Nanomaterials in Solar Cells - link.springer.com · Before introducing the added value of nanomaterials in solar cells, a brief comeback should be presented to understand the work

Nanomaterials in Solar Cells

Razika Tala-Ighil*Unité de recherche matériaux, procédés pour l’environnement, URMPE Institute of Electrical & Electronic Engineering,University M’Hamed Bougara, Umbb, Boumerdes, Algeria

Abstract

Reducing cost and improving conversion efficiency are the main tasks in order to make photovoltaicenergy competitive and able to substitute traditional fossil energies.

Nanotechnology seems to be the way by which photovoltaics can be developed, whether in inorganic ororganic solar cells. Wide-bandgap nanostructured materials (nanomaterials) prepared from II–VI andIII–V elements are attracting an increased attention for their potential applications in emerging energy.They can be prepared in different geometric shapes, including nanowires (NWs), nanobelts, nanosprings,nanocombs, and nanopagodas. Variations in the atom arrangements in order to minimize the electrostaticenergy originated from the ionic charge on the polar surface are responsible for a wide range ofnanostructures.

This book chapter will focus on contribution of nanomaterials in solar cell technology advancement.

Keywords

Nanomaterials; Solar cells; Organic; Inorganic; Nanopillars; Nanowires; Nanobelts; Nanorods;Photocarrier collection

Introduction

Solar cells have known a big expansion these last years due to the voluntary move to cleaner energies likephotovoltaics. Table 1 summarizes the chronological evolution of photovoltaic cells with their maincharacteristics.

After solid-state physics has shown its limits by reaching the maximum possible conversion efficiencyfor silicon, CdTe, and CuInSe2, the highest conversion efficiency was obtained for triple-junctioncompound InGaP/GaAs/InGaAs solar cell with 37.9 % [6]. Chemistry seems to be another way bywhich an increase of the solar cell conversion efficiency is possible.

Nanomaterials made by chemical ways present high opportunity in efficiency enhancement byincreasing light trapping and photocarrier collection without additional cost in solar cell fabrication.

The physical and chemical properties change from the bulk material to the nanomaterial. As anexample, the melting point is lowest for the nanomaterial compared to its bulk one. This can be due tothe high surface-to-volume ratio of atoms in a nanoparticle [7].

The main nanomaterial physical property is the large surface-to-volume ratio [6] due to different formscreated; nanowires [8, 9], nanopillars [10, 11], nanocones [12], quantum dots [13].

It has been shown that light trapping is due to the increase of the photon path inside nanostructures[14–16] which enhance the electron–hole pair creation probability.

*Email: [email protected]

Handbook of NanoelectrochemistryDOI 10.1007/978-3-319-15207-3_26-1# Springer International Publishing Switzerland 2015

Page 1 of 18

Quantum dots (QDs) have the particularity to have a size-dependent bandgap [13, 17, 18] so it can beadjusted to fit the maximum solar spectrum.

Classical Solar Cells

Before introducing the added value of nanomaterials in solar cells, a brief comeback should be presentedto understand the work mechanism of solar cells.

A solar cell is an electronic device, a P/N junction in its basic form, which has the ability to convertsunlight into electricity. This phenomenon was discovered by Edmond Becquerel in 1839 and is called thephotovoltaic effect [19].

Not all materials can be solar cell components. Because the main feature should be the capacity toconvert the visible spectrum of the sun into electricity,this can occur only by the creation of electron-holepairs when the material absorbs photons corresponding to an energy greater or equal to its energy gap(Fig. 1).

The air mass (AM) is the level at which the atmosphere reduces the light reaching the Earth’ssurface [21].

AM0: The spectrum outside the atmosphere.

Table 1 The four generations of solar cells and their characteristics

Solar cells evolution Characteristics

First generation: bulk silicon High cost with high efficiency [1]

Second generation: thin film solarcells

Amorphous or polycrystalline silicon, CIGS and CdTe [2, 3]

Third generation Organic solar cells with nano-crystalline films [4]

Fourth generation Combines the low cost/flexibility of polymer thin films with inorganicnanostructures [5]

1.E+06

2000 K

AM1.5

1000 KWien’s displacement law

AMO and 5800 K blackbodyat sun earth distance

1.E+05

1.E+04

1.E+03

1.E+02

1.E+01

1.E+000.0 0.5 1.0 1.5

Wavelength [μm]

2.0 2.5 3.53.0 4.0

Rad

iatio

n [W

/(m

2 μm

]

Fig. 1 Comparison of solar spectra at Sun-Earth distance and blackbody spectra in semi-logarithmic scale reprinted withpermission from Ref. [20]


Page 2 of 18

AM1.5: The used standard solar spectrum for terrestrial solar cells, it corresponds to a solar zenith angleof 48.2�.

From the figure, the blackbody radiation increases from 1,000 to 2,000 K in 200 K steps (small valuesoverlapping with solar spectra are not shown). The blackbody maximum values are given by Wien’sdisplacement law, also shown (black). The AM1.5 solar spectrum (black) shows strong absorption bands,whereas the AM0 spectrum (black) closely matches a 5,800 K blackbody at Sun-Earth distance(gray) [20].

One can see clearly that the blackbody maximum shifts toward higher wavelengths with its temperatureaccording toWien’s displacement law. This law implies that a photovoltaic (PV) cell with a higher-energybandgap corresponds to higher radiator temperature. The bandgap for silicon solar cells is hu = 1.12 eV(which responds up to 1.11 mm) and matches to the maximum of a blackbody at 2,610 K [20, 22]. Themost important part of the solar spectrum ranges in the visible light from 0.38 to 0.76 mm. It reaches itsmaximum at the wavelength of 4 mm [20].

So, the selection criterion of a photovoltaic absorbant is first its energy gap around 1 eV.Manymaterialsfit with this bandgap energy. The most widely used is silicon, with its different forms: monocrystalline ormulticrystalline, gallium arsenide GaAs, cadmium telluride CdTe, copper indium diselenide CIS,Cu2ZnSnS4 (CZTS), and other materials [23–25].

