Synthesis of CdS spongy balls with nanoconduits for ...shodhganga.inflibnet.ac.in/bitstream/10603/4064/10/10_chapter 4.pdf · employing semiconductor-redox systems have been extensively

CHAPTER-IV

Synthesis of CdS spongy balls

with nanoconduits for effective

light harvesting

Chapter-IV Synthesis of CdS spongy ball………………….. light harvesting

107

4.1Outline:

Cadmium sulphide (CdS) thin films consisting of spongy balls with

nanoconduits have been chemically synthesized at 70 oC from an aqueous

alkaline bath on soda lime glass and fluorine doped tin oxide coated glass

substrates. The synthesized CdS spongy balls were characterized using X-ray

diffraction (XRD), UV-Visible spectroscopy, Scanning electron microscopy

(SEM), Fourier transform Raman spectroscopy (FTIR), X-ray photoelectron

spectroscopy (XPS) techniques. The XRD reveals cubic crystal structure with

no impurities or sub stiochiometric phases. The SEM study revealed novel

spongy ball-like morphology comprising of nanoconduits. Such spongy balls

with nanoconduits containing numerous nanowalls are a facile way for the

light trapping. The light absorption path length of photon increased as in the

nanoconduits and gets multiple scattering and absorption. This is beneficial

for effective light harvesting and improvement of photoelectrochemical (PEC)

properties.

CHAPTER

IV

Synthesis of CdS spongy balls with

nanoconduits for effective light harvesting 4


108

4.2. Introduction

Solar energy is converted into electrical energy by using solid state

(photovoltaic) semiconductor solar cells. These solar cells are manufactured

as a rule from highly pure and perfectly crystalline materials and p-n junctions

are obtained by using sophisticated technology. For this reason, these cells

are still very costly, which does not permit their wide applications. PEC cells

employing semiconductor-redox systems have been extensively studied in

recent years because of their potentially significant advantages over solid

state photovoltaic cells. Firstly, a PEC solar cell is much cheaper than the

traditional solid state cells. Secondly, in PEC cell electrical contact for solar

energy applications is formed as soon as the semiconductor electrode is

immersed in the electrolyte. Third, by the proper choice of redox couple in the

electrolyte, the Fermi level in the electrolyte can be controlled and thus the

barrier height can be adjusted to the desired level. Other advantage of PEC

system is due to its photoelectrolysis version in which light energy is directly

converted into chemical energy which can be used to solve the problem of

energy storage. The PEC performance of thin film material depends on high

surface area, morphological features like size, shape, grain boundaries,

number of active insertion sites, film thickness, crystallite size and

interconnected particles [1-3]. It is also noted that, the morphology with

complex nanostructures is potentially even more interesting for the

applications of solar energy harvesting and conversion [4].

Metal chalcogenides (sulphide, selenide and telluride) have been

studied intensively over the past sixty years in view of their potential

applications in PEC, gas sensors and other optical devices [5-6]. The metal

chalcogenide thin films, of CdS, are one of the important examples of thin film

semiconductor electrodes. The CdS nanocrystalline thin films used as

promising material for CdS/CdTe solar cells continues to be a subject of

intense research [7-11]. The CdS with cubic structure is favorable for solar

cell application because of its suitable band gap (2.4 eV) which cover solar

spectrum in visible region. Recently, CdS nanoparticles are applied to

quantum dot sensitized photoelectrochemical cells to improve their

performance [12-14]. However, despite the widespread interest in CdS, it is


109

very hazardous in nature. Under PEC conditions, it degrades into soluble Cd2+

ions, which are dreadfully unsafe and environmentally unsociable [15].

