FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
Inexpensive solution based fabrication method for solar cell
APPLICANT(S):
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR(S):
Roy Pradip and Gaurav Shukla; both of Crompton Greaves Ltd., Advance material Process and Technology Centre, CG Global R&D Centre, Kanjurmarg (E), Mumbai - 400042, Maharashtra, India; both Indian Nationals.
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION :
This invention relates to the field of solar/photovoltaic cells.
Particularly, this invention relates to an inexpensive solution based fabrication method for Solar Cells.
More specifically, this invention relates to an inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSC).
BACKGROUND OF THE INVENTION:
Photovoltaic (PV) cell is a device that converts light energy into electrical energy. Harnessing solar energy with inexpensive materials and manufacturing methods is an important challenge. Low cost deposition techniques and new designs of PV devices are needed to reduce the production costs.
Crystalline and amorphous silicon based solar cells are already available in market providing 4-10% basic cell level conversion efficiency of solar light which can be further enhanced by using external light concentrators and other devices. However, silicon based solar cells are less preferred due to costly manufacturing infrastructure requirements as well as high development and processing costs. A cheaper alternative to silicon based solar cell technology is metal oxide like Titanium oxide (Ti02) based solar cells. T1O2 based solar cells can be categorized into dye sensitized solar cells (DSSC) and quantum dot sensitized solar cell (QDSSC). QDSSC are preferred over DSSC due to their high temperature stability and longer life time. Currently, Ti02 based QDSSC have quite low light to

electricity conversion efficiency, mostly in the range of 0.5 to 2 %. Low efficiency means that larger arrays are needed and that means higher cost. Improving solar cell efficiencies while holding down the cost per cell is an important goal of the PV industry. To enhance the efficiency of QDSSC, materials properties can be tailored by attaching visibly absorbing nano materials with Ti02 for quantum confinement of solar light while retaining efficient transport of electrons.
The performance of a solar cell is measured in terms of its efficiency at turning sunlight into electricity. Only sunlight of certain energies will work efficiently to create electricity, and much of it is reflected or absorbed by the material that makes up the cell Further, the visible radiation forms the largest part of sunlight spectra, it is extremely important to use methods to harness visible light excitation rather than traditional ultra-violet excitation. It is very obvious that exploiting visible region will definitely enhance the light to electricity conversion efficiencies of QDSSC.
Dye sensitized and amorphous silicon based solar cells are already in market providing 4 to 10% conversion efficiency of solar light. To further enhance the conversion efficiency, Quantum dot-sensitized solar cells (QDSSCs) were proposed and described in various patent applications.
Quantum dot-sensitized solar cells (QDSSCs) are interesting energy devices because of their impressive ability to harvest sunlight and generate multiple electron/hole pairs, ease of fabrication, and low cost.
US 2010288345 disclose fabrication of QDSSC using physical vapor deposition (PVD) such as vacuum coating equipment, co-sputtering. The optical active layer

comprises amorphous silicon (a-Si), microcrystalline silicon (uc-Si), copper indium gallium diselenide (CIGS), copper indium diselenide (CIS), copper gallium diselenide (CGS), copper gallium ditelluride (CGT), copper indium aluminium diselenide (CIAS), II-VI or III-V semiconductor. In this, the band gap of the quantum dots is selected from one or more than one of an infrared (IR) range, a visible light range and an ultraviolet (UV) range. If the band gap of the quantum dots is in the IR range, a material of the quantum dots is one or a plurality of substances selected from a substance group consisting of PbS, GaSb, InSb, InAs and CIS; If the band gap of the quantum dots is in the visible light range, the material of the quantum dots is one or a plurality of substances selected from a substance group consisting of indium phosphide (InP) and cadmium sulfide (CdS); and If the band gap of the quantum dots is in the UV range, the material of the quantum dots is one or a plurality of substances selected from a substance group consisting of Ti02, ZnO and Sn02.
CN 101702377 employs zinc nitrate solution as a precursor, zinc oxide (i.e. ZnO) nanorod array on the seed crystal surface and then calcining the ZnO nanorod array for a period of time in a certain temperature to prepare the highly ordered ZnO nanorod electrode, and finally forming a Ti02 membrane on the ZnO nanorod array electrode by a dip-coating method.
Most of the methods to fabricate such QDSSCs are based on deposition of nanocrystalline thin films of Ti02 and an optically active layer containing quantum dots. Thin film deposition using vacuum based techniques is a complex and expensive process.