As cited above, a basic solar cell is a P/N junction. A P-type semiconductor has holes in excess while anN-type semiconductor has electrons in excess. There is free carrier migration from one side to the otheruntil reaching equilibrium.

A built-in electric voltage is then created and, in consequence, electron–hole pairs. When the solar cellis connected to an electrical circuit, a current is formed across the PV cell [21] (Fig. 2).

The conversion efficiency (Z) and the fill factor (FF) are calculated according to the equations listedbelow [26]:

Z %ð Þ ¼ Vmax � Jmax

Pin� 100% ¼ Voc � Jsc � FF

Pin� 100%

FF ¼ Vmax � Jmax

Voc � Jsc

where

Jsc: The short-circuit current density (mAcm�2)Voc: The open-circuit voltage (V)Pin : The incident light powerJmax: The current density at the maximum power output in the J-V curves

Light

electronhole

n

E

p

+ + + + + + + + + + + + + + + + + + +

Fig. 2 Basic solar cell structure and effect of light (Reprinted with permission from Ref. [21])


Page 3 of 18

Vmax: The voltage at the maximum power output in the J-V curves

Each parameter has its specific influence on solar cell performance.The fill factor, abbreviated FF, is a parameter which characterizes the nonlinear electrical behavior of

the solar cell. Fill factor is defined as the ratio of the maximum power from the solar cell to the product ofOpen Circuit Voltage Voc and Short-Circuit Current Isc. The typical fill factor for commercial solar cells isusually 0.70 [27].

Classical solar cells require thicker materials to perform good optical absorption but loose carriercollection efficiency due to the higher minority carrier length [28].

Different Forms of Nanomaterials

– Nanowires Different architectures have been proposed by researches to improve the light absorptionand carrier collection [10, 29, 30]As an example, silicon nanowires enhanced the incident solar radiation path length up to a factor of

73 [31].• It has been found that Ag nanowire mesh electrodes show low transparency and low sheet resistance.

They match very well with flexible substrates in organic solar cells. An increase of 19 % in thephotocurrent has been reported [32]

• The nanowires of silver can be deposited by a very low-cost method: simple brush painting, asperformed by J.-W. Lim et al. with a conversion efficiency of 3.231 % [33].

• There are many deposition techniques for nanowire or nanocone arrays. One of the simplest iscolloidal lithography, which is time effective, reproductive, and suitable for large-scale deposition[34]. Another one is the vapor-liquid–solid (VLS) method usually used for a core different from anouter shell (core-shell nanowires) [35].The figure below illustrates the scanning electron microscopy (SEM) images for ZnO nanowires and

nanorods [36] (Fig. 3).– Nanotubes

• Carbon nanotube conductive layers were deposited on n-type silicon to form a Schottky junctionphotovoltaic cell with a conversion efficiency of 1.9 % under AM1.5 illumination. This efficiencyhas been increased to 8.6 % just by chemical charge transfer doping with bis (trifluoramethanesulfanyl) amide [(CF3SO2)2NH] (TFSA) [37].

Fig. 3 Scanning electron micrograph from the different temperature zone showing (a) nanowires and (b) star nanorods(Reprinted with permission from Ref. [36])


Page 4 of 18

The main advantage of this solar cell type is that the graphene’s work function can be varied tooptimize the solar cell efficiency compared to the basic Schottky solar cell with indium tin oxide ITOover silicon (ITO/Si).• Titanium dioxide nanotubes have been employed as transparent photoanodes for dye-sensitized

solar cells. The nanotube shape for TiO2 permits to have unequal electronic properties such as lowcarrier recombination, high electron mobility, and high surface-to-volume ratio [38]. It increases theelectron transport by using direct pathways for the charge transfer [39, 40].

– Nanocones:According to Fig. 4, one can remark that the absorption in a nanocone is greater than the absorption

in a nanowire, which is greater in turn than a thin film. It is obvious that nanomaterials by their specificarchitectures contribute sensibly in conversion efficency increase.Silicon nanowires have shown a short collection length for excited carriers, which enhances

considerably the carrier collection efficiency [14].For classical hydrogenated amorphous silicon [a-Si:H] solar cells, there is an intrinsic problem

which lowers the conversion efficiency. It is due to the high trap amounts that reduce the carrierlifetime.An alternative is proposed by using a nanocone array structure as shown in Fig. 5.

Fig. 4 Absorption of ITO/a-Si:H samples with a-Si:H thin film, nanowire arrays, and nanocone arrays as top layer overdifferent angles of incidence at at wavelength l = 488 nm (Reprinted with permission from Ref. [28] (copyright 2011,Elsevier) and Ref. [12] (copyright 2011, American Chemical Society))

Fig. 5 The schematic structure for a nanocone solar cell. Enlarged part of the a-SiH-nanocone structure describes thephotogeneration and transport mechanism (Reprinted with permission from Ref. [41])


Page 5 of 18

With carrier collection enhancement, an efficiency increase has been observed from 1.43 % to1.77 % and so an enhancement of 24 % [41].

– Nanopillars: Nanopillar photovoltaics has many features that confer to it the capacity to replaceclassical photovoltaics due to its low cost. They can be listed below:1. Growth of cristallized materials without using expensive techniques2. Increase of carrier collection efficiency3. Reduction of optical lossesThe fabrication process of nanopillars is well illustrated in Fig. 5. There are four main steps:

electropolishing, first anodization, wet etching, and finally the second anodization step [42] (Fig. 6).– Nanobelts

• Transparent graphene, i.e., carbon nanotube (CNT), layers have been used to cover CdSe nanobeltsalong certain positions. Really interesting solar cells based on Schottky junction have been made

graphiteelectrode

chillerbath

(i) Electropolishing

EtOH/HCIO4

oxalicacid

oxalicacid

H3PO4

(i) (ii) (iii) (iv)