Several techniques have been used to fabricate CdS thin films, such

as electrodeposition [16], chemical bath deposition (CBD) [17], spray pyrolysis

technique (SPT) [18], chemical vapor deposition (CVD) [19], vacuum

evaporation method [20] and sputtering [21]. The efficient, low temperature

and low-cost deposition methods of thin films preparations for technological

industrial applications are always welcomed worldwide. CBD is a soft solution

process capable of producing high-quality thin films by adjusting the pH,

temperature and reagent concentrations at relatively low temperature. CBD

method does not require substrate conductivity and stability as in the case of

electro-deposition. It does not form coating complex which may be a problem

in directional growth methods like screen printing and SPT. On the contrary,

Sputtering, CVD, vacuum evaporation etc. methods require specialized

equipments. CBD is a simple and low-cost method to produce uniform,

adherent and reproducible large-area thin films [22]. The fundamental of CBD

growth mechanism involves mass transport of reactants, adsorption, surface

diffusion, reaction, nucleation and growth. Deposition occurs when the ionic

product of ions (both anion and cation) exceeds the solubility product of

solution.

Recent investigations highlighted an attractive approach of light trapping

and its effective harvesting to enhance the efficiency and short circuit

photocurrents of the solar cells based on silicon, ZnO and polymer solar cells.

The term light-trapping refers to the redistribution of the incoming light into

new directions within the solar cell. Ideally, total internal reflection will then

prevent this redirected light from escaping the solar cell [23]. The efforts have

been made to increase light trapping in solar cells either by creating suitable

morphology or by using V-shaped structure [24-25]. Consequently, the light-

trapping path length can be increased above the Lambertian limit for

enhanced absorption. Another way to increase the efficiency is to increase the

light-harvesting capability of the photoelectrode film by utilizing optical

enhancement effects, which can be achieved by means of light scattering.

The light scattering influences the transport behavior of light through changing


110

or extending the distance of light traveled within the photoelectrode film, and

thus the light-harvesting efficiency gets improved due to the increased

probability of interaction between the photons and nanocrystallites. [26-29]

In this chapter, attempts have been made to engineer the morphology

of the CdS thin film to accomplish light trapping, scattering and maximum

absorption. Their subsequent effects on enhancing photocurrent and

efficiency have been examined. The novel CdS spongy balls with

nanoconduits are prepared at 70 oC by using the CBD method on soda lime

glass and fluorine doped tin oxide (FTO) coated glass substrates. The

preparative parameters are controlled and adjusted to get better morphology

for light trapping and their structural, optical and PEC properties are

addressed.

4.3. Experimental details

All chemical were purchased from s. d. fine chemicals, Mumbai and

used without any further purification. The cadmium sulfate (3CdSO4·H2O) was

used as cadmium (Cd) source and thiourea (H2N⋅CS⋅NH2) for sulphur (S)

source. Liquor ammonia (NH3) was used as complexing agent. The

preparative parameters like solution concentration, temperature and

immersion time were varied. Finally, a standard recipe was chosen as follows:

aqueous ammonia (NH4OH) was added to maintain the pH to 11 of 1 M

CdSO4 solution. Initial turbid solution is turned to a transparent, by adding

excess ammonia. Excess amount of ammonia supply Cd(NH3)42+ ions to the

solution. Then, 1 M Thiourea (H2N⋅CS⋅NH2) is added to above solution as S2-

precursor. Bath temperature was optimized at 70 oC. The CdS thin films were

deposited by dipping the substrates in to the above solution for 10, 20 and 30

min, and samples are denoted as CdS10, CdS20 and CdS30 respectively. The

deposited CdS films were rinsed with double distilled water, and allowed to

dry at room temperature, in ambient air.

Characterization:

The structural properties of the CdS thin films were studied with XRD

using an X-ray diffractometer (Philips, PW 3710, Almelo, Holland) operated at


111

25 kV, 20 mA with CuKα radiation (1.5407 Å). The Fourier transform Raman

(FT-Raman) spectra of the films were recorded in the spectral range of 250–

1000 cm−1 using FT-Raman spectrometer (Bruker MultiRAM, Germany) that

employs Nd:YAG laser source with an excitation wavelength 1064 nm and

resolution 4 cm-1. The UV–Visible absorbance spectra of CdS thin films were

recorded using a UV–visible spectrophotometer (UV3600, Shimadzu, Japan).