Thus, in order to commercialize QDSSCs for energy harvesting applications, a need remains to find inexpensive and easy to implement manufacturing process.
Nanocrystalline Ti02 film co-sensitized with Copper indium sulfide (CuInS2) quantum dots (QDs) and Cadmium sulfide (CdS) layers is also known for fabrication of QDSSCs. However, CdS being a toxic material can be harmful. Current developments for creating an inexpensive method for efficient energy harnessing application is a challenge and there is a need to provide a process which in turn can contribute towards the manufacturing of a green technology product.
Also, there remains a need to find inexpensive and easy to implement manufacturing process in order to commercialize QDSSCs for energy harvesting applications.
OBJECTS OF THE INVENTION:
An object of the invention is to provide an inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSC).
Another object of the invention is to provide an inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSC) which enhances the conversion efficiency of solar light.
Yet another object of the invention is to provide an inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSC) which is easy in manufacturing and implementation method.

Yet another object of the invention is to provide an inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSC) which provides quantum confinement of absorbed solar light leading to subsequent enhancement in photo current.
Yet another object of the invention is to provide an inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSC) which provides an efficient medium to absorb visible part of solar spectrum in addition to ultraviolet radiation due to low band gap of CuInS2 and Indium sulfide (In2S3).
Yet another object of the invention is to provide Quantum Dot Sensitized Solar Cells (QDSSC) which enhances the conversion efficiency of solar light.
Yet another object of the invention is to provide Ti02 based Quantum Dot Sensitized Solar Cell (QDSSC) which enhances the cell level light to electricity conversion efficiency of solar light compared to existing Ti02 based quantum dot sensitized solar cells.
Yet another object of the invention is to provide Quantum Dot Sensitized Solar Cells (QDSSC) which is cost-effective.
Yet another object of the invention is to provide Quantum Dot Sensitized Solar Cells (QDSSC) which provides quantum confinement of absorbed solar light leading to subsequent enhancement in photo current.
Yet another object of the invention is to provide Quantum Dot Sensitized Solar Cells (QDSSC) which provides an efficient medium to absorb visible part of solar

spectrum in addition to ultraviolet radiation due to low band gap of CuInS2 and In2S3.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates band diagram for CuInS2/In2S3 co-sensitized Ti02 nanorod arrays (NRA).
Figure 2 illustrates Field Emission Scanning Electron Microscope (FESEM) image of Ti02 nanorod arrays grown on Fluorine tin oxide (FTO) coated glass substrate.
Figure 3 illustrates Transmission Electron Microscope (TEM) analysis of CuInS2 nanocrystals; (a) TEM image of CuInS2 nanocrystals confirming less than 5 nm size of nanocrystals; (b) Lattice image of CuInS2 nanocrystals; (c) selected area diffraction pattern (SAED) of CuInS2 nanocrystals confirming their single crystalline structure.
Figure 4 illustrates Absorption spectra of bare T1O2 nanorod and quantum dot sensitized Ti02 nanorod deposited on FTO coated glass substrate.
Figure 5 illustrates current-voltage characteristics of Ti02 based QDSSC measured under Ammeter (AM) 1.5 G source of 100 mW/cm2 sunlight irradiation.
DETAILED DESCRIPTION OF THE INVENTION:
According to the invention, there is provided an inexpensive Quantum Dot Sensitized Solar Cell (QDSSC);