Bare Al foil

Al

Polished Al foil

Al2O3

IrregularAAO pores

RegularAl bowls

RegularAAO pores

(ii) 1st Anodization (iii) Etching (iv) 2nd Anodization

1

2

3

3

4

4

5

6

a b

c

d

e

Al foil

Fig. 6 R2R Al texturing system: (a) optical image of the R2R system used for Al texturization. The important components ofthe system are highlighted as (1) Al feeding roll, (2) electrical contact to the Al foil, (3) reaction chamber, (4) rinse bath, (5)capstan roll, and (6) rewinding roll. (b) Zoomed-in optical image of the reaction chamber, and (c) The rinse bath, respectively(d) Schematic diagrams of the process, and (e) The resulting surface structure after (i) electropolishing, (ii) first anodization,(iii) AAO wet etching and (iv) second anodization steps used for the fabrication of various surface textures (Reprinted withpermission from Ref. [42] (copyright 2011, Elsevier) and Ref. [43] (copyright 2011, American Chemical Society))


Page 6 of 18

with this method by using different configurations and several connections from single or multipleassembled nanobelts [44].The above solar cell has been fabricated by following three steps: the first one is the CdSe nanobelt

deposition, then the graphene transfer, and finally the Ag paste contact formation.The particularity of this solar cell is its low-cost manufacturing method based essentially on the

chemical vapor deposition (CVD) process for both CdSe nanobelts and graphene films in addition tobeing a flexible thin-film photovoltaic cell [45].A conversion efficiency of 0.1 % has been reached with an open-circuit voltage of 0.5 Vand a short-

circuit current density Jsc of 0.94 mA/cm2 [44]. The cited photovoltaic structure is shown in Fig. 7:One can remark that the small value of the conversion efficiency (0.1 %) is affected essentially by the

weak value of the fill factor (FF) (less than 23.7 %) [44]. An improvement of this parameter is requiredto increase sensibly the conversion efficiency and to assess the position of this solar cell type as analternative to the classical ones.

– NanopagodasAligned ZnO nanopagoda arrays have been succesfully carried out by Chang Yu-Cheng

et al. [46]. They have very interesting properties in field emission devices and will permit tomanufacture promising devices, especially dye-sensitized solar cells.

Fig. 7 Graphene – CdSe nanobelt schottky junction solar cells: illustration of a single layer graphene covered on the topsurface of a CdSe nanobelt. The overlapped area forms the junction that is responsible for charge separation (Reprinted withpermission from Ref. [44])

Fig. 8 Scanning electron micrograph of comb-like structures (Reprinted with permission from Ref. [36])


Page 7 of 18

– NanocombsThe nanocomb-shaped nanomaterials are represented in Fig. 8.

– Nanorods• Conjugated polymer donor and a ZnO acceptor have been used for elaboration of hybrid polymer

solar cells. For this purpose, ZnO nanorods were grown on an indium tin oxide–coated glass from amixture containing Zn+2 by using a hydrothermal method [47].The ZnO nanorods which contain the filtered solution poly [1-methoxy-4-(2-ethylhexyloxy-2,5-

phenylenevinylene)] form the active layer for the hybrid bulk heterojunction solar cells. An efficiencyof only 0.045 % was obtained, which reveals that work should be done to reduce the high interiorresistance of the PV cell [47].Figure 9 illustrates the scanning electron microscopy images for different Zn+2 concentrations:

0.0125, 0.025, 0.05, and 0.1 mole. The ZnO nanorod diameter becomes bigger with increasing Zn+2

concentration [47].It has been found that the electron mobility is 10�1 to 10�3 cm2 V�1 s�1 for nano zinc oxide and

100 cm2 V�1 s�1 for bulk zinc oxide. There is a considerable difference which explains the higherquality of nano ZnO compared to bulk ZnO [47].The 0.3 eVenergy level difference of zinc oxide with polymer donors leads to the efficient separation

of excitons into free carriers [48, 49].

Nanomaterials in Inorganic Solar Cells

– Silicon: Increase in silicon solar cell performance can be obtained by improving silver screen-printedcontact. This can be done by introducing silver nanoparticles in the paste to increase contact compact-ness and consequently the fill factor and the conversion efficiency Z.

Fig. 9 SEM top-view image of ZnO nanorods under different Zn+2 concentrations: (a) 0.0125; (b) 0.025; (c) 0.05; and (d)0.1 M (Reprinted with permission from Ref. [47])


Page 8 of 18

Silicon can be also used as nanowires in solar cells. Their diameters vary from 200 nm to 1.5 mm. Ithas been found that the minority carrier diffusion length is around 2 mm, the minimum carrier lifetime is15 ns, while the maximum surface recombination velocity is approximately 1,350 cm s�1 [50].These values are really different for silicon bulk material: the diffusion length is around 200 mm, the

minimum carrier lifetime 30 ms, and finally the surface recombination velocity 8,600 cm/s [51].The effect of nanomaterials in improving solar cell efficiency seems to be obvious when the previous

data are compared. The recombination velocity is reduced with the nanomaterial structure, whichmeans that photon collection is increased (Fig. 10).

– CuInSe2 Copper indium diselenide (CIS) thin layers represent another type of absorbant widely usedin photovoltaics due to the fact that their energy gap matches perfectly the maximum solar spectra [53].This type of material has the advantage compared to silicon of quantity of matter: the CIS is

deposited as thin films with approximately 1 mm thickness while for silicon thick substrates of around300 mm are required.A second CIS advantage comes from the fact that to have type n or p semiconductor, there is no need

of doping; just a small deviation of stoichiometry is necessary.The classical CIS has generally the following structure: Mo/CuInSe2/CdS/ZnO solar cell

Mo is molybdenum and represents the rear contact.CuInSe2 is the CIS pn junction CIS(p)/CIS(n).CdS is the buffer layerZnO is the window layerMany techniques have been used to deposit CIS layers: coevaporation and sputtering [54–56]A conversion efficiency of 20.1 % has been reported for CIS films deposited by coevaporation [55]The CISmorphology can be tuned just by changing the amount of strong and weak surfactants which

passivate the surface. For example CIS nanowires can be obtained by using weakly bindingdioctylphosphine oxide (DOPO), an impurity in trioctylphosphine oxide (TOPO) [57].