The surface morphology of the films were examined by analyzing the SEM

Model JEOL-JSM-6360, Japan, operated at 20 kV. Field emission scanning

electron microscope (FE-SEM Model: JSM-6701F) was employed for closer

insight into the CdS morphology. The thickness of the resulting CdS thin films

was estimated using surface profiler (Ambios XP-1). The surface morphology

and surface roughness of the films was observed by using atomic force

microscopy (AFM, Digital Instrument, nanoscope III) operated at room

temperature. The chemical composition and valence states of constituent

elements were analyzed by XPS, Physical Electronics PHI 5400, USA) with

monochromatic Mg-Kα (1254 eV) radiation source. The J-V characteristics

were measured using Semiconductor Characterization System SCS-4200

Keithley, Germany using two electrode configurations.

4.4. Results and discussion

4.4.1 Reaction Mechanism:

The precipitation of metal chalcogenides in CBD occurs only when the

ionic product exceeds the solubility product of metal chalcogenides (i.e. CdS

in our case) [30]. Generally, ions combine to form nuclei on the substrate as

well as in the solution and precipitation occurs. The film growth takes place

via ion-by-ion condensation of materials or by adsorption of colloidal particles

from the solution onto the substrate. The complexing agents (like NH3) help to

control the reaction rate. Generally, slow reaction results in adherent and

good quality films. The formation of CdS thin films using ammonia as a

complexing agent proceeds via following steps [31-32].

CdSO4 at 11pH dissociates as:

CdSO4 → Cd2+ + SO4− 2 ------------------------- (4.1)


112

Ammonia dissociates as:

NH4OH → NH3 + H2O ----------------------- (4.2)

Metal complex is formed by combining reactions (4.1) and (4.2),

Cd2+ + 2NH3 → [Cd (NH3)2] +2 ------------------------ (4.3)

Addition of thiourea leads to the release of sulfur ions:

CS(NH2)2 + 2OH− → S2− + CH2N2 + 2H2O ------------------- (4.4)

CdS thin film is formed by virtue of (4.1) and (4.4) reactions:

Cd2+ + S2− → CdS --------------------- (4.5)

In strong basic solution CdS is formed after an intermediate formation

of hydroxide as:

nCd2+ + 2n(OH)− → [Cd(OH)2]n ------------------- (4.6)

[Cd(OH)2]n + nS2− → nCdS + 2nOH− ------------------ (4.7)


113

4.4.2 XRD Study:

Figure (4.1) XRD pattern of CdS spongy balls thin film

The XRD pattern of CdS thin film deposited on FTO coated glass

substrate is shown in Fig. (4.1) for CdS30 sample. The sample exhibit single

phase cubic structure (JCPDS card no. 80-0019). The lattice parameter ‘a’ of

the CdS is determined from the analysis of the XRD pattern and is estimated

from the formula for cubic system (eq.3.1). The mean values of a= 5.810 Å is

in good agreement with the reported value a=5.811Å. The mean crystallite

size of CdS was calculated using the Debye–Scherrer formula (eq.3.2). The

crystallite size of the CdS is about 18 nm. The presence of broad XRD peaks

is an indication of small crystallite size in the nano range, affirming the

nanocrystalline nature of the CdS thin films.


114

4.4.3 FT-Raman Spectroscopy Study:

FT-Raman is a sensitive method of analysis for nanometer sized

crystals [33-34]. The Raman spectrum of the CdS film is shown in Fig. (4.2).

The cubic structured CdS belongs to T2d (F 3m) space group have normal

lattice vibration modes given by

2 2 (4.8)1 1 1 2

A B E Eopt

τ = + + + − − − − − − − − −

where, A1, E1 and E2 are Raman active, where as B1 is forbidden.