said cell comprising
a) a nanorod array of metal oxide as core shell on a glass substrate;
b) sensitized nanorod array of metal oxide layer with CuInS2 nanocrystals; and
c) co-sensitized sensitized nanorod metal oxide layer with CuInS2 nanocrystals, with In2S3 to quantum confined nanocrystals onto the nanorod array.
According to the preferable embodiment of the invention, there is provided an inexpensive Quantum Dot Sensitized Solar Cell (QDSSC); said cell comprising
a) a nanorod array of metal oxide of Ti02 as core shell on a glass substrate;
b) sensitized nanorod array of metal oxide layer of Ti02 with CuInS2 nanocrystals; and
c) co-sensitized sensitized nanorod metal oxide layer of Ti02 with CuInS2 nanocrystals, with In2S3 to quantum confined nanocrystals onto the nanorod array.
More preferably, Quantum Dot Sensitized Solar Cells (QDSSC) comprising CuInS2 has a band of approximately 1.5 eV, In2S3 has a band gap of approximately 2.1 eV and Ti02 has a band gap of approximately 3.1 eV.
Figure 1 illustrates band diagram for CuInS2/In2S3 co-sensitized Ti02 nanorod arrays where nanocrystals of CuInS2 coated with In2S3 layer provides quantum confinement of absorbed solar energy. The three level conduction band bridge provides enhanced transport of electrons which in turn increases the light to electricity conversion efficiency.

According to this invention, there is also provided an inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSC); said method comprises;
A. growing nanorod array of metal oxide as core shell on a substrate;
B. sensitization of the nanorod metal oxide layer with CuInS2 nanocrystals and
C. co-sensitization of sensitized nanorod metal oxide layer with CuInS2
nanocrystals, with In2S3 to quantum confined nanocrystals onto the
nanorods.
According to preferable embodiment of this invention, there is also provided the inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSC); said method comprises;
A. growing nanorod array of metal oxide of Ti02 as core shell on a substrate;
B. sensitization of the nanorod metal oxide layer of Ti02 with CuInS2
nanocrystals; and
C. co-sensitization of sensitized nanorod metal oxide layer of Ti02 with CuInS2
nanocrystals, with In2S3 to quantum confined nanocrystals onto the
nanorods.
Preferably, the substrate used in the invention is glass, more preferably, FTO coated glass substrate.
According to one of the embodiments of the invention, there is provided the inexpensive solution based fabrication method to grow In2S3/CuInS2 co-sensitized Ti02 nanorod arrays comprising a glass substrate covered with Fluorine Tin Oxide (FTO) using the following steps;

A. growing a nanorod metal oxide layer of TiO2 on a FTO coated glass
substrate;
B. sensitization of the nanorod metal oxide layer of TiO2 with CuInS2 by
growing its nanocrystals over it; and
C. co-sensitization of the layer obtained in step (ii) with In2S3 to achieve
quantum confinement of incident solar light via Successive Ionic Layer
Adsorption and Reaction.
According to this invention, there is provided the inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSCs) where CuInS2 nanocrystals are grown on Ti02 nanorods to sensitize nanorod metal oxide layer of Ti02 with CuInS2 nanocrystals.
According to this invention, there is provided the inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSCs) where CuInS2 nanocrystals are coated with In2S3 to co-sensitize, sensitized nanorod metal oxide layer of Ti02 with CuInS2 nanocrystals,.
According to this invention, there is provided the inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSCs) where CuInS2 nanocrystals are grown on Ti02 nanorod array followed by thin coating of In2S3 with Succession Ion Layer Absorption and Reaction Method.
According to this invention, there is provided a method to make In2S3/CuInS2 co-sensitized Ti02 core shell QDSSC, where Indium Sulphide acts as optically active layer containing nanocrystals of CuInS2. The CuInS2 has a band of approximately 1.5 eV and In2S3 has a band gap of approximately 2.1 eV while Ti02 has a band

