Photo electrochemical cells are another method for generating electricity. Although they aren't cost-effective for large-scale power production, but they may be quite helpful for producing energy in applications like satellites and traffic lights in outlying places, where other options aren't viable. Therefore, solar electricity has practical but limited uses, which will undoubtedly expand as the price of photoelectrochemical cells decreases. The photogalvanic cells as described in the present research work are energy devices as they provide for a route for simultaneous solar energy conversion and its storage. The study of photogalvanics of Gentian Violet- Ascorbic acid- Ammonium lauryl sulphate has been studied in alkaline medium at low intense light with aim of searching relatively proper combination of chemicals like photosensitizer, reductant and surfactant for further enhancing the efficiency of PG cell.

How efficient is a Photogalvanic solar cell at converting the sun’s energy into electrical energy? How much power does a PG solar cell produce? The objective of this experiment is to explore PG solar cells as renewable energy sources and test their efficiency in converting solar radiation to electrical power.

An investigation on the photogalvanic effect was carried out by Rathore and Singh[23] using a Janus green B-DSS-EDTA system. As a reductant, EDTA is employed in this process, while the azo dye Janus green B is used as photo sensitizers. At its power point, the system is capable of producing power equal to 164.1 microwatts. The fill factor for the system is 0.33, while the system's conversion efficiency is 1.58%. In the dark, the cell operates for 180 minutes. The scientific society has used different photosensitizers, surfactants, reductants in PG cells for conversion of solar energy into electrical energy but no attention has been paid to the use of this system containing Gentian Violet cationic dye, Ammonium lauryl sulphate and Ascorbic acid chemicals as energy material to enhance the power output and performance of the PG cell. Therefore, the present work was undertaken to obtain better performance and commercial viability of the PG cell.

Gentian Violet, ascorbic acid, Ammonium lauryl sulphate and NaOH of Loba Chemie were used in the present work. Solutions of ascorbic acid, Gentian Violet, ALS and NaOH (1N) were prepared in double distilled water (conductivity 3.5 × 10^-5 Sm^-1) and kept in amber coloured containers to protect them from sun light. Gentian Violet dye (Scheme 1) is dark brown-purple crystal with metal luster, soluble in water and stable under normal temperature and pressure. Its molecular formula and molecular weight C₂₅N₃H₃₀Cl and 407.99 g·mol⁻¹respectively. A solution of Gentian Violet, ascorbic acid, Ammonium lauryl sulphate and NaOH was taken in an H–type glass tube which was blackened by black carbon paper to protect from sun light. A shiny Pt foil electrode (1.0 x 1.0 cm²) was immersed in one limb of the H–tube and a saturated calomel electrode (SCE) was immersed in the other limb. Pt-electrode act as a working electrode and SCE as a counter electrode. The whole system was first placed in the dark till a stable potential was attained, then the limb containing the Pt-electrode was exposed to a 200 W tungsten lamp (Philips). A water filter was used to cut off thermal radiation. A digital multimeter (HAOYUE DT830D Digital Multimeter) was used to measure the photo potential and current generated by the system respectively. The i-V characteristics were studied by applying an external load with the help of Carbon pot (log 470 K) connected in the circuit the PG cell set-up is shown in figure 5.

(a) Effect of variation of Gentian Violet, ascorbic acid and ALS concentration:

The impact of variation of Gentian Violet, ascorbic acid and ALS concentration are given in table 1. The changes in dye concentration were also studied by using solution of Gentian Violet at different concentrations. It was observed that the photopotential, photocurrent and power increased with increasing in concentration of the Gentian Violet. Maximum values of electrical output were obtained for a particular value of Gentian violet concentration (21 x 10^-6M), above which a decrease in electrical output of the PG cell was observed. Low electrical output observed at the minimum concentration range of dye due to limited number of Gentian violet molecules to absorb the major part of the light in the path, while higher concentration of Gentian violet again resulted in a decrease in electrical output because intensity of light reaching to those dye molecules which are near to the electrode decreases due to absorption of the major portion of the light by the Gentian violet molecules present in the path. Therefore corresponding fall in the electrical output. With increasing the concentration of the ascorbic acid, photopotential, current and power were found to increase till it reaches a maximum value at 12 x 10^-4 M. These values are 805.0 mV, 761.0 µA and 612.60 mW respectively. On further increase in concentration of ascorbic acid, a decrease in the electrical output of the cell was observed. The fall in power output was also resulted with decrease in concentration of ascorbic acid due to less number of molecules available for electron donation to the Gentian Violet dye. On the other hand, the movement of dye molecules hindered by the higher concentration of the ascorbic acid to reach the electrode in the desirable time limit and it will also result into a decrease in electrical output. The electrical output of the cell was increased on increasing the concentration of ALS. A maximum (805.0 mV, 761.0 µA and 612.60 mW) result was obtained at a certain value (16 x 10^-4 M) of concentration of ALS. On further increasing the surfactant concentration it react as a barrier and major portion of the surfactant photobleach the less number of dye molecules so  that a down fall in electrical output was observed.

(b) Effect of variation of pH

PG cell containing Gentian Violet – ascorbic acid –ALS system was found to be quite sensitive to pH of the solution. It was studied that there is an increase in the electrical output of the system on increases the pH. At pH 11.68 a maxima was obtained in photopotential, photocurrent and power (805.0 mV, 761.0 µA and 612.60 mW). On further pH increases, there was a decrease in electrical output. The optimum electrical output was obtained at particular pH value; it may be due to better availability of ascorbic acid in donar form at that pH value. The results showing the impact of pH are represented in the table 2.