900 800 700 600 500 400 300

(899)c

m-1 C

d-S

Str

etc

hin

g LO-1

LO-2

(599)cm-1 Cd-S Stretching

(302)cm-1 Cd-S Stretching

Ram

an

In

ten

sit

y (

a.u

.)

Wavenumber (cm-1)

Figure (4.2) Raman spectrum of CdS spongy balls thin film

The Raman spectrum of the CdS film exhibits a well-resolved band at

302 cm-1, corresponding to the first order scattering of the longitudinal optical

(LO) phonon mode and second-order band around 599 cm-1. CdS can have

both hexagonal wurtzite and cubic zinc blended structures, and it is reported

that for both the structures, the zone-center longitudinal-optical A1 (LO)


115

phonon frequency is nearly 305 cm-1[35-39]. The full width half maximum

(FWHM) of the 1 LO peak is 21.64 cm-1. Though, this large width indicates

poor crystallinity (lack of long-range order) in the films, but the well-defined

peak indicates the crystalline nature of the material. Hence, the large FWHM

in the present case can be attributed to a polycrystalline effect in the as-

deposited film.

4.4.4 Optical Absorption Study:

Fig. 4.3 shows the room temperature optical absorption

spectrum of the CdS films recorded in the range of 500–1100 nm without

taking into account scattering and reflection losses. It can be seen that an

absorption peak at ~ 515 nm is present for all films, representing the bandgap

of ~2.4 eV. By comparing the absorption spectra of the three films, it can be

seen that an additional absorption hump over the visible and NIR region for

the CdS30 sample. This additional absorption is an indication of effective light

scattering. Similar type of results is reported for ZnO thin films [40-41]. The

light scattering ability would enhance the ability of the CdS30 sample to absorb

more of the photons, resulting in an increase in the generation of electron-

hole pairs and an increase in the short-circuit current density, which is in

accordance to previous reports. [42-43].


116

500 600 700 800 900 1000 1100

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.00.0

2.0x103

4.0x103

6.0x103

8.0x103

1.0x104

( αα ααh

νν νν)1

/2 e

V/c

m2

Photon Energy (eV)

CdS10

CdS20

CdS30

CdS30

CdS20

CdS10

Wavelength (nm)

Ab

so

rban

ce (

a.u

.)

Figure (4.3) Room temperature optical absorption spectrum of CdS spongy

balls thin film. Inset shows the band gap determination

4.4.5 XPS Study:

Fig. 4.4(a) shows the survey spectrum of the CdS sample CdS30. No

peaks of other elements except Cadmium (Cd), Sulphur (S), Carbon (C), and

Oxygen (O) are observed. The C and O peaks are mainly from the

atmospheric contamination due to a sample exposure to air. The

unambiguous presence of the Cd3d doublet signal clearly shows the

formation of CdS


117

1200 1000 800 600 400 200 0

(a)XPS of CdS

S2

p

S2

sC1s

Cd

3d

O1

s

Cd

3p

3

Cd

3p

1

Cd

MN

2

Co

un

ts /s

Binding Energy (eV)

Figure (4.4) survey spectrum of the CdS sample CdS30

Fig. 4.4 (b-c) depicts narrow range scans for the Cd and S peak region of

the same samples. The binding energies obtained from in the XPS analysis

have been corrected taking into account the specimen charging and by

referring to C1s at 284.88 eV. The two peak structure in Cd 3d core level

arises from the spin-orbit interaction with the Cd 3d5/2 peak position at 403.75

eV and the 3d3/2 at 410.48 eV. It is clear from the spectral graph that, Cd 3d

exhibits narrow, well defined feature for doublet structure. This suggests that,

specifically Cd atoms appear to bond to S atoms. The XPS binding energies

of Cd 3d3 at 404.14 eV and the S 2p at 160.89 eV are indicative of the CdS

chemistry. These results agree well with those reported in the literature. The

peak originated at 1111.04 eV is due to the auger electron of Cd [44].


