 250 nm. The composite bi-layer films of a-
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C:H-N and Cu-PhTh films on ITO and QZ are again studied by UV-VIS-NIR
spectrophotometer for their optical absorption. Some of the films are coated with a thin
film of gold (50 nm) so as to make a sand-witch configuration (ITO/a-C:H-N/CuPhTh/Au). Current-Voltage (I-V) measurements were performed on such sand witch cells
in order to study the charge transport mechanism in a-C:H-N/Cu-PhTh bilayer films.
Cyclic voltammetry (CV) measurements were performed in dark and under white light
illumination (60 W, tungsten source) using ITO/a-C:H-N/Cu-PhTh (and ITO/a-C:H-N)
films as working electrodes, Ag/AgCl reference electrode and Pt – counter electrode (in
the form of a thin wire) on Solartron PG stat. The liquid electrolyte used was either
aqueous solution of iodine (3 M KI + 0.01 M I2) or LiPF6 in dimethyl carbonate (DMC)
(1 M /L, 1:2 Volume, Chameleon Reagent).
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Current-Voltage (I-V) characteristics of ITO/a-C:H-N (2.85 eV)/Cu-PhTh (250 nm)
/ Au cell displaying the linear behavior.
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Schematic of the Photoelectrochemical (PEC) solar cell measurement set-up using
ITO/a-C:H-N/Cu-PhTh films and liquid electrolyte (either LiPF6/DMC or aqueous
iodine solution).
Pt is used as counter electrode while Ag/AgCl as Reference
electrode.
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Rising portion of the cyclic voltammetery is plotted as an I-V curve in dark and
light for the ITO/a-C:H-N/aq. Iodine / Pt (counter electrode) configuration, with
open circuit voltage of about 0.18 V. I-V curves in dark and light are same.
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