gap of approximately 3.1 eV. Nanocrystals of CuInS2 coated with In2S3 layer provides quantum confinement of absorbed solar light as shown in the band diagram for CuInS2/In2S3 co-sensitized Ti02 nanorod arrays in the figure 1. The three level conduction band bridge provides enhanced transport of electrons which in turn increases the light to electricity conversion efficiency. According to the invention, the nanorod metal oxide layer can be suitable metal oxide layer but preferably a layer of Ti02 nanorod arrays is advised.
According to one of the embodiments of the invention, In2S3/CuInS2 co-sensitized Ti02 core shell rods can be used for fabrication of QDSSCs using standard procedure.
According to the invention, growing of nanorod arrays of Ti02 as in step (A) is
carried out by:
i) preparing a growth solution by mixing Titanium tetraisopropoxide (TTIP),
HC1, glacial acetic acid and water in the ratio of 0.2:1:2:2 (by volume); ii) placing a piece of fluorine tin oxide (FTO) coated glass substrate against the
wall of a teflon-lined reactor filled with the growth solution as obtained in
step (i) at a temperature of 150°C to 170°C for about 5 to 6 hours; iii) removing and rinsing the glass substrate with deionized water on attending
the growth of nanorod arrays of Ti02on the glass substrate, and iv) finally annealing the glass slide at 450°C to 500°C for about 1 hour.
The length of the nanorod array of Ti02 achieved by the present invention is atleast 3 μm.

Nanorod length is very important parameter in order to further enhance the efficiency of QDSSCs, for longer nanorods the conversion efficiency is expected to be higher. The Field Emission Scanning Electron Microscope (FESEM) image of Ti02 nanorod arrays grown on FTO coated glass substrate of the invention confirmed excellent vertical orientation of nanorods as shown in Figure 2. Ti02 nanorod length was found to be ~ 12μm and average diameter of a single nanorod ~ 200 run.
According to the invention, sensitization of the nanorod arrays of Ti02 as in step
(B) is carried out by:
v) mixing 0.1 millimolar of Indium Acetate [In(OAc)3], 0.11 millimolar of Cul
and 0.5 millimolar Thiourea with 0.6 ml of 1-butylamine and 40 ul of 1-
propionic acid; vi) shaking the mixture of step (v) for 1 minute; vii) spin coating the mixture of step (vi) onto the glass substrate covered with
Ti02 nanorod arrays as obtained in step (iv); viii) calcinating the coated glass substrate at 150°C to 170°C for 10 minutes and
then keeping at 250°C to 270°C for 10 minutes; and ix) annealing the calcined coated glass substrate at 450°C to 500°C for 30
minutes in order to increase contact between CuInS2 crystals and Ti02
nanorod arrays.
For the quantum confinement of incident solar light (which will in turn enhance the conversion efficiency of QDSSC), size of CuInS2 is very important and ideally should be less than 5 run. To confirm the size of CuInS2 nanocrystals, Transmission Electron Microscope (TEM) analysis was performed. Figure 3 a shows TEM image of CuInS2 nanocrystals confirming less than 5 nm size of

nanocrystals. Figure 3b shows lattice image of CuInS2 nanocrystals which indicate uniform distribution of nanocrystals with spacing dl 12 is 0.32 nm and d200 is 0.28 nm. Figure 3c shows their single crystalline structure via selected area diffraction pattern (SAED) of CuInS2 nanocrystals and thus results in the quantum confinement of incident solar light which will in turn enhance the conversion efficiency of QDSSC.
According to the invention, co-sensitization with In2S2 to quantum confined
nanocrytals as in step (C) is carried out by:
x) dipping the sensitized glass substrate as obtained in step (ix) in a mixture of
0.05M solution of InCl3 and G.G3M solution of Na2S for 30 seconds; xi) rinsing the slides as obtained in step (x) with deionized water for 30 seconds;
and xii) annealing the glass slides as obtained in step (xi) at 240°C to 260°C for 1
hour.
The absorption spectra of bare Ti02 nanorod arrays and quantum dot sensitized Ti02 nanorod arrays deposited on FTO coated glass substrate was measured using a UV-VIS spectrometer as shown in Figure 4. Absorption spectra confirmed UV absorption maximum of Ti02 near 380 nm (- 3.2 eV) (according to example 1) which gradually changed towards visible region upon incorporation of CuInS2 (according to example 2) and CuInS2/In2S3 nanocrystals (according to example 3). Maximum visible spectrum absorption was observed for Ti02 nanorod arrays co-sensitized with In2S3 and CuInS2.
According to the invention there is provided an inexpensive solution based method to manufacture Ti02 based Quantum Dot Sensitized Solar Cell (QDSSC) where

efficiency of the cell is improved to at least 2.92% via co-sensitization of CuInS2 nanocrystals and In2S3 layer.
The following experimental examples are illustrative of the invention but not limitative of the scope thereof:
Example 1:
A growth solution was prepared by mixing Titanium tetraisopropoxide (TTIP), HO, glacial acetic acid and water in the ratio of 0.2:1:2:2 (by volume). A piece of fluorine tin oxide (FTO) coated glass slide was placed against the wall of a teflon-lined reactor filled with 25mf of the above solution at a temperature of 160°C for about 6 hours. On attending the growth on the glass slide, it was removed and rinsed with deionized water, and finally annealed at 450°C for about 1 hour.
The Field Emission Scanning Electron Microscope (FESEM) image of Ti02 nanorod arrays grown on FTO coated glass confirmed excellent vertical orientation of nanorods as shown in Figure 2. T1O2 nanorod length was found to be ~ 12 um and average diameter of a single nanorod ~ 200 nm.
Example 2:
0.1 millimolar of Indium Acetate [In(OAc)3] was mixed with 0.11 millimolar of Cul, 0.5 millimolar Thiourea, 0.6 ml of 1-butylamine and 40 μl of 1-propionic acid. This mixture was shaken for 1 minute. The mixture obtained was spin coated onto the glass slide prepared according to Example 1. The sample was calcinated at 160°C for 10 minutes and then kept at 260°C for 10 minutes and annealed at 500°C for 30 minutes in order to increase contact between CuInS2 crystals and Ti02 nanorods.

To confirm the size of CuInS2 nanocrystals, Transmission Electron Microscope (TEM) analysis was performed. Figure 3 a shows TEM image of CuInS2 nanocrystals confirming less than 5 nm size of nanocrystals. Figure 3b shows lattice image of CuInS2 nanocrystals which indicate uniform distribution of nano crystals with spacing dl 12 is 0.32 nm and d200 is 0.28 nm. Figure 3c shows their single crystalline structure via selected area diffraction pattern (SAED) of CuInS2 nanocrystals and thus results in the quantum confinement of incident solar light which will in turn enhance the conversion efficiency of QDSSC.
Example 3:
The sensitized glass prepared in accordance with example 1 and 2 was dipped in a mixture comprising 0.05M solution of InCl3 and 0.03M solution of Na2S for 30 second. The samples were rinsed with deionized water for 30 seconds and the glass slides were annealed at 250°C for 1 hour.
The absorption spectra of FTO coated glass slides prepared according to the examples 1 to 3 were measured using a UV-VIS spectrometer as shown in Figure 4. Absorption spectra confirmed UV absorption maximum of Ti02 near 380 nm (~ 3.2 eV) (according to example 1) which gradually changed towards visible region upon incorporation of CuInS2 (according to example 2) and CuInS2/In2S3 nanocrystals (according to example 3). Maximum visible spectrum absorption was observed for Ti02 nanorod arrays co-sensitized with In2S3 and CuInS2.
Three FTO coated glass electrodes were prepared according to the examples 1 to 3 to prepare the FTO glass electrode covered with Ti02 nanorod arrays, FTO glass electrode covered with Ti02 nanorod arrays and coated with CuInS2 crystals and FTO glass electrode covered In2S3/CuInS2 co-sensitized Ti02 nanorod arrays.