(c) Impact of diffusion length

The impact of variation of diffusion length (it is distance between the two electrodes) on the current parameters of the cell (i_max, i_eq and initial rate of generation of photocurrent) was studied using H-shaped glass cells of different dimensions. It was observed that in the first few minutes of illuminations there is sharp increase in the photocurrent. As consequences, the maximum photocurrent (i_max) increase in diffusion length because path for photochemical reaction was increased, but this is not observed experimently whereas equilibrium photocurrent (i_eq) decreased linearly. Therefore, it may be concluded that the main electroactive species are the leuco or semi form of dye (photosensitizer) in the illuminated and dark chamber respectively. The ascorbic acid and its oxidation product act only as electron carriers in the path. The results are given in table 3.

(d) Impact of light intensity

The effect of light intensity was studied by using intensity meter (Solarimeter model-501). It was found that photocurrent showed a linear increasing behaviour with the increase in light intensity whereas photo potential increases in a logarithmic manner. The impact of change in light intensity on the photo potential and current is graphically represented in figure 1.

(e) Current-Voltage (i-V) properties of the cell

The short circuit current (i_sc) 761 µA and open circuit voltage (V_oc) 805 mV of the PG cell were measured with the help of a microammeter (keeping the circuit closed) and with a digital pH meter (keeping the circuit open), respectively. The photo current and potential values in between these two extreme values were recorded with the help of a carbon pot (log 470 K) connected in the circuit of multimeter, through which an external load was applied. The i-V properties of the PG cell containing Gentian Violet, Ascorbic acid and ALS chemicals is graphically shown in figure 2 and summarized in table 4. It was observed that i-V curve deviated from its regular rectangular shape.  A point in the i-V curve, called power at point (pp), was determined where the product of  photo current (i_pp) 370 µA and potential (v_pp) 210 mV was maximum. With the help of i-V curve, the fill-factor was reported 0.1027 by using the formula:

The performance of the PG cell was observed by applying an external load (necessary to have current at power point) after terminating the light source as soon as the potential reaches at a constant value. The performance was determined in terms of t_1/2, i.e., the time required in fall of the power output to its half at power point in dark. It was observed that the cell containing Gentian Violet- Ascorbic acid-ALS can be used in dark for two hours. With the help of photo current and potential values at power point and the incident power of radiations, the conversion efficiency of the cell was determined as 0.74 % using the formula.

The results are graphically represented in time-power curve (figure 3).

3. Mechanism

When the dye molecule is excited by the light in the presence of electron donating substance (ascorbic acid), the dye rapidly changed into colorless form. The dye now acts as a powerful reducing agent and can donate electron to other substance and reconverted to its oxidized state. On the basis of earlier studies a tentative mechanism in PG cell shown in figure 4.

Fig. 4 Scheme of mechanism

SCE = Saturated calomel electrode                  D = Dye (Photosensitizer)

R = Reductant                                                   D = Semi & Leuco form

The PG cell have inbuilt storage capacity  and stored energy can be used in absence of light whereas photovoltaic cell needs extra hardware as battery for energy storage, PG cells are favourable than photovoltaic cells because low cost materials are used in this system. The conversion efficiency, storage capacity, power at power point and fill factor are recorded as 0.74 %, 2 hours, 77.70 µW and 0.1027 respectively in Gentian Violet  - Ascorbic acid – ALS system. 

1. Hodgson P.E., The Energy Crisis, Corpus Christi College Oxford, 140, (2008)

2. Bard A. J, Memming R. and Miller B., Terminology in semiconductor electrochemistry and photoelectrochemical energy conversion,  Pure and Appl. Chem.,       63, 569 (1991)

3. Kamat P.V., Karkhanawala M.D.  and Moorthy P.N., Study of Ferrous- Thionine System Part II- Power  Output in Homogeneous & Heterogeneous Type Photogalvanic Cells, Indian J. Chem.,18A, 210 (1979)
4. Rabinowitch E., The Photogalvanic Effect I: The Photochemical Properties of the Thionine-Iron System, J. Chem. Phys., 8, 551 (1940)

5. Rabinowitch E., The Photogalvanic Effect II: The Photogalvanic Properties of Thionine-Iron System, J. Chem. Phys., 8, 560 (1940)

6. Rideal E.K.  and Williams E.G., The Action of Light on the Ferrous Iodine Iodide Equilibrium, J. Chem. Soc. Trans., 127, 258 (1925)

7. Tamilarasan R. and Natrajan P., Photogalvanic Cell: Iron (II) - Poly (N–acrylamidomethyl thionine) System, Indian J. Chem., 20A, 213 (1981)

8. Murthy A.S.N. and Reddy K.S., Studies on photogalvanic effect in system containing Toluidine blue,        Solar Energy, 30, 39 (1983)

9. Rohatgi-Mukherji K.K., Roy M. and Bhowmik B.B., Photovoltage Generation of the  Phenosafranine Dye‑EDTA Sandwich Cell, Solar Energy, 31, 417 (1983)

10. Ameta S. C., Ameta R.C., Bala M and Dubey T.D.,   Use of toluidine blue – diethylenetriamine penta      acetic acid (TB - DTPA) system in photogalvanic cell for solar energy conversion, J. Chim. Phys., 88, 191 (1991)

11. Ameta S. C. , Khamesra  S. , Chittora A. K. and Gangotri K. M., Use of sