Fuel 90 (2011) 3336–3342

Contents lists available at ScienceDirect

Fuel

journal homepage: www.elsevier .com/locate / fuel

Brilliant Cresyl Blue – Fructose for enhancement of solar energy conversionand storage capacity of photogalvanic solar cells

Urvashi Sharma a, Pooran Koli a,⇑, K.M. Gangotri a

a Department of Chemistry, JNV University, Jodhpur 342 033, Rajasthan, India

a r t i c l e i n f o

Article history:Received 6 January 2011Received in revised form 26 April 2011Accepted 23 June 2011Available online 13 July 2011

Keywords:Brilliant Cresyl Blue – Fructose systemCurrent–voltage characteristicsFill factorPowerH-cell

0016-2361/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.fuel.2011.06.036

⇑ Corresponding author. Tel./fax: +91 291 2614162E-mail address: poorankoli@yahoo.com (P. Koli).

a b s t r a c t

The Brilliant Cresyl Blue dye as photosensitizer, Fructose as reductant and NaOH as alkaline medium havebeen studied for enhancing the solar energy conversion and storage capacity of the photogalvanic solarcells. In this study, the observed values of electrical parameters like maximum potential, maximum pho-tocurrent, short-circuit current, power at power point, and conversion efficiency are 1115 mV, 785 lA,590 lA, 183.3 lW, and 1.9586%, respectively. In dark, the cell performance in terms of storage capacity(as half change time) was 228 min. The obtained results are highly encouraging as they are radicallyhigher than results reported so far in the field of photogalvanics. We conclude that Brilliant Cresyl Blue– Fructose system significantly enhances the performance of the photogalvanic solar cells and this systemmay be the basis for further advancement of this technology.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

The solar energy is a cheap, clean, abundant and freely availablerenewable non-conventional source for power generation. Likedye-sensitized solar cells based on ordered titanate nanotube films[1] and anatase TiO2 nanosheets [2], the photogalvanic solar celltechnique provides a promising and unexplored method for solarpower generation and storage. The photogalvanic solar cells arephotoelectrochemical cells rechargeable with light. These cells in-volve ions as mobile charges moving in solution through diffusionprocess. The solution is the absorber phase contacted by two elec-trodes with different selectivity to the redox reaction. A dye insolution is photoexcited (energy rich product), which in turn canlose energy electrochemically to generate electricity. The currentor voltage changes results from photochemically generatedchanges in solution phase redox couple. Photogalvanic cell alsohas inherent storage capacity, which makes it superior to photo-voltaic cell. There is no consumption of chemicals during chargingand de-charging of photogalvanic solar cell.

The photogalvanic effect was observed during the action of lighton the ferrous iodine- iodide equilibrium. Later on, Rabinowitch [3]suggested that it might be used to convert sunlight into electricity.To explore this idea, some photogalvanic solar cells using the Fe(II)-Thionine system as the photosensitive fluid were tested. Theobserved maximum power conversion efficiency was 3 � 10�4 per

ll rights reserved.

.

cent. The principal reason for the low efficiency was shown to bepolarization of the polished platinum electrodes and rapid loss ofthe photochemical activity of the dye. Coating the electrodes withplatinum black reduced polarization sufficiently. In principle, it ap-peared possible to make further increases in efficiency by increas-ing electrode area and decreasing the electrolyte resistance [4]. Themaximum power conversion efficiency realizable from a photogal-vanic solar cell is 5% to 9% [5].

The photogalvanic solar cells based on chlorophyll-a (Chl-a)plated Pt electrode and Chl-a free Pt electrode separated by a saltbridge-LiClO4 or KCl [6], aqueous ferric bromide [7], methyleneblue with various reducing agents [8], RuðbipyÞ2þ3 complex withferric ion [9], and microemulsions with micellar solution [10] havebeen studied.

The study of photogalvanics of toluidine blue dye with reducingagents, Fe2+, EDTA, Triethanolamine and Triethylamine have re-ported that the photo-outputs with EDTA or amines as reducingagents are higher than that for Fe2+ [11].

In the beginning, the researcher emphasized on coated Pt elec-trode with Fe2+ as reducing agent. Later on, the researcher startedusing non-coated Pt electrode with saturated calomel electrode;dye photosensitizers like Azure-A [12], Azure-C [12], Azure-B[12], Methyl Orange, Congo Red, Malachite Green, Brij-35,Safranine-O, Methylene Blue, Toluidine Blue, etc.; mixed Dyes(Methylene Blue + Azur-B) [13]; reductants like Ethylenediamine-tetraacetate (EDTA), Glucose, Diethylenetriamine Pentaacetic Acid,etc.; and surfactants like Sodiumlauryl sulfate(NaLS), Tween-80,etc.

