Comparative Study of Dye-Sensitized Solar Cell Based on Carbon ...

International Journal of Engineering & Technology IJET-IJENS Vol:12 No:05

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Comparative Study of Dye-Sensitized Solar Cell Based on Carbon Black and Graphite as Cathode Materials. Anees.U.Rehman1*, Azzam.U.Asar2*, Najeeb Ullah3* , Rehan.Ullah1*, M.imarn.A2* 1

Sarhad University of Sciences and Infromation Technology,Peshawar Pakistan 2 University of engineering and technology,peshawar 3 University of Cambridge, UK

Abstract--

In this paper, the comparative studies of dye sensitized solar cells (DSSC) manufactured with different cathode materials have been investigated. It has been observed that different cathode materials have different bandgap energies and it directly affect the efficiency of DSSC. The tested materials for counter electrode are carbon black and graphite. Although both of these materials are carbon based but there is significant difference in the photoelectric conversion efficiencies of these cells. Surface morphology of thin films, absorption spectrum after adsorbing dye were investigated for both cells by scanning electron microscopy, UV-visible spectrophotometer. The results show that carbon black (4.19 %) performs more efficient than graphite (2.10%).

Index Term-- DSSC; titanium dioxide film, carbon, graphite. I. INTRODUCTION Dye sensitized solar cells (DSSC) based on nanocrystalline TiO2 have attracted much attention since their first description at the beginning of the 1990s by O’Reagan and Grätzel [1] which gave an idea about a cheap option to expensive silicon photovoltaic cells. The cells are primarily made up of a nanostructured porous film of titanium dioxide (TiO2). The configuration of DSSC is different than ordinary photovoltaic cells. The DSSC substrate is a translucent glass slide upon which a layer of transparent conducting oxide (TCO) is to form a layer of nanoporous. This coated conductive layer on glass slide is of indium tin oxide so called indium tin oxide (ITO) glass side. The ITO has thickness of about 10μm which contains Titanium dioxide particles (radius of particle about 1015nm), and a thin layer of dye was coated on TiO2 particles again. The organic dye used was a complex containing Ruthenium (Ru) ions. In this research comparison of two cells having different cathode materials was used and later on their efficiency was compared. The cathode occupied is transparent glass and TCO while the major difference in these electrodes was the carbon black and graphite. The triiodide electrolyte was shifted into the space between the two electrodes.

semiconductor oxide and implemented with TiO2 film sensitized with a ruthenium dye for visible light absorption. Between photoreceptor layer and cathode, an electrolyte layer is added to perform oxidation-reduction reaction in the cells [2] and cathode materials to assemble the electrons and catalyze the redox couple regeneration reaction. The conversion of light to electricity in a DSSC is based on the insertion of electrons from the Photo excited state of the sensitized dye into the conduction band of TiO2. The dye is restored with electrons donated from iodide in the electrolyte. By the reduction of triiodide at the cathode, the iodide is restored and this electron migration through the external load completes the circuit. In this way, the DSSC generates electric current from light without being involved in any chemical transportation.

Fig. 1. Schematic Diagram for the Operation of DSSC

The photo-electric chemical process in DSSC is expressed in Equations from 1– 6. The photoexcited electron injects into the conduction band of TiO2 in subpicosecond time scales [2–4]. The dark reaction of Equations 5 and 6 also occur during the light-to-electricity conversion, but do not play a remarkable negative effect on photovoltaic performance of DSSCs owing to their slow reaction speed compared with that of Eq. 2 [5–7]. TiO2|S + hv ~ TiO2|S* TiO2|S* ~ TiO2|S+ + e– TiO2|2S+ + 3I– ~ TiO2|2S + I3 –

Structure and Operational Principles of Dye-Sensitized Solar Cell As shown in Fig. 1, DSSC contains a substrate of Indiumdoped SnO2 conducting glass (ITO), a nanocrystalline

I3– + 2e– (Pt) ~ 3I– I3– + 2e– ~ 3I– TiO2|S+ + e– ~ TiO2|S

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II. EXPERIMENTS The experiments on the photoelectrode focus on the influence for kinds of Nanoparticles. The research experiments show results of both the DSSCs one fabricated with Carbon Black as cathode and the other with Graphite, each with an area of 0.25cm2 giving different efficacies. Under an illumination of 100mW/cm2, the Carbon black shows efficiency up to 4% and Graphite up to 2%. In this study, we have also measured the current-voltage I-V characteristics for both these cells. The thickness of TiO2 layer for each of these cells is about 10 μm. Fig 2 shows the Scanning Electron microscope (SEM) images of Carbon and Fig 2(b) for graphite. The SEM images shows the particle spacing and as cleared that carbon particles are less spaced and while graphite particles have greater space as compared to that of carbon particles.

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DSSC modules were obtained using a digital source meter. Fig. 4 shows I-V characteristic curve for Carbon and Graphite based DSSC. The results of experiments including short-circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) and photoelectric conversion efficiency (η) for DSSC modules of Carbon Black and Graphite are listed in Table 1. The DSC can be calculated by η(%) = VOCISCFF/(Pin.A)× 100, where ISC is short-circuit current, VOC is the open-circuit voltage, FF is fill factor, A is active area of photoelectrode, and Pin is incident light power. The FF value is obtained from FF = VmIm/(VOCISC) where Vm is voltage and Im is photocurrent at maximum output power point. TABLE I Results for Carbon Black and Graphite based DSSC

Jsc (mA/cm2)

Voc (mV)

FF

Carbon

1.06E-03

0.2.0

65.1

4.192

320

44.2

2.102

Graphite

(a) SEM for Carbon Black

η (%)

Cathode material

0.490

Table I shows the results of different experiments, these experimental reading and SEM images confirmed that the η increases significantly with decrease in particle spacing.

(b) SEM for Graphite Fig. 2. Scanning Electron Microscope

(SEM) Images for Different

Fig. 4. I-V Characteristic of Carbon Black and Graphite based DSSC.

Cathodes Fig. 3. Schematic description of DSSC’s layers.

Fig. 3 shows the schematic of the DSSC layers. The assembled DSSC will be measured the I-V curve using an adjustable electric resistance, an electric meter, and a 1000W/m2 metal halide lamp. The apparatus measured voltage and current in different loads by changing value of electric resistances. The measured voltage is the opencircuit voltage (Voc) and the current is short-circuit current (Isc). III. RESULT AND DISCUSSIONS The current-voltage (I-V) characteristics of the each of these

In our experiment, the carbon black cathode consists of 20nm nano spherical particles and 15nm nano particles for that of graphite electrode. Obviously, the value of spaces between the nano particles decreases from 20nm to 15nm which causes an average increase in η of 0.73%. The results show that the increased carbon black ratio in the counter electrode improves the short-circuit current and the open-circuit voltage. The reason is that the carbon black has larger area/volume ratio and better adhesion than the graphite. IV. CONCLUSIONS The photoelectric efficiencies of a Dye Sensitized Solar Cell have been studied which use Carbon and Graphite based cathodes. In this experimental study, quantitative analysis indicates that the efficiency (η) follow a linear


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increase for both the cathodes which correspond with the decrease in spaces of cathode particles. The results indicate that Carbon Black cathode is more efficient than Graphite based cathode. The manufacture of carbon counter electrode using the mixture of carbon black and graphite receives the results that higher the ratio of carbon black, better will be the photoelectric conversion efficiency. REFERENCES [1 ]

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