118

166 164 162 160 158 156

(b)S2pC

ou

nts

/s

Binding Energy (eV)

416 414 412 410 408 406 404 402 400

Cd

3d

5

Cd

3d

3

(c)

Co

un

ts /s

Binding Energy (eV)

Figure 4.4 (b and c) Narrow range scans for the Cd and S peak region of the

same samples

4.4.6 Surface Morphology Study:

The representative morphologies and structures of CdS spongy balls

were investigated by SEM and FE-SEM and are shown in Fig. 4.5 (a–h). The

low magnification SEM images (a and b) show the formation of CdS spongy

balls deposited over the substrate. The SEM image (c) shows CdS spongy

ball with nanoconduits. The high magnification SEM images of CdS10, CdS20

and CdS30 shown in Fig. 4.5(d to f). These images reveal that the CdS spongy

balls are formed and made up of nanoconduits formed by numerous

nanowalls. These nanowalls are interconnected to each other. Such walls

having ~35 nm thickness are clearly seen in the high magnification FE-SEM

images (g and h).


119

Fig. 4.5 (a–h) CdS spongy balls

(a)

(g)

(c)

(e) (f)

(d)

(b)

(h)


120

Due to these nano-sized walls of spongy balls the surface area of the

film increases. Maximum surface area offered by this morphology is

advantages for effective light harvesting in photoelectrochemical solar cell.

Such spongy balls with nanoconduits containing numerous nanowalls are

effective for the light trapping. The light absorption path length of photons can

be increased as it is trapped in the nanoconduits. These mechanisms boost

the PEC performance of CdS electrode.

4.4.7 Atomic Force Microscopy Study:

Figure (4.6)-(a) AFM image of CdS spongy balls thin film of sample CdS10


121

Figure (4.6)-(b) AFM image of CdS spongy balls thin film of sample CdS30

AFM images Fig. 4.6(a and b) of sample CdS10 and CdS30 reveals a

uniform crack-free, densely packed microstructure. The surface roughness of

the film is calculated to be 1037 nm for the sample CdS30. The AFM images

replicate 3D morphology, complementary to the SEM image.

4.4.8 PEC performance:

For the PEC characterization of the CdS spongy balls, all the measurements

were performed in an electrolyte of 1 M polysulfide (Na2S-NaOH-S) in a two-

electrode arrangement of following configuration:

Glass/FTO / CdS/Na2S-NaOH-S/G

In thin film configuration of photoelectrochemical cell, CdS thin film deposited

on FTO acts as a working electrode (active area ~ 1.2 cm2), and G is graphite

plate, which acts as a counter electrode. The J-V characteristics were

measured by a SCS-4200 unit in the dark and under illumination at 28

mW/cm2. Fig. 7(a-c) shows the J-V characteristics of CdS thin films CdS10,

CdS20 and CdS30.


122

-200 0 200 400-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

CdS10

Photovoltage (mV)

Cu

rre

nt

De

ns

ity

(m

A/c

m2)

Figure.7 (a) Photocurrent-density–voltage curves for sample CdS10

-200 0 200 400 600

-4.0

-2.0

0.0

2.0

4.0CdS

20

Photovoltage (mv)

Cu

rren

t D

en

sit

y (

mA

/cm

2)

Figure.7 (b) Photocurrent-density–voltage curves for sample CdS20


123

-300 -200 -100 0 100 200 300 400 500 600

-4

-2

0

2

4CdS

30

Curr

ent D

ensi

ty

(mA

/cm

2)

Photovoltage (mv)

Figure.7(c) Photocurrent-density–voltage curves for sample CdS30

The J-V characteristic in the dark resembles ideal diode-like rectifying

characteristics for the PEC cells fabricated with all the samples. Upon

illumination, J-V curves shifts in the IVth quadrant indicating generation of

electricity, typical of solar cell characterization. The magnitude of short circuit

current density (JSC) was 1.47, 3.30 and 4.17 mA/cm2 for CdS10, CdS20 and

CdS30 samples respectively. The corresponding open circuit voltage (VOC)

was found to be 372, 375 and 453 mV. This observation reveals that the JSC is

increased three-fold while there is no subsequent rise in the VOC. However,

the shape of the J-V curves is changed substantially. The nearly ideal bulging

type J-V curve for CdS10 sample begins to sag towards the origin for CdS20

and CdS30 samples and subsequent decrement in the fill factor (FF). The FF

depends on the series resistance (RS) and shunt resistance (RSh). The RS is

due to the resistance of the metal contacts, ohmic losses in the front surface

of the cell, impurity concentration and junction depth. Ideally, the RS should be

0Ω. The RSh represents the loss due to surface leakage along the edge of the

cell or due to crystal defects. Ideally, the RSh should be infinite. The value of

RS and RSh are calculated from J-V curves and are given in Table 4.1. RS


124

varies slightly, from 161Ω to 95Ω, while RSh changes drastically, from 759Ω

for CdS10 sample to 100Ω for CdS30 sample. The variation in RSh seems to be

dominant in our case. The consequences of decrease in RSh and FF along

with conversion efficiency (η) are shown in Table 4.1. The highest η is of the

order of 1.42% for CdS30 sample.

Table 4.1:

Sample Jsc

(mA/cm2)

Voc

(mV)

Imax

(mA/cm2)

Vmax

(mV)

RS

(ΩΩΩΩ)

RSh

(ΩΩΩΩ)

Ideality

Factor

FF

(%)

η

(%)

CdS10 1.475 371.96 0.877 293.88 161 759 1.70 47 0.92

CdS20 3.305 375.11 1.440 232.64 98 134 1.94 27 1.20

CdS30 4.179 452.98 1.660 235.16 95 100 2.01 21 1.42

The observed values of JSC in our samples are found to be larger than

other CdS samples with compact planer or porous morphologies [45-47]. The

photocurrent depends upon how efficiently the photogenerated carriers in the

semiconductors are harvested. Photocurrent results from two main collection

mechanisms, separation of the carriers in the space charge field and diffusion

of carriers towards the interface. The hike in JSC in our samples seems to be

due to spongy ball like morphology, which induces following light harvesting

phenomena:

(1) Nanoconduits with interconnected nanowalls increase surface area in

contact with the redox electrolyte.

(2) Effective light absorption by the way of its trapping and scattering in the

nanoconduits. It increases absorption path length of light and thereby

interaction between light and CdS nanocrystallites increases. Hence, the

optical absorption and energy harvesting efficiency of CdS spongy balls are

enhanced (Fig.8).


125

Figure.8 CdS-polysulphide interface formed in the nanoconduits of a spongy

ball. CdS nanowalls, in contact with polysulfide electrolyte, becomes

depleted of electrons (shown as uncompensated donor ions in gray). The

built-in-potential is generated at each CdS nanowalls-polysulfide

electrolyte interface, which enforces an electron- hole pair separation

(shown as dotted lines). Light trapping via multiple scattering-absorption

events in the nanoconduits is shown as progressively dotted arrows.

Highly schematic pathway of photogenerated electrons is also shown.

(3) The nanowalls of 35 nm thickness act essentially as space charge

(depletion) region, which absorb and create electron-hole pair and separate

them effectively due to the built-in potentials at nanowalls-electrolyte interface,

shown by dotted lines in Fig.8.