U. Sharma et al. / Fuel 90 (2011) 3336–3342 3337

The simulation of photogalvanic solar cells consisting of Tris-(bipyrdine) Ruthenium (II) and Prussian blue was reported, andcorresponding actual device was also fabricated [14].

The principles has been presented in photogalvanic solar cells inwhich compounds are broken up by sunlight into electrochemi-cally charged fragments which usually recombine instantaneouslyif relieved of their electrical charges [15].

The photogalvanic behavior in [Cr2O2S2 (1-Pipdtc)2(H2O)2] in aHonda Cell using DMF [16], and Toluidine Blue–Arabinose andMalachite Green–Arabinose systems in presence of anionic surfac-tant NaLS [17] has been shown. The micellar effect of Tween-80 onEDTA-Safranine-O photogalvanics [18], and recently the use ofmixture of two reductants (Dextrose, EDTA) with Azur A [19] havealso been reported.

It has been seen that electrical parameters of photogalvanic so-lar cells are low, although they have shown much improvementover coated Pt electrode containing photogalvanic cells. For furtherimprovement in electrical output, the study of photogalvanic effectof Brilliant Cresyl Blue with D (-) Fructose was planned on our owninitiative. The variation of dye, reductant and NaOH have beenstudied for finding suitable composition of mixture dye, reductantand NaOH for optimum performance of the cell. The Fructose waschosen as reducing agent due to its widely known good reducingproperty in rapid Furfural test.

2. Materials and method

2.1. Materials used

Brilliant Cresyl Blue as photosensitizer, Fructose as reductantand NaOH as alkaline medium has been used. Characteristics ofBrilliant Cresyl Blue (a basic dye) are class oxazine, Molecular For-mula (M.F.) C17H20ClN3O. 0.5 ZnCl2, Molecular Weight (M.W.)385.96 and kmax 622 nm. The solutions of Brilliant Cresyl Blue,Fructose and NaOH have been prepared in doubly distilled water.

2.2. Experimental and calculation method

The experimental set up consists of a H-cell (photogalvaniccell), light source, digital pH meter-Systronics Model: 335 (formeasuring potential in millivolt-mV), microammeter-OSAW (for

Fig. 1. Photogalvanic cell set–up. A, Micro-ammeter; K, Key; R

measuring current in microampere-lA), a carbon pot log 470 K de-vice (for changing the resistance of circuit), water filter (for filter-ing infrared radiations) and a circuit key connected together asshown in photogalvanic cell set-up (Fig. 1).

The photogalvanic cell is made of glass tube of H-shape whosewall is externally blackened, but a window (1 � 1 cm2) is left inone arm. The arm with window acts as illuminated chamber andother arm without window acts as dark chamber [19]. This tubeis filled with known amount of the solutions of photosensitizer,reductant and sodium hydroxide. The total volume of the solutionis always kept 25.0 mL. A platinum electrode (as negative terminal)is dipped in illuminated chamber against window and a saturatedcalomel electrode-SCE (as positive terminal) is immersed in darkchamber. The terminals of the electrodes are connected to a digitalpH meter.

Initially, the circuit is kept open and cell is placed in dark till itattains a stable potential (dark potential – Vdark). Then, the Pt elec-trode is exposed to light radiations emitted from tungsten bulb. Awater filter is put between cell and lamp to cut off infra-red radi-ation with the aim of curbing heating effect of the cell, whichotherwise may adversely affect cell performance. On illumination,the photopotential (V) and photocurrent (i) are generated by thesystem.

After charging the cell, the cell parameters like maximum po-tential (Vmax), open-circuit potential (Voc), maximum current (imax)and equilibrium current (ieq) or short-circuit current (isc) are mea-sured. The i–V characteristics (which is studied by observingpotentials at different direct currents by varying resistance-calcu-lated by Ohm law – of the circuit) shows the highest power atwhich cell can be used.

The cell is operated at highest power (i.e., power at powerpoint-ppp) at corresponding external load, current (i.e., current atpower point-ipp) and potential (i.e., potential at power point-Vpp)for study of its performance by observing change in current andpotential with time. The error in observed values of current andpotential is +10 lA and +5 mV, respectively.

The cell performance is studied in terms of half change time(t0.5), conversion efficiency (CE) and fill factor (FF) in dark. The timetaken for fall in the power of the cell to its half value of power atpower point is called t0.5 (which is measure of storage capacity ofthe cell). The average rate of change of current over t0.5 period

, Resistance; S, Light source; V, Digital pH meter; F, Filter.

Fig. 3. Variation of potential with time (Vmax maximum potential, Voc open-circuitpotential).

3338 U. Sharma et al. / Fuel 90 (2011) 3336–3342

(Di/Dt) is calculated from (ipp � it0.5)/t0.5, where it0.5 is current att0.5. The potential corresponding to it0.5 is Vt0.5. The charging time(t) is calculated as, charging time = (time at which Vmax is obtained)– (time at which illumination is started). Photopotential (DV) isequal to Vmax � Vdark.

The CE and FF of the cell are calculated from Eqs. (1) and (2),respectively.

CE ¼ Vpp � ipp

10:4 mW cm�2 � Electrode area ðcm2Þ � 100% ð1Þ

FF ¼ Vpp � ipp

Voc � iscð2Þ

The pH of the reaction mixture is measured by a digital pH meterthrough combination electrode whose SCE part is already in useas reference electrode. Lamps of different wattage have been usedto vary the light intensity (mW cm�2) which has been measuredby Solarimeter Model–501 Cell.

3. Results and discussion

3.1. Mechanism of photocurrent generation and storage capacity

On illumination, the dye molecule gets excited. The excited dyemolecule accepts an electron from reductant and gets convertedinto semi or leuco form of dye. At platinum electrode (IlluminatedChamber-anode), the semi or leuco form of dye molecules lose anelectron and gets converted into original dye molecule. At SCE(Dark Chamber-cathode), the dye molecule accepts an electronfrom electrode and gets converted into semi or leuco form. Finally,leuco/semi form of dye and oxidized form of reductant combine togive original dye and reductant molecules [19]. This cycle goes onin cell (Fig. 2).

Both singlet and triplet excited states of dye are involved here,but triplet state being relatively more stable than singlet state hasrole in storage capacity. Thus, the photogalvanic cell can be usedfor solar energy conversion into solar power (d.c. current) and stor-age of generated solar power.

3.2. Variation of the photopotential, current and power

The photogalvanic cell consisting of 2.6 mL of M/1000 BrilliantCresyl Blue dye, 1.5 mL of M/100 Fructose, 2.2 mL of 1 M NaOHand 18.7 mL of doubly distilled water(to make total volume ofsolution 25 mL) has been studied. The specifications for this cell

Fig. 2. Mechanism of photogeneration of current in photogalvanic cell. SCE,saturated calomel electrode; D, Dye (Photosensitizer); D+, Oxidized form of Dye;R+, Oxidized form of reductant; e�, Electron.

are [Brilliant Cresyl Blue] = 1.04 � 10�4 M, [Fructose] = 6.00 �10�4 M, pH = 12.94, light intensity = 10.4 mW cm�2, tempera-ture = 310 K, diffusion Length(DL) = 45 mm, and Pt electrodearea = 1.0 � 1.0 cm2.

With time, the regular rise in photopotential has been observedas a result of increase in number of excited and electron donatingdye molecules during charging of the cell by illumination (Fig. 3).At Vmax, the number of excited and electron donating dye mole-cules is highest.

The I–V characteristics shows inversely proportional relationbetween current and potential, and 177.77 lW is the maximumpower extractible from cell at 290.0 lA, 613.0 V, and 2113.79 X(Fig. 4). The power of the cell is taken as a product of currentand corresponding potential. When potential is highest (open-cir-cuit condition), the power is zero due to zero current in the circuit.Similarly, when current is highest (closed-circuit condition), thepower is nearly zero due to nearly zero potential. Therefore, thereis maximum power of the cell [a peak in curve (b) of Fig. 4] corre-sponding to nearly middle value of short-circuits current. Further,the performance of the cell is highest at a certain resistance(2113.79 X) at which current is nearly half of short-circuit current.

During study of cell performance in absence of illumination, thepower, current and potential decreases with time (Fig. 5) as a resultof deactivation of dye molecules. The power at power point re-duces to half value in t0.5. Even after the t0.5, the cell continuouslysupply power till its complete discharge. The cell does not have

Fig. 4. Variation of potential, power and resistance with current. (a) I–V charac-teristic of the cell, (b) power vs current.

Fig. 5. Study of cell performance. (a) Power vs Time, (b) current vs time, (c)potential vs time.

U. Sharma et al. / Fuel 90 (2011) 3336–3342 3339

unlimited life as life of excited molecules is not unlimited. The cellparameters are summarized as Vdark 622.0 mV; Vmax 1037.0 mV;Voc 1034.0 mV; DV 415.0 mV; t 30.0 min; imax 759.0 lA; ieq or isc

590.0 lA; i 590.0 lA; ppp 177.77 lW; Vpp 613.0 mV; ipp 290.0 lA;t0.5 60.0 min; Vt0.5 370.0 mV; it0.5 240.0 lA; CE 1.7093%; FF0.2913; and Di/Dt 0.8333 lA min�1 .

During charging and discharging of the cell, the observed poten-tial is negative as dye donates electrons to Pt electrode. It means,the redox potential of dyes is negative.

3.3. Effect of variation of dye photosensitizer (Brilliant Cresyl Blue)concentration

The effect of variation of dye photosensitizer on cell has beenstudied by constructing seven photogalvanic cells having all factorscommon except dye concentration. Each cell has total 25 mL solu-tion including dye, Fructose, NaOH and double distilled water. Eachcell has 1.5 mL of M/100 Fructose, and 2.2 mL of 1 M NaOH. Thevolume of M/1000 dye for seven cells is 2.0 mL, 2.2 mL, 2.4 mL,2.6 mL, 2.8 mL, 3.0 mL, and 3.2 mL, respectively. In each cell, thevolume of double distilled water is taken as much as to make totalvolume of solution equal to 25 mL.

The increase in cell parameters like isc, ipp, Ppp and CE was ob-served with increase in concentration of the dye up to1.04 �10�4 M, and beyond this concentration, the decrease in theseparameters was found (Table 1). The reason for this observationmay be that on the lower side of concentration range of dye, therewill be limited number of dye molecules to absorb light in path and

Table 1Effect of variation of dye photosensitizer (Brilliant Cresyl Blue) concentrationa.

Cell parameters [Brilliant Cresyl Blue dye concentration] � 10�4 M

0.80 0.88 0.96

Vdark (mV) �638.0 �668.0 �722.0Vmax (mV) �969.0 �959.0 �1020.0Voc (mV) �966.0 �958.0 �1018.0DV (mV) 331.0 291.0 298.0t (min) 45.0 08.0 22.0imax (lA) 450.0 426.0 584.0ieq or isc (lA) 210.0 170.0 241.0i (lA) 210.0 170.0 241.0Ppp (lW) 52.39 45.00 61.49Vpp (mV) �403.0 �375.0 �473.0ipp (lA) 130.0 120.0 130.0t0.5 (min) 105.0 225.0 42.0Vt0.5(mV) �234 �212 �293it0.5 (lA) 112.0 106.0 105.0CE (%) 0.5037 0.4326 0.5912FF 0.2582 0.2763 0.2506Di/Dt (lA min�1) 0.1714 0.0622 0.5952

a At light intensity 10.4 mW cm�2, Diffusion length 45 mm, Temp. 310 K, Pt electrode

to donate electrons to Pt electrode, therefore, there is low electricaloutput at lower concentrations whereas higher concentration ofdye will not permit the desired light intensity to reach the mole-cules near the electrodes and hence, there will be correspondingfall in the power of the cell.

3.4. Effect of variation of reductant (Fructose) concentration

The effect of variation of Fructose on cell has been studied byconstructing seven photogalvanic cells having all factors commonexcept Fructose concentration. Each cell has total 25 mL solutionincluding dye, Fructose, NaOH and double distilled water. Each cellhas 2.6 mL of M/1000 dye, and 2.2 mL of 1 M NaOH. The volume ofM/100 reductant for seven cells is 0.9 mL, 1.1 mL, 1.3 mL, 1.5 mL,1.7 mL, 1.9 mL, and 2.1 mL, respectively. In each cell, the volumeof double distilled water is taken as much as to make total volumeof solution equal to 25 mL.

A general increase in cell parameters like isc, ipp, Ppp and CE wasobserved with increase in concentration of the Fructose up to6.0 � 10�4 M, and beyond this concentration, the decrease in theseparameters was found (Table 2). The reason for this observationmay be that on the lower side of concentration range of Fructose,there will be limited number of Fructose molecules to donate elec-trons to dye, therefore, there is low electrical output at lower con-centrations of Fructose whereas higher concentration of Fructosewill not permit (i) the desired light intensity to reach the dye mol-ecules, and (ii) will also hinder the motion of dye molecules to-wards the electrodes and hence, there will be corresponding fallin the power of the cell.

3.5. Effect of variation of pH

The effect of variation of pH on cell has been studied by con-structing seven photogalvanic cells having all factors common ex-cept NaOH concentration i.e. pH. Each cell has total 25 mL solutionincluding dye, Fructose and double distilled water. Each cell has2.6 mL of M/1000 dye, and 1.5 mL of M/100 Fructose. The volumeof 1 M NaOH for seven cells is 1.6 mL, 1.8 mL, 2.0 mL, 2.2 mL,2.4 mL, 2.6 mL and 2.8 mL, respectively. In each cell, the volumeof double distilled water is taken as much as to make total volumeof solution equal to 25 mL.

A general increase in cell parameters like isc, ipp, Ppp and CE wasobserved with increase in pH up to 12.94, and beyond this pH, thedecrease in these parameters was found (Table 3). The perfor-mance of the cell is estimated to be poor in relatively acidic

1.04 1.12 1.20 1.28

� 622.0 �685.0 �670.0 � 706.0�1037.0 �1115.0 �1000.0 �1002.0�1034.0 �1107.0 �998.0 �1000.0415.0 430.0 330.0 296.030.0 70.0 95.0 32.0759.0 480.0 587.0 532.0590.0 350.0 240.0 200.0590.0 350.0 240.0 200.0177.77 105.21 56.00 52.91�613.0 �501.0 �400.0 �407.0290.0 210.0 140.0 130.060.0 228.0 182.0 59.0�370 �319 �230 �224240.0 165.0 122.0 118.01.7093 1.0116 0.5384 0.50870.2913 0.2715 0.2338 0.26450.8333 0.1973 0.0989 0.2033

area 1 � 1 cm2, [Fructose] 6.0 � 10–4 M, pH 12.94.

Table 2Effect of variation of reductant (Fructose) concentration.

Cell parameters [Fructose concentration] � 10�4M

3.6 4.4 5.2 6.0 6.8 7.6 8.4

Vdark (mV) �523.0 �660.0 �705.0 � 622.0 �646.0 �697.0 �735.0Vmax (mV) �976.0 �978.0 �1009.0 �1037.0 �965.0 �1032.0 �1076.0Voc (mV) �974.0 �975.0 �1005.0 �1034.0 �965.0 �1030.0 �1075.0DV (mV) 453.0 318.0 304.0 415.0 319.0 335.0 341.0t (min) 56.0 57.0 27.0 30.0 24.0 23.0 26.0imax (lA) 490.0 600.0 470.0 759.0 478.0 410.0 487.0ieq or isc (lA) 140.0 210.0 180.0 590.0 200.0 180.0 200.0i (lA) 140.0 210.0 180.0 590.0 200.0 180.0 200.0Ppp (lW) 42.00 46.41 42.24 177.77 54.78 40.23 43.45Vpp (mV) �350.0 �357.0 �384.0 �613.0 �498.0 �447.0 �395.0ipp (lA) 120.0 130.0 110.0 290.0 110.0 90.0 110.0t0.5 (min) 53.0 111.0 66.0 60.0 100.0 45.0 48.0Vt0.5 (lV) �206.0 �211.0 �207.0 �370.0 �298.0 �390.0 �226.0it0.5 (lA) 102.0 110.0 102.0 240.0 92.0 65.0 96.0CE (%) 0.4038 0.4462 0.4061 1.7093 0.5267 0.3868 0.4177FF 0.3080 0.2266 0.2334 0.2913 0.2838 0.2169 0.2020Di/Dt (lA min�1) 0.3396 0.1801 0.1212 0.8333 0.1800 0.5555 0.2916

⁄At light intensity 10.4 mW cm�2, diffusion length 45 mm, Temp. 310 K, Pt electrode area 1 � 1 cm2, [dye] 1.04 � 10�4 M, pH 12.94.

Table 3Effect of variation of pH.

Cell parameters pH

12.80 12.85 12.90 12.94 12.98 13.01 13.04

Vdark (mV) �201.0 �654.0 �714.0 �622.0 �732.0 �665.0 �696.0Vmax (mV) �1006.0 �1023.0 �1034.0 �1037.0 �1018.0 �1042.0 �1056.0Voc (mV) �1002.0 �1023.0 �1030.0 �1034.0 �1012.0 �1040.0 �1055.0DV (mV) 805.0 369.0 320.0 415.0 286.0 377.0 360.0t (min) 69.0 110.0 87.0 30.0 17.0 102.0 29.0imax (lA) 170.0 260.0 380.0 759.0 671.0 380.0 270.0ieq or isc (lA) 90.0 120.0 350.0 590.0 570.0 340.0 150.0i (lA) 90.0 120.0 350.0 590.0 570.0 340.0 150.0Ppp (lW) 29.25 34.15 118.60 177.77 183.30 148.12 44.24Vpp (mV) �585.0 �683.0 �593.0 �613.0 �470.0 �644.0 �632.0ipp (lA) 50.0 50.0 200.0 290.0 390.0 230.0 70.0t0.5 (min) 44.0 39.0 74.0 60.0 94.0 96.0 33.0Vt0.5 (mV) �317.0 �407.0 �515.0 �370.0 �362.0 �380.0 �369.0it0.5 (lA) 46.0 42.0 115.0 240.0 253.0 195.0 60.0CE (%) 0.2812 0.3283 1.1403 1.7093 1.7625 1.4242 0.4253FF 0.3243 0.2781 0.3289 0.2913 0.3177 0.4188 0.2795Di/Dt (lA min�1) 0.0909 0.2051 1.1486 0.8333 1.4574 0.3645 0.3030

⁄At light intensity 10.4 mW cm�2, diffusion length 45 mm, temp. 310 K, Pt electrode area 1 � 1 cm2, [dye] 1.04 � 10�4 M, [Fructose] 6.0 � 10�4 M.