Band gap for spherical CIS nanoparticles can be adjusted according to the nanoparticles radius. While for CIS nanorodsinfluence directly the energy gap, the diameter of the nanorods influence directly [57].

For p-type CuIn1�xGaxSe2 (CIGS) layers introduced in solar cells, electron mobilities vary from0.02 to 0.05 cm2/Vs. These values are less than those for n-type CIGSmaterials, which sweep from 2 to1,100 cm2/Vs [58].

Fig. 10 FESEM micrograph of the as -prepared silver nanoparticles prepared by solvothermal process (Reprinted withpermission from Ref. [52])


Page 9 of 18

An efficiency of 15 % for classical CIGS solar cells has been reported [58].– CdTe Cadmium telluride (CdTe) is one of the absorbant PV materials with its bandgap of 1.45 eV. It is

used also combined to cadmium sulfide (CdS).The solar cell structure ITO/CdTe/CdS/CNTs acts as front electrode/p-type semiconductor/n-type

semiconductor/rear contact.where CNTs: carbon nanotubesITO: indium tin oxideA conversion efficiency from 3.5 % at ortogonal azimuthal angle to 7 % at 45� solar incidence [34].

– CdSCadmium sulfide (CdS) enters in the fabrication of the solar cells based on fluorine-doped tin oxide

(FTO)/Au/TiO2/CdS photoanode and polysulfide electrolyte. Gold nanoparticles have been used as aninterfacial layer between FTO and TiO2. Conversion efficiency increases from 0.86 % to 1.62 % for thestructures FTO/Au/TiO2/CdS and FTO/TiO2/CdS respectively. So there is an enhancement of 88% duebasically to the Au nanoparticle incorporation [31].Successive ionic layer adsorption and reaction (SILAR) techniques have been used for CdS

deposition onto TiO2 layers [59].– CdSe

• The combination CdTe/CdSe core/shell structures have the particularity to emit in the near-infraredregion, which doesn’t exist for CdTe or CdTe nanoparticles taken apart [60].

The success of the structure core/shell depends directly on the lowest lattice mismatch betweenthe used materials [61].Polymeric solar cells with CdTe quantum dots (QDs) with single-wall carbon nanotubes (SWNTs)

incorporated into a poly(3-octylthiophene)-(P3OT) composite have shown good exciton dissociationand carrier transport. An open-circuit voltage Voc = 0.75 V and short-circuit current densityJsc=0.16 mA/cm2 have been obtained [62].

Nanomaterials in Organic Solar Cells

Organic solar cells have gained attention these last years. Key phenomena in PV cell manufacturing wereconsequently mastered like exciton generation effect, light trapping, and one-dimensional material forSchottky barrier arrays [63].

Organic solar cells, also called photoelectrochemical solar cells, are composed of photoactive electrode(semiconductor) and counter electrode (metal or semiconductor) immersed, both of them, in an electrolytewhich contains redox couples. Electron/hole pairs are created when light with energy greater than those ofthe semiconductor is absorbed [64] (Fig. 11).

Pt

APt cathode

P3HT:PCBM PV Layer

PEDOT:PSSFTO

Glass substrate

V

P3HT and PCBM

Dye/tiO2/PEDOT:PSS

Anode buffer layer

FTO

glass

Fig. 11 Schematic diagram of FTO/TiO2/dye/PEDOT:PSS/P3HT:PCBM (PSCs-1) and FTO/PEDOT:PSS/P3HT:PCBM(PSCs-2) heterojunction solar cells (Reprinted with permission from Ref. [65])


Page 10 of 18

Photoanodes for Dye-Sensitized Solar Cells

– TiO2

The corresponding solar cell performances are represented in Tables 2 and 3 [65].TiO2 nanomaterials can also be prepared by following a novel method, by combining dealloying

process with chemical synthesis. A hierarchical nanostructure was obtained with a thickness ofapproximately 10 mm. It has the shape of nanoflower arrays and nanorods [66].The nanoflower is composed of many nanopetals of 100–200 nm in diameter [66].For titanium dioxide TiO2, a new process called low-temperature solid-state dye-sensitized solar cell

(LT-SDSC) has been carried out. As its name denotes, everything is obtained at low temperatures,which reduces directly the energy cost and yields cheaper solar cells [67].It consists in a mesoporous TiO2 (mp-TiO2) layer realized from a binder-free nanoparticle TiO2 paste

at room temperature. A conversion efficiency of 1.30 % was found for a photovoltaic cell withLT-SDSC 0.9 mm mp-TiO2 and 20 nm ALD-TiO2 [67].

– ITO: According to reference [68], an organic solar cell (OSC) has been prepared by using electro-chemistry method.The structure of this organic solar cell is presented in Fig. 12:

The bilayer heterojunction (OSC) had followed a two-step solution-based method: firstly electrode-positing polythiophene (PTh) and secondly a spin-coating chloroform solution of [6, 6]- phenylC61-butyric acid methyl ester (PCBM) onto the PTh layer [68].

The PTh layer plays the role of a donor material due to its high hole mobility [68].The conversion efficiency of this structure is around 0.1 % [68].