(4) The interconnected nanowalls serve as direct path ways for photogenrated

electrons and reduce its loss.

hνννν

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

35nm

Electrolyte

(polysulfide)

CdS Nanowall


126

The ideality factor ‘nd’ of prepared CdS films is determined from

following diode equation (eq.4.9) as,

/( 1) (4.9)

qV n kTdI I eo= − − − − − − − − − − −

where, Io is the reverse saturation current, V is forward bias voltage, k

is Boltzmann's constant, T is ambient temperature in Kelvin and nd is an

ideality factor. The ideality factor is determined under forward bias and is

normally found to be in between 1 to 2 depending up on the relation between

diffusion current and recombination current. When diffusion current is more

than recombination current then ideality factor becomes 1 and it becomes 2 in

opposite case. The ideality factor was found to be 1.70, 1.94 and 2.01 for the

sample CdS10, CdS20 and CdS30 respectively.

4.5. Conclusions

The nanocrystalline CdS thin films were successfully deposited by

facile chemical bath deposition method. XRD studies revealed that the

synthesized CdS thin films have cubic structure with improved crystallinity.

SEM shows the spongy balls with nanoconduits like morphology. These

nanoconduits consists densely packed interconnected nanowalls. This

improve light harvesting first because of increase in effective surface area,

which enhances trapping of light and second by intensely scattering light that

is not absorbed, resulting in longer effective path for light to travel through the

nanowalls. The improved crystallinity, as well as, surface area led to

scattering, trapping of light results into enhancement in PEC.


127

References:

[1] K S Ahn, Y Yan, S H Lee, T Deutsch, J Turner, C E Tracy, C L Perkins and

M Al-Jassim J. Electrochem. Soc. 154 (2007) 956.

[2] M Guo, P Diao and S M Cai, Chin. Chem. Lett. 15 (2004) 1113.

[3] A I Inamdar, S H Mujawar, V Ganesan, and P S Patil, Nanotechnology 19

(2008) 325706.

[4] M J Bierman, S Jin, Energy Environ Sci. 2 (2009) 1050.

[5] S Mokrushin, Y Tkachev, Kolloidn 23 (1961) 438.

[6] G Kitaev, A Uritskay, S Mokrushin, Russ. j. Phys. Chem. 39 (1965) 1101.

[7] M Ristov, Sol. Energy Mater. Sol. Cells. 53 (1998) 102.

[8] X Mathew, G W Thompson, V P Singh, J C McClure, S Velumani, N R

Mathews, P J Sebastian, Sol. Energy Mater. Sol. Cells. 76 (2003) 293.

[9] S Kutzmutz, G Lang, K E Heusler, Electrochimica Acta. 47 (2001) 955.

[10] R K Sharma, G Singh, A C Rastogi, Sol. Energy Mater. Sol. Cells. 82 (2004)

201.

[11] K L Chopra, P D Paulson and V Dutta, Prog. Photovolt: Res. Appl. 12 (2004)

69.

[12] M Shalom, S Dor, S Ruhle, L Grinis, and A Zaban, J. Phys. Chem. C13

(2009) 3895.

[13] X Song, Y-S Fu, Y X Jun-Guo, H-Li Song, J S Wang and X-W Du

Semiconductor Sci. Technol. 25 (2010) 045031.

[14] P V Kamat J. Phys. Chem. C 111 (2007) 2834.

[15] A H Zyoud, N Zaatar, I Saadeddin, C Ali, D Park, G Campet, H S Hilal, J.

Hazard. Mater. 173 (2010) 318.

[16] P K M Bandaranayake, P V V Jayaweera, K Tennakone, Sol. Energ. Mat.

Sol. Cells. 76 (2003) 57.

[17] J N Ximello-Quiebras, G Contreras-Puente, J Aguilar-Herna ndez G, A

Santana-Rodriguez, R Arias-Carbajal Sol. Energy Mater. Sol. Cells. 82

(2004) 263.

[18] D P Amalnerkar, K Y Amaguchi, T. Kajita, H Minoura, Solid State Commun.

90 (1994) 3.

[19] H Uda, H Yonezawa, Y Ohtsubo, M Kosaka and H. Sonomura, Sol. Energy

Mater. Sol. Cells. 75 (2003) 219.