3340 U. Sharma et al. / Fuel 90 (2011) 3336–3342

medium. It may be due to proton attachment to heteroatom anddouble bonds in dye and reductant leading to poor electron donat-ing power of dye and reductant to Pt electrode. In alkaline medium,this effect is absent, and the anion formation of dye and reductantenhances electron donation power of dye and reductant. At veryhigh pH, OH- (from NaOH used in this system) may combine withcationic reductant (formed on electron donation from reductant todye) inhibiting regeneration of reductant in original form, leadingto poor performance of the cell.

3.6. Effect of variation of diffusion length

The effect of variation of diffusion length on cell has been stud-ied by constructing five photogalvanic cells having all factors com-mon except diffusion Length (DL).

It was observed that with an increase in DL (separation betweenthe centers of two arms of the H-cell), the photocurrent showed anincrease and potential showed decrease (Table 4). As DL increases,the current increases as conductivity of dye increases due to in-crease in volume of solution between electrodes. The potential de-creases with DL. The reason is that concentration gradient disturbs

the dye (double layer) layer on Pt electrode. As DL is small, concen-tration gradient factor is reduced and potential is increased.

3.7. Effect of variation of light intensity

The effect of variation of light intensity on cell has been studiedby constructing five photogalvanic cells having all factors commonexcept light intensity.

The photocurrent and photopotential showed an increasingbehavior with the increase in light intensity (Table 5). The increasein light intensity increases the number of photons per unit area(incident power) striking the dye (photosensitizer) moleculesaround the platinum electrode and, therefore, an increase in theelectrical output. At lower light intensity, the number of photonsmay be few in comparison to dye molecules leading to few num-bers of dye molecules for electron donation to Pt electrode. Asthe light intensity increases, the numbers of dye molecules forelectron donation to Pt electrode increases and hence electricalparameters also increases. At very high light intensity, the perfor-mance of cell decreases for probable reasons – (i) the dye mole-cules are limited in number, so large number of photons remainsunutilized, (ii) there is relatively less increase in power but high

Table 4Effect of variation of diffusion lengtha.

Cell parameters Diffusion length (Dl)

35.0 mm 40.0 mm 45.0 mm 50.0 mm 50.0 mm

Vdark (mV) �661.0 �634.0 �622.0 �615.0 �604.0Vmax (mV) �1067.0 �1054.0 �1037.0 �1028.0 �1002.0Voc (mV) �1065.0 �1050.0 �1034.0 �1025.0 �1000.0DV (mV) 406.0 420.0 415.0 413.0 398.0t (min) 69.0 63.0 30.0 41.0 53.0imax (lA) 430.0 650.0 759.0 762.0 763.0ieqor isc (lA) 290.0 432.0 590.0 592.0 598.0i (lA) 290.0 432.0 590.0 592.0 598.0Ppp (lW) 94.65 103.21 177.77 108.51 98.78Vpp (mV) �611.0 �543.0 �613.0 �539.0 �549.0ipp (lA) 155.0 190.0 290.0 201.0 180.0t0.5 (min) 43.0 95.0 60.0 51.0 79.0Vt0.5 (mV) �438.0 �369.0 �370.0 362.0 �366.0it0.5 (lA) 108.0 140.0 240.0 150.0 135.0CE (%) 0.9106 0.9920 1.7093 1.0417 0.9501FF 0.3066 0.2274 0.2913 0.1785 0.1652Di/Dt (lA min�1) 1.0930 0.5263 0.8333 1.0000 0.5696

a At light intensity 10.4 mW cm�2, temp.310 K, Pt electrode area 1 � 1 cm2, [Fructose] 6.00 � 10�4 M, [Dye] 1.04 � 10�4, pH 12.94.

Table 5Rffect of variation of light intensitya.