– ZnOHybrid solar cells based on the structure FTO/TiO2/N719/P3HT:PCBM/Au have been fabricated

[69] withFTO: fluorine-doped tin oxide SnO2:FTiO2: titanium dioxide shaped as nanotube arraysN719: Ruthenium (II) dyeP3HT: poly (3-hexyl-thiophene)PCBM: [6, 6]-phynyl-C61-butyric acid methyl ester (PCBM)

Table 2 Photoelectric performances for PSC-1 (Reprinted with permission from Ref. [65])

P3HT:PCBM (2:1) Voc (V) Jsc (mAcm�2) FF Z (%)

Barrier 0.82 3.63 0.68 2.04

Atm. annealed 0.83 3.96 0.67 2.19

Vacuum annealed 0.83 4.30 0.67 2.37

Table 3 Photoelectric performances for PSC-2 (Reprinted with permission from Ref. [65])

P3HT:PCBM (2:1) Voc (V) Jsc (mAcm�2) FF Z (%)

Barrier 0.80 2.83 0.65 1.48

Atm. annealed 0.78 3.27 0.62 1.58

Vacuum annealed 0.80 3.59 0.66 1.90


Page 11 of 18

TiO2 nanotube arrays have been deposited on FTO by using a liquid-phase deposition method withZnO template while the zinc oxide nanorods have been grown according to the method detailed in thereferences [70–73].The hydrothermal process for ZnO nanorods can be summarized as follows:Zn(CH3COO)2 was added to water with stirring; after 10 min, citric acid was added to the previous

mixture. After that, these solutions were sealed in stainless autoclaves at temperatures 120 �C, 160 �C,and 200 �C during 20 h. Awhite product was obtained and dried at 60 �C [71].A conversion efficiency of 0.656 % was obtained [69].

Nanomaterial-Based Solar Cell Performance

• Anodic titanium oxide (ATO) nanotube–based dye-sensitized solar cells have shown a conversionefficiency of 2.9 %, 3.9 % and a fill factor of 0.51, 0.65 with and without bottom reductive dopingtreatment respectively [74].

I(V) characteristic for CdS NW core and Cu2S shell [75] (Figs. 13 and 14).Table 4 shows the organic solar cell performance [68]:

• Concerning the nanocone silicon solar cells, their performance is reported in Table 5 [41].Thus, there is an efficiency increase when the nanocone architecture is adopted. The effect of the

nanomaterial shape is confirmed.• The characteristic of the structure FTO/TiO2/CdS with and without gold nanoparticles is shown in

Table 6.• SWNTs, in other words “the semiconducting single-walled carbon nanotubes”: by using this material,

Zhang et al. have achieved a solar cell with a conversion efficiency of 12.6 % [76].• For dye-sensitized solar cells (DSSCs) based on TiO2 nanocrystalline electrodes, Andréa de Morais

et al. have improved their efficiency by introducing acid-treated multiwall carbon nanotubes(MWCNT-COOH). A conversion efficiency of 3.05 % was obtained for DSSC based on MWCNT-TiO2 and 2.36 % for DSSC based on TiO2 [77].

LiF/Al line profile

PTh surface

PCBM

PTh

ITO

glass

0 1 2 3 4 50

1

0

13

nmμm

μm

Fig. 12 The schematic structure of ITO/PTh/PCBM/LiF/Al organic solar cell (left) and AFM image (bottom right) ofPTh/PCBM interface with profile line (top right) (Reprinted with permission from Ref. [68])


Page 12 of 18

Conclusion

Solar cell performance is the perpetual challenge for researchers to make photovoltaic energy widely usedin our daily life.

Nano-electrochemistry seems to be a non-negligible alternative for widely used, high-performance, andlow-cost solar cell fabrication by employing processes based essentially on chemistry.

It is due basically on the fact that these processes are carried out at low temperatures or at ambienttemperature, which reduces sensibly the energy bill for photovoltaic cell manufacturing.

1.0l TOZnOMEH-PPVPEDOT: PSSAl

ISC = 0.40 mA•cm–2

VOC= 0.43 VFF = 0.265η= 0.045 %

0.8

0.6

0.4

0.2

0.0

–0.2

–0.4

–0.6

–0.2 0.0 0.2

Voltage (V)

Cur

rent

den

sity

(m

A•c

m–2

)

0.4 0.6 0.8

Fig. 13 I(V) characteristics of the MEH-PR/ZnO nanorod hybrid polymer solar cell illumination with a 100 mW/cm2 lightdensity (Reprinted with permission from Ref. [47])

35

30

25Paste ID

A 622

618

34.6 74.8 16.1

15.472.534.3

Voc(mV)

Jsc(mA/cm2)

FF(%)

Eff(%)

B

20

15

J SC (

mA

/cm

2 )

10

5

00 100 200 300

Voltage(mV)

400 500 600

Fig. 14 I(V) performances of crystalline silicon solar cells based on different silver paste under AM1.5 (1,000 W/m2)(Reprinted with permission from Ref. [52])


Page 13 of 18

Despite the fact that the conversion efficiency obtained by conventional solar cells is relatively highcompared to nanomaterial-based solar cells, they remain more attractive because of their low manufactur-ing cost and potential wide implementation in people’s everyday life.

This shift to nano-electrochemistry tends to overcome the limits encountered by solid-state physics.High opportunities to increase light trapping and photocarrier collection have been reached.

Different and interesting architectures were carried out like nanowires, nanorods, nanosprings,nanocones, nanotubes, nanopillars, nanobelts, nanopagodas, nanoflowers, nanopetals, and others.

But the real improvement is observed in inorganic solar cells rather than the organic ones.Organic solar cells are promising next-generation solar cells but cannot be competitive with the

inorganic ones. Their actual conversion efficiency is too small to provide electricity and to have large-scale application. Efforts should be made to make this possible.

References

1. Chiappafreddo P, Gagliardi A (2010) The photovoltaic market facing the challenge of organic solarcells: economic and technical perspectives. Transit Stud Rev 17:346–355. doi:10.1007/s11300-010-0148-0

2. Akl AA, Afify HH (2008) Growth, microstructure, optical and electrical properties of sprayedCuInSe2 polycrystalline films. Mater Res Bull 43:1539–1548

3. Tauc J (2005) Optical properties of amorphous semiconductors and solar cells. In: Yu PY, CardonaM (eds) Fundamentals of semiconductors: physics and materials properties. Springer, Berlin/Heidel-berg, pp 566–568. ISBN 3-540-25470-6

4. Wanzhu Cai, Xiong Gong, Yong Cao (2010) Polymer solar cells: recent development and possibleroutes for improvement in the performance. Sol Energy Mater Sol Cells 94:114–127

Table 4 The performances of single-layer (PTh) and bilayer (PTh/PCBM) solar cell devices under illumination of AM1.5(100 mWcm�2) (Reprinted with permission from reference [68])