128

[20] S Ray, R Banerjee and A K Barua, Jap. J. Appl. Phys. 19 (1980) 1889.

[21] B-Sik Moon, J. H. Lee, H Jung, Thin Solid Films. 299 (2006) 511.

[22] Y J Chang, C L Munsee, G S Herman, J F Wager, P Mugdur, D-H Lee and

C H Chang, Surf. Interface Anal. 37 (2005) 398.

[23] D Redfield, Appl. Phys. Lett. 25 (1974) 647.

[24] E Garnett and P Yang, Nano Lett. 10 (2010) 1082.

[25] S B Rim, S Zhao, S R Scully, M D McGehee, P Peumans, Appl. Phys. Lett.

91 (2007) 243501.

[26] X Sheng, J Zhai, L Jiang, D Zhu, Appl. Phys. A. 96 (2009) 473.

[27] Q Zhang, T P Chou, B Russo, S A Jenekhe and G Cao, Adv. Funct. Mater.

18 (2008) 1654.

[28] T P Chou, Q Zhang, G E Fryxell and G Cao, Adv. Mater. 19 (2007) 2588.

[29] Q Zhang, T P Chou, B Russo, S A Jenekhe and G Cao, Angew. Chem. Int.

Ed. 47 (2008) 2402.

[30] K L Chopra, R C Kainthla, D K Pandya, A P Thakoor, Phys. Thin Films. 12

(1982) 167.

[31] M Froment, D Lincot, Electrochim. Acta. 40 (1995) 1293.

[32] H Moualkia, S Hariech, M S Aida, N Attaf and E L Laifa, J. Phys. D: Appl.

Phys. 42 (2009) 135404.

[33] Y Lida, M Furukawa, T Aoki, T Sakai, Appl. Spectrosc. 52 (1986) 73.

[34] M Li, Z Feng, G Xiong, P Ying, Q Xin, J Li, Phys. Chem. B 105 (2001) 8107.

[35] A Badr, K M AbdEl-Kader, R M Khafagy, J. Appli. Polymer Sci. 92 (2004)

1984.

[36] R C C Leite and S P S Porto, Phys. Rev. Lett. 17 (1966) 10.

[37] F Chen, R J Zhou, L G Yang, N M Wang, H Z Chen, J. Phys. Chem. C 112

(2008) 1001.

[38] Z Q Wang, J F Gong, J H Duan, H B Huang, S G Yang, X N Zhao R Zhang,

W DuY, Appl. Phys. Lett. 89 (2006) 033102.

[39] G Z Shen, C Lee, J. Growth Des. 5 (2005) 1085.

[40] J C Lytle, A Stein, Annual Rev. Nano Res. 1 (20060 1.

[41] Z S Wang, H Kawauchi, T Kashima, H Arakawa, Coord. Chem. Rev. 48

(2004) 1381.

[42] S Nishimura, N Abrams, B A Lewis, L I Halaoui, T E Mallouk, K D Benkstein,


129

J van de Lagemaat, A J Frank, J. Am. Chem. Soc. 125 (2003) 6306.

[43] L I Halaoui, N M Abrams, T E Mallouk, J. Phys. Chem. B. 109 (2005) 6334.

[44] M Karimi, M Rabiee, V Moztarzadeh, M Tahriri and M Bodaghi, Curr. Appli.

Phys. 9 (2009) 1263.

[45] H S Hilal, M A Rania, A Ismail, A El-Hamouz, I S Zyoud, Electrochimica Acta

54 (2009) 3433.

[46] J K Dongre, V Nogriya, M Ramrakhiani, Appli. Surf. Sci. 255 (2009) 6115.

[47] S Tiwari and S Tiwari, Cryst. Res. Technol. 41 (2006) 1 78.

Documents

Synthesis of CdS spongy balls with nanoconduits for ...shodhganga.inflibnet.ac.in/bitstream/10603/4064/10/10_chapter 4.pdf · employing semiconductor-redox systems have been extensively