Cell parameters Light intensity (mW cm�2)

3.1 5.2 10.4 15.6 26.0

Vdark (mV) �588.0 �600.0 �622.0 �625.0 �611.0Vmax (mV) �967.0 �988.0 �1037.0 �1034.0 �1015.0Voc (mV) �964.0 �985.0 �1034.0 �1030.0 �1012.0DV (mV) 379.0 388.0 415.0 409.0 404.0t (min) 70.0 49.0 30.0 26.0 57.0imax (lA) 480.0 559.0 759.0 762.0 654.0ieqor isc (lA) 324.0 412.0 590.0 591.0 470.0i (lA) 324.0 412.0 590.0 591.0 470.0Ppp (lW) 57.45 98.54 177.77 134.90 123.08Vpp (mV) �460.0 �493.0 �613.0 �579.0 �600.0ipp (lA) 125.0 200.0 290.0 233.0 205.0t0.5 (min) 43.0 33.0 60.0 67.0 56.0Vt0.5 (mV) �237.0 �254.0 �370.0 �305.0 �324.0it0.5 (lA) 121.0 194.0 240.0 221.0 190.0CE (%) 0.5524 0.9475 1.7093 1.2971 1.1834FF 0.1839 0.2428 0.2913 0.2216 0.2587Di/Dt (lA min�1) 0.0930 0.1818 0.8333 0.1791 0.2678

a At diffusion length 45 mm, temp.310 K, Pt electrode area 1 � 1 cm2 , [Fructose] 6.00 � 10�4M, [Dye] 1.04 � 10�4, pH 12.94.

Table 6Effect of variation of electrode areaa.

Cell parameters Electrode area (cm2)

0.81 1.00 1.21 1.44

Vdark (mV) �676.0 � 622.0 �611.0 �580.0Vmax (mV) �1052.0 �1037.0 �1034.0 �1014.0Voc (mV) �1050.0 �1034.0 �1030.0 �1012.0DV (mV) 376.0 415.0 423.0 434.0t (min) 29.0 30.0 47.0 22.0imax (lA) 785.0 759.0 514.0 421.0ieqor isc (lA) 560.0 590.0 467.0 320.0i (lA) 560.0 590.0 467.0 320.0Ppp (lW) 165.00 177.77 142.08 92.62Vpp (mV) �550.0 �613.0 �592.0 �475.0ipp (lA) 300.0 290.0 240.0 195.0t0.5 (min) 85.0 60.0 33.0 17.0Vt0.5 (mV) �471.0 �370.0 �394.0 �370.0it0.5 (lA) 175.0 240.0 180.0 125.0CE (%) 1.9586 1.7093 1.1290 0.6184FF 0.2806 0.2913 0.2934 0.2860Di/Dt (lA min�1) 1.4705 0.8333 1.8181 4.1176

a At light intensity 10.4 mW cm�2, diffusion length 45 mm, temp. 310 K, [Fruc-tose] 6.00 � 10�4 M, [dye] 1.04 � 10�4, pH 12.94.

U. Sharma et al. / Fuel 90 (2011) 3336–3342 3341

increase in intensity leads to lower efficiency as intensity is indenominator of formula of conversion efficiency, and (iii) higherintensity causes higher heating effect on cell leading to relativelypoor performance of the cell. A water filter is used to cut off thethermal radiations and mitigate the heating effect.

3.8. Effect of variation of electrode area

The effect of variation of Pt electrode area on cell has been stud-ied by constructing four photogalvanic cells having all factors com-mon except Pt electrode area. For the observed effect of electrodearea, the better cell parameters were found for small electrodes(Table 6) owing to relatively less hindrance to diffusion of ions.The Photogalvanic cells are based on ion diffusion mechanism.

Thus, the value of cell parameters is found to be affected byvariables like dye concentration, reductant concentration, pH, DL,etc. The optimum performance of the cell can be obtained bycarefully selecting the values for all these variables, as pH 12.94,[dye] 1.04 � 10�4 M, [reductant] 6.00 � 10�4, DL 45.0 mm, Pt elec-trode 1 � 1 cm2 and light intensity 10.4 mW cm�2.

The observed highest values of cell parameters (for BrilliantCresyl Blue -Fructose system for photochemical conversion of solarenergy into electrical energy) like Vmax, charging time, imax, isc, Ppp,

3342 U. Sharma et al. / Fuel 90 (2011) 3336–3342

CE and t0.5 are-1115 mV, 8.0 min, 785 lA, 590.0 lA, 183.30 lW,1.9586% and 228 min, respectively.

Among the techniques (like photogalvanic cells, photovoltaiccells, dye-sensitized solar cells [20]), the photovoltaic techniqueis being used commercially world over for power generation, butwith disadvantage of high cost coupled with lack of storage capac-ity. It is this lacuna of photovoltaic cells, which photogalvanic cellspromise to remove as they are cheap and have inherent storagecapacity. The photogalvanic cells use very dilute solutions ofphotosensitizers, reductant, NaOH and surfactant (if used). Allthese chemicals are cheap.