These electrodes were further used to examine a photo-voltaic performance against platinum coated FTO glass counter electrode. A hot melt spacer (100 urn, Dupont, Surlyn 1702) was used. An acetonitrile/valeronitrile (85/15 v/v) electrolyte was used containing 0.6 M 1, 2-dimethyl 3-propyllimidazonium iodide, 0.03 M I2, 0.1 M guanidinium thiocynate and 0.5 M 4-tert-butylpyridine. The current-voltage characteristics of Ti02 based QDSSC were measured under AM 1.5 G source of 100 mW/cm2 sunlight irradiation with a CHI-660D electrochemical analyzer. The active cell area was estimated to be around 0.2 cm2. The results are shown in Figure 5 which confirmed the superior performance of Ti02 nanorod arrays co-sensitized with In2S3 and CuInS2. The comparative photovoltaic performance for Ti02 nanorod based solar cells ie,_Ti02 nanorod arrays co-sensitized with rn2S3 and CuInS2 (according to example 3), bare Ti02 nanorod array based solar cell (according to example 1) and only CuInS2 nanocrystals sensitized QDSSC (according to example 2). The comparative conversion efficiencies of all three electrodes are provided in Table 1.
Table 1 Comparative photovoltaic performance for TiO2 nanorod based solar cells

Type Jsc Voc(V) Fill factor Efficiency
(mA/cm2 ) (%) ŋ(%)
Ti02 Nanorod array 3.74 0.37 32 0.43
(according to example 1)
Ti02 Nanorod array + 4.19 0.52 40 1.06
CuInS2 nanocrystals
(according to example 2)
Ti02 Nanorod array + 5.52 0.66 53 2.92
CuInS2 nanocrystals + In2S3
(according to example 3)

The conversation efficiency of Ti02 nanorod arrays co-sensitized with In2S3 and CuInS2 (according to example 3) increased by 600% compared to bare Ti02 nanorod array based solar cell (according to example 1) and ~ 300% for only CuInS2 nanocrystals sensitized QDSSC (according to example 2). These results confirm the importance of conduction band bridging and quantum confinement of incident light via In2S3 layer in enhancing the light to electricity conversion efficiency of Ti02 based QDSSC.
The present invention provides efficient medium to absorb visible part of solar spectrum in addition to ultraviolet radiation due to low band gap of CuInS2 and In2S3. It also provides quantum confinement of absorbed solar light leading to subsequent enhancement in photo current. This leads to enhancement of the conversion efficiency of solar light and makes the method and solar cell cost-effective.
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We Claim,
1. An inexpensive Quantum Dot Sensitized Solar Cell (QDSSC);
said cell comprising
a) a nanorod array of metal oxide as core shell on a substrate;
b) sensitized nanorod array of metal oxide layer with CuInS2 nanocrystals; and
c) co-sensitized sensitized nanorod metal oxide layer with CuInS2 nanocrystals, with In2S3 to quantum confined nanocrystals onto the nanorod array.
2. The Quantum Dot Sensitized Solar Cells (QDSSC) as claimed in claim 1;
wherein particularly said cell comprising
a) a nanorod array of metal oxide of Ti02 as core shell on a substrate;
b) sensitized nanorod array of metal oxide layer of Ti02 with CuInS2 nanocrystals; and
c) co-sensitized sensitized nanorod metal oxide layer of Ti02 with CuInS2 nanocrystals, with In2S3 to quantum confined nanocrystals onto the nanorod array.
3. The Quantum Dot Sensitized Solar Cells (QDSSC) as claimed in claims 1 to
2; wherein said cell comprising the CuInS2 has a band of approximately 1.5
eV, UI2S3 has a band gap of approximately 2.1 eV and Ti02 has a band gap
of approximately 3.1 eV.

4. The Quantum Dot Sensitized Solar Cells (QDSSC) as claimed in claims 1 to 3; wherein the substrate is glass, preferably FTO coated glass substrate.
5. An inexpensive solution based fabrication method for Quantum Dot Sensitized Solar Cells (QDSSC);
said method comprises;
A. growing nanorod array of metal oxide as core shell on a substrate;
B. sensitization of the nanorod metal oxide layer with CuInS2
nanocrystals; and
C. co-sensitization of sensitized nanorod metal oxide layer with CuInS2
nanocrystals, with In2S3 to quantum confined nanocrystals onto the
nanorods.
6. The solution based fabrication method for Quantum Dot Sensitized Solar
Cells (QDSSC);
particularly said method comprises;
A. growing nanorod array of metal oxide of Ti02 as core shell on the
substrate;
B. sensitization of the nanorod metal oxide layer of Ti02 of the substrate
with CuInS2 nanocrystals; and
C. co-sensitization of sensitized nanorod metal oxide layer of Ti02 with
CuInS2 nanocrystals of the substrate, with In2S3 to quantum confined
nanocrystals of CuInS2 and In2S3onto the nanorods.
7. The solution based fabrication method for Quantum Dot Sensitized Solar
Cells (QDSSC) as claimed in claims 5 to 6; wherein the substrate is glass,
preferably FTO coated glass substrate.

8. The solution based fabrication method for Quantum Dot Sensitized Solar
Cells (QDSSC) as claimed in claims 5 to 7; wherein the growing of nanorod
arrays of Ti02 as in step (A) is carried out by:
i) preparing a growth solution by mixing Titanium tetraisopropoxide
(TTIP), HC1, glacial acetic acid and water in the ratio of 0.2:1:2:2 (by
volume); ii) placing a piece of fluorine tin oxide (FTO) coated glass substrate
against the wall of a teflon-lined reactor filled with the growth solution
as obtained in step (i) at a temperature of 150°C to 170°C for about 5 to
6 hours; iii) removing and rinsing the glass substrate with deionized water on
attending the growth of nanorod arrays of Ti02on the glass substrate,
and iv) finally annealing the glass slide at 450°C to 500°C for about 1 hour.
9. The solution based fabrication method for Quantum Dot Sensitized Solar
Cells (QDSSC) as claimed in claims 5 to 7; wherein the sensitization of the
nanorod arrays of Ti02 as in step (B) is carried out by:
v) mixing 0.1 millimolar of Indium Acetate [In(OAc)3], 0.11 millimolar
of Cul and 0.5 millimolar Thiourea with 0.6 ml of 1-butylamine and
40 μl of 1-propionic acid; vi) shaking the mixture of step (v) for 1 minute; vii) spin coating the mixture of step (vi) onto the glass substrate covered
with Ti02 nanorods arrays as obtained in step (iv); viii) calcinating the coated glass substrate at 150°C to 170°C for 10
minutes and then keeping at 250°C to 270°C for 10 minutes; and

ix) annealing the calcined coated glass substrate at 450°C to 500°C for 30 minutes in order to increase contact between CuInS2 crystals and Ti02 nanorod arrays.
10. The solution based fabrication method for Quantum Dot Sensitized Solar
Cells (QDSSC) as claimed in claims 5 to 7; wherein the co-sensitization
with In2S2 to quantum confined nanocrytals as in step (C) is carried out by:
x) dipping the sensitized glass substrate as obtained in step (ix) in a
mixture of 0.05M solution of InCl3 and 0.03M solution of Na2S for 30
seconds; xi) rinsing the substrate as obtained in step (x) with deionized water for 30
seconds; and xii) annealing the glass substrate as obtained in step (xi) at 240°C to 260°C
for 1 hour.
11. The Quantum Dot Sensitized Solar Cells (QDSSC) as claimed in claims 1 to
4 prepared according to the methods as claimed in claim 5 to 10where
efficiency of the cell is improved to 2.92 % via co-sensitization of CulnS2
nanocrystals and In2S3 layer of Ti02 nanorod arrays.