Active layer Jsc (mAcm�2) Voc (V) FF PCE (%)

PTh 0.02 0.8 0.26 0.004

PTh/PCBM 0.4 0.6 0.42 0.1

Table 5 The detailed photovoltaic properties of a-Si:H nanocone solar cell, PCE power conversion efficiency, Jsc short circuitcurrent density, Rsh shunt resistance, Voc open circuit voltage, Rs series resistance (Reprinted with permission from Ref. [41])

Type PCE (%) Jsc (mA/cm2)/Rsh(O-cm2) Fill factor (%) Voc (V)/Rs (O-cm2)

PI/N 1.43 5.0/624 36.4 0.78/176

P/I(nanocone)/N 1.77 5.7/572 38.5 0.80/160

P/I(nanocone)/N (H2 Plasma) 2.0 5.8/800 41.4 0.83/62

P/I(nanocone)/N (H2 Plasma + 10 nm) 2.2 5.9/847 44.3 0.83/61

Table 6 Photovoltaic parameters of FTO/TiO2/CdS and FTO/Au/TiO2/CdS cells (Reprinted with permission from Ref. [59])

Electrode Voc (V) Isc (mA/cm2) FF Z (%)

FTO/Au/TiO2/CdS 0.56 7.11 0.41 1.62

FTO/TiO2/CdS 0.47 5.72 0.38 0.82


Page 14 of 18

5. Imalka Jayawardena KDG, Rozanski LJ, Mills CA, Beliatis MJ, Aamina Nismy N, Silva SRP(2013) Inorganics-in-Organics: Recent developments and outlook for 4G polymer solar cells.Nanoscale 5:8411–8427. doi:10.1039/C3NR02733C

6. http://sharp-world.com/Corporate/news/130424.html. 24 Apr 20137. Goldstein AN, Echer CM, Alivisatos AP (1992) Melting in semiconductor nanocrystals. Science

256(5062):1425–14278. Garnett EC, Burthraw D (2005) Cost effectiveness of renewable electricity policies. Energy Econ

27:8739. Yuhas BD, Yang P (2009) Nanowire-based all-oxide solar cells. J Am Chem Soc 131:3756

10. Fan ZY, Razavi H, Do JW,Moriwaki A, Ergen O, Chuch YL, Leu PW, Ho JC, Takahashi T, ReichertzLA, Neale S, Yu K, Wu M, Ager JM, Javey A (2009) Three-dimensional nanopillar-array photovol-taics on low-cost and flexible substrates. Nat Mater 8:3756

11. Cho K, Rurbrush DJ, Ergen O, Javey A (2011) Molecular monolayers for conformal, nanoscaledoping of InP nanopillar photovoltaics. Appl Phys Lett 98:203101

12. Zhu J, Yu ZF, Burkhard GF, Hsu CM, Connor SH, Xu YQ, Wang Q, Mc Gehee M, Fan SH, CuiY (2009) Optical absorption enhancement in amorphous silicon nanowire and nanocone arrays. NanoLett 9:279

13. Peng ZA, Peng X (2001) Formation of high quality CdTe, CdSe, and CdN nanocrystals using CdO asprecursor. J Am Chem Soc 123:183

14. Hu L, Chen G (2007) Analysis of optical absorption in silicon nanowire arrays for photovoltaicapplications. Nano Lett 7(11):3249

15. Han SE, Chen G (2010) Optical absorption enhancement in silicon nanohole arrays for solarphotovoltaics. Nano Lett 10:1012

16. Han SE, Chen G (2010) Toward the Lanbertian limit of light trapping in thin nanostructured siliconsolar cells. Nano Lett 10:4692

17. Peng X, Wickham J, Alivisatos AP (1998) Kinetics of II-VI and III-V colloidal semiconductornanocrystal growth: ‘focusing’ of size distributions. J Am Chem Soc 120:5343

18. Rogach AL, Talapin DV, Shevchenko EV, Kowowski A, Haase M, Weller H (2012) Organization ofmatter on different size scales: monodisperse nanocrystals and their superstructures. Adv FunctMater12:653

19. Sze SM, Kwok KNg (2007) Physics of semiconductor devices. Wiley, USA20. Bauer T (2011) Thermophotovoltaic basic principles and critical aspects of system design, Green

energy and technology. Springer, Berlin/Heidelberg. doi:10.1007/978-3-642-19965-3_521. Pode R, Diouf B (2011) Solar lighting, Green energy and technology. Springer, Berlin/Heidelberg.

doi:10.1007/978-1-4471-2134-3_222. Modest MM (1993) Radiative heat transfer. Mc Graw Hill, New York23. Compaan AD (2006) Photovoltaics: clean power for the 21st century. Sol Energy Mater Sol Cells

90:2170–218024. Xin Zhang, Xuezhao Shi, Weichun Ye, Chuanli Ma, Chunming Wang (2009) Electrochemical

deposition of quartenary Cu2ZnSnS4 thin films as potential solar cell material. Appl Phys A MaterSci Process 94:381–386. doi:10.1007/00339-008-4815-5

25. Takashi Jimbo, Tetsuo Soga, Yasuhiko Hayashi (2005) Development of new materials for solar cellsin Nagoya Institute of Technology. Sci Technol Adv Mater 6:27–33

26. Nazeerudin MK, Péchy P, Renouard T, Zakeeruddin SM, Humphry-Baker R, Liska P, Cevey L,Costa E, Shklover V, Spiccia L, Deacon G, Bignozzi CA, Grätzel M (2001) Engineering of efficientpanchromatic sensitizers for nanocrystalline TiO2-based solar cells. J Am Chem Soc 123:1613


Page 15 of 18

http://sharp-world.com/Corporate/news/130424.html

27. Nehaoua N, Chergui Y, Mekki DE (2011) A new model for extracting the physical parameters fromI-V curves of organic and inorganic solar cells. In: Kosyachenko LA (ed) Solar cells – siliconwafer – based technologies. In-Tech Croatia. doi:10.5772/24854. ISBN 978-953-307-747-5