4. Conclusion

We have shown that combination of Fructose as reductant andBrilliant Cresyl Blue as photosensitizer can be exploited for en-hanced performance of the photogalvanic solar cells. The resultsobtained in this work are very encouraging. For further improve-ment in performance of photogalvanic cells, the use of mixture ofphotosensitizers-one of them being Brilliant Cresyl Blue (havingabsorption throughout the whole electromagnetic spectrum withaim of using almost complete solar spectrum for solar power gen-eration) with micelles(to stabilize dye photosensitizer for betterresults) and Fructose as reductant is suggested.

Acknowledgment

The authors are thankful to Department of Chemistry, J.N.V.University, Jodhpur, Rajasthan (INDIA) for providing all necessarylaboratory facilities for research.

References

[1] Zhao L, Yu J, Fan J, Zhai P, Wang S. Dye-sensitized solar cells based on orderedtitanate nanotube films fabricated by electrophoretic deposition method.Electrochem Commun 2009;11:2052–5.

[2] Yu J, Fan J, Lv K. Anatase TiO2 nanosheets with exposed (0 0 1) facets: improvedphotoelectric conversion efficiency in dye-sensitized solar cells. Nanoscale2010;2:2144–9.

[3] Rabinowitch E. The photogalvanic effect I: the photochemical properties of thethionine-iron system. J. Chem. Phys. 1940;8:551–9.

[4] Potter Jr AE, Thaller LH. Efficiency of some iron–thionine photogalvanic cells.Sol Energy 1959;3:1–7.

[5] Albery WJ, Archer MD. Optimum efficiency of photogalvanic cells for solarenergy conversion. Nature 1977;270:399–402.

[6] Fong FK, Polles JS, Galloway L, Fruge DR. Far red photogalvanic splitting ofwater by chlorophyll a dihydrate. A new model of plant photosynthesis. J AmChem Soc 1977;99:5802–4.

[7] Zeichner A, Goldstein JR, Stein G. Photogalvanic effect in ferric bromidesolutions. J Phys Chem 1978;82:1687–92.

[8] Murthy ASN, Reddy KS. Photochemical energy conversion studies in systemscontaining methylene blue. Int J Energy Res 1979;3:205–10.

[9] Daul C, Haas O, Lottaz A, Zelewsky AV, Zumbrunnen HR. Transient processes inphotogalvanic cells: Part II. The RuðbipyÞ2þ3 /Fe3+ cell. J Electroanal Chem1980;112:51–61.

[10] Dixit NS, Mackay RA. Microemulsions as photogalvanic cell fluids. Thesurfactant thionine–iron (II) system. J Phys Chem 1982;86:4593–8.

[11] Murthy ASN, Reddy KS. Studies on photogalvanic effect in systems containingtoluidine blue. Sol Energy 1983;30:39–43.

[12] Genwa KR, Chouhan A. Studies of effect of heterocyclic dyes in photogalvaniccells for solar energy conversion and storage: NaLS–ascorbic acid system. JChem Sci 2004;116:339–45.

[13] Gangotri KM, Lal C. Use of mixed dyes in photogalvanic cells for solar energyconversion and storage: EDTA-methylene blue and azur-B system. EnergySources Part A 2001;23:267–73.

[14] Shiroishi H, Yuuki K, Michiko S, Takayuki H, Tomoyo N, Sumio T, et al. Virtualdevice simulator of bipolar photogalvanic. Cell J. Chem. Soft. 2002;8:47–54.

[15] Gangotri KM, Pramila S. Use of anionic micelles in photogalvanic cells for solarenergy conversion and storage NaLS-mannitol-safranine system. EnergySources Part A 2006;28:149–56.

[16] Pokhrel S, Nagaraja KS. Photogalvanic behaviour of [Cr2O2S2(1-Pipdtc)2(H2O)2]in aqueous DMF. Sol Energy Mater Sol Cells 2009;93:244–8.

[17] Genwa KR, Kumar A, Sonel A. Photogalvanic solar energy conversion: studywith photosensitizers toluidine blue and malachite green in presence of NaLS.Appl Energy 2009;86:1431–6.

[18] Gangotri P, Gangotri KM. Studies of the micellar effect on photogalvanics: solarenergy conversion and storage in EDTA�safranine O�Tween-80 system.Energy Fuels 2009;23:2767–72.

[19] Gangotri KM, Indora V. Studies in the photogalvanic effect in mixed reductantssystem for solar energy conversion and storage: dextrose andEthylenediaminetetraacetic acid–Azur A system. Sol Energy 2010;84:271–6.

[20] Yu J, Fan J, Zhao L. Dye-sensitized solar cells based on hollow anatase TiO2

spheres prepared by self-transformation method. Electrochim Acta2010;55:597–602.