28. Rui Yu, Qingfeng Lin, Siu-Fung Leung, Zhiyong Fan (2012) Nanomaterials and nanostructures forefficient light absorption and photovoltaics. Nano Energy 1:57–72

29. Kelzenberg MD, Putnam MC, Warren EL, Spurgeon JM, Briggs RM, Lewis NS, Atwater HA(2010) Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications.Nat Mater 9:239

30. Spurgeon JM, Atwater HA, Lewis NS (2008) A comparison between the behavior of nanorod arrayand planar Cd(Se, Te) photoelectrodes. J Phys Chem C 112:6186

31. Garnett E, Yang P (2010) Light trapping in silicon nanowire solar cells. Nano Lett 10:108232. Lee JY, Connor ST, Cui Y, Peumans P (2008) Solution processed metal nanowire mesh transparent

electrodes. Nano Lett 8:689–69233. Jong-Wook Lim, Da-Young Cho, Jihoon-Kim, Seok-In Na, Han-Ki Kim (2012) Simple brush-

painting of flexible and transparent Ag nanowire network electrodes. Sol Energy Mater Sol Cells107:348–354

34. Mia Yu, Yun-Ze Long, Bin Sun, Zhiyong Fan (2012) Recent advances in solar cells based onone-dimensional nanostructure arrays. Nanoscale 4:2783

35. Yu PY, Cardona M (2010) Fundamentals of semiconductors: physics and materials properties.Springer, Berlin. ISBN 978-3-642-00710-1

36. Srivastava ON, Srivastava A, Dash D, Singh DP, Yadav RM, Mishra PR, Singh J (2005) Synthesis,characterizations and applications of some nanomaterials (TiO2 and SiC nanostructured films,organized CNT structures, ZnO structures and CNT-blood platelet clusters). Pramana J Phys64(4):581–592

37. Miao X, Tongay S, Petterson MK, Berke K, Rinzler AG, Appleton BR, Hebard AF (2012) Highefficiency graphene solar cells by chemical doping. Nano Lett 12:2745, ArXiv: 1209.0432v1 [cond-mat.mtrl-sci]

38. Lamberti A, Sacco A, Bianco S, Manfredi D, Armandi M, Quaglio M, Tresso E, Pirri CF (2013) Aneasy approach for the fabrication of TiO2 nanotube based transparent photoanodes for dye sensitizedsolar cells. Sol Energy 95:90–98

39. Baker DR, Kamat PV (2009) Photosensitization of TiO2 nanostructure with CdS quantum dots:particulate versus tubular support architectures. Adv Funct Mater 19:805–811

40. Paulose M, Shankar M, Varghese OK, Mor GK, Grimes CA (2006) Application of highly orderedTiO2 nanotube arrays in heterojunction dye sensitized solar cells. J Phys D Appl Phys 39:2498–2503

41. Thiyagu S, Pei Z, Jhong M-S (2012) Amorphous silicon nanocone array solar cell. Nanoscale ResLett 7:172

42. Kapadia R, Fan Z, Takie K, Javey A (2012) Nanopillar photovoltaics: materials, processes anddevices. Nano Energy 1(1):132–134

43. Lee MH, Lim N, Ruebusch DJ, Jamshidi A, Kapadia R, Lee R, Seok TJ, Takei K, Cho KY, Fan Z,Jang H, Wu M, Cho G, Javey A (2011) Roll to roll anodization and etching of aluminum foils forhigh-throughput surface nanotexturing. Nano Lett 11:3425

44. Luhui Zhang, Lili Fan, Zhen Li, Enzheng Shi, Xinming Li, Hongbian Li, Chunyan Ji, Yi Jia, JinquanWei, Kunlin Wang, Hongwei Zhu, Dehai Wu, Anyuan Cao (2011) Graphene- CdSe nanobelt solarcells with tunable configurations. Nano Res 4(9):891–900. doi:10.1007/s12274-011-0145-6

45. Zhang LH, Jia Y, Wang SS, Li Z, Ji CY, Wei JQ, Zhu HW, Wang KL, Wu DH, Shi EZ, Fang Y, CaoAY (2010) Carbon nanotube and CdSe nanobelt Schottky junction solar cells. Nano Lett10:3583–3589


Page 16 of 18

46. Chang Yu-Cheng, Yang Wei-Cheich, Chang Che-Ming, Hsu Che-Ming, Hsu Po-Chun, ChenLin-Juann (2009) Controlled growth of ZnO nanopagoda arrays with varied lamination and apexangle. Cryst Growth Des 9(7):3161–6167

47. Zhang LN, Yan LT, Ai XD, Li TW, Dai CA (2012) Preparation of a hybrid polymer solar cells basedon MEH-PPV/ZnO nanorods. J Mater Sci Mater Electron. doi:10.1007/s10854-012-0728-3

48. Zhang Q, Dandeneau CS, Zhou X, Cao G (2009) ZnO nanostructures for dye sensitized solar cells.Adv Mater 21:4087

49. Thorat JH, Kanade KG, Nikam LK, Chaudhari PD, Kale BB (2011) Nanostructured ZnO hexagonsand optical properties. J Mater Sci Mater Electron 22:394

50. Kelzenberg MD, Turner-Evans DB, Kayes BM, Filler MA, Putnam MC, Lewis NS, Atwater HA(2008) Photovoltaic measurements in single nanowire silicon solar cells. Nano Lett 8(2):710–714

51. Tala-Ighil R (2013) Simulated multi-crystalline silicon solar cells with aluminum back surface field.Mater Sci Indian J 9(7):277–281

52. Quande Che, Hongxing Yang, Lin Lu, Yuanhoo Wang (2012) Nanoparticles-aided silver frontcontact paste for crystalline silicon solar cells. J Mater Sci Mater Electron. doi:10.1007/s10854-012-0941-0

53. Dongwook Lee, Yougwoo Choi, Kijing Yong (2010) Morphology and crystal phase evolution ofdoctor-blade coated CuInSe2 thin films. J Cryst Growth 312:3665–3669

54. Ludwig C, Gruhn T, Felser C (2010) Indium – gallium segregation in CuInxGa1-xSe2: an ab initio-based Monte Carlo study. Phys Rev Lett 105:025702

55. Klenk R, Klaer J, Scheer R, Lux-Steiner MCh, Luck I, Meyer N, R€uhle U (2005) Solar cells based onCuInS2- an overview. Thin Solid Films 480:509

56. Lux Steiner MCh, Ennaoui A, Fisher Ch-H, Jäger-Waldau A, Klaer J, Klerk R, Könenkamp R,Matthes Th, Scheer R, Siebentritt S, Weidinger A (2000) Processes for chalcopyrite-based solar cells.Thin Solid Films 361:533–539

57. Wark SE (2011) Simple chemical routes for changing composition or morphology in metal chalco-genide nanomaterials. Dissertation Doctor in Phylosophy, Texas A&M University, May 2011

58. Dinca SA, Schiff EA, Shafarman WN, Egaas B, Noufi R (2012) Electron drift-mobility measure-ments in polycrystalline CuIn1-xGaxSe2 solar cells. Appl Phys Lett 100:103901. doi:10.1063/1.3692165

59. Guang Zhu, Fengfang Su, Tian Lv, Likun Pan, Zhuo Sun (2010) Au nanoparticles as interfacial layerfor CdS quantum dot-sensitized solar cells. Nanoscale Res Lett 5:1749–1754. doi:10.1007/s11671-010-9705-z

60. Kim S, Fisher B, Eisler HJ, Bawendi M (2003) Type II quantum dots: CdTe/CdSe (core/shell) andCdSe/ZnTe (core/shell) heterostructures. J Am Chem Soc 125(38):11466–11467

61. Milliron DJ, Hughes SM, Cui Y, Manna L, Li JB, Wang LW, Alivisados AP, Colloidal AP(2004) Nanocrystal heterostructures with linear and branched topology. Nature 430(6996):190–195

62. Landi BJ, Castro SL, Ruf HJ, Evans CM, Bailey SG, Raffaelle RP (2005) CdSe quantum – singlewall carbon nanotube complexes for polymeric solar cells. Sol Energy Mater Sol Cells 87:733–746

63. Yafei Zhang, Huijuan Geng, Zhihua Zhou, Jiang Wu, Zhiming Wang, Yaozhong Zhang, Zhongli Li,Liying Zhang, Zhi Yang, HueyLiang Hwang (2012) Development of inorganic solar cells bynanotechnology. Nano Micro Lett 4(2):124–134

64. Wei D (2010) Dye sensitized solar cells. Int J Mol Sci 11:1103–1113. ISSN 1422-006765. Yan Li, Gentian Yue, Xiaoxu Chen, Benlin He, Lei Chu, Haiyan Chen, Jihuai Wu, Qunwei Tang

(2013) Application of poly(3,4-ethylenedioxythiophene): polystyrenesulfonate in polymerheterojunction solar cell. J Mater Sci 48:3528–3534. doi:10.1007/s10853-013-7147-6


Page 17 of 18

66. Shengli Zhu, Guoquiang Xie, Xian Jin Yang, Zhenduo Cui (2013) A thick hierarchical rutile TiO2

nanomaterial with multilayered structure. Mater Res Bull 48:1961–196667. Jiang CY, KohWL, Leung MY, Chian SY, Wu JS, Zhang J (2012) Low temperature processing solid

state dye sensitized solar cells. Appl Phys Lett 100:11390168. Weili Yu, Bin Xu, Qingfeng Dong, Yinhua Zhou, Junhu Zhang, Wenjing Tian, Bai Yang (2010)

A two-step method combining electrodepositing and spin-coating for solar cell processing. J SolidState Electrochem 14:1051–1056. doi:10.1007/s10008-009-0919-x

69. Rattanavoravipa T, Sagawa T, Yoshikawa S (2008) Photovoltaic performance of hybrid solar cellwith TiO2 nanotubes arrays fabricated through liquid deposition using ZnO template. Sol EnergyMater Sol Cells 92:1445–1449

70. Yu K, Zhang Y, Luo L, Ouyang S, Geng H, Zhu Z (2005) Synthesis of ZnO nanostructures on CuOcatalyzed porous silicon substrate. Mater Lett 59:3525

71. Zhang H, Yang D, Li S, Ma X, Ji Y, Xu J, Que D (2005) Controllable growth of ZnO nanostructuresby citric acid assisted hydrothermal process. Mater Lett 59:1696

72. Peterson RB, Fields CI, Gredd BA (2004) Epitaxial chemical deposition of ZnO nanocolumns fromNaOH solutions. Langmuir 20:5114

73. Lee Y-J, Sounart TL, Scrymgeour DA, Voigt JA, Hsu JWP (2007) Control of ZnO nanorod arrayalignment synthesized via seeded solution growth. J Cryst Growth 304:80

74. Li D, Chang P, Chien C, Lu JG (2010) Applications of tunable TiO2 nanotubes as nanotemplate andphotovoltaic device. Chem Mater 22:5707

75. Kelzenberg MD, Turner Evans DB, Putnam MC, Boettcher SW, Briggs RM, Baek JY, Lewis NS,Atwater HA (2011) High performance Si microwire photovoltaics. Energy Environ Sci 4:866

76. Chen C, Lu Y, Kong ES, Zhang Y, Lee ST (2008) Nanowelded carbon nanotube based solarmicrocells. Small 4:1313

77. de Morais A, Loiola LMD, Beneditti JE, Gonçalves AS, Avellaneda CAO, Clerici JH, Cotta MA,Nogueira AF (2013) Enhancing in the performance of functionalized multi-walled carbon nanotubesinto TiO2 films: the role of MWCNT addition. J Photochem Photobiol A Chem 251:78–84


Page 18 of 18

Nanomaterials in Solar Cells - link.springer.com · Before introducing the added value of nanomaterials in solar cells, a brief comeback should be presented to understand the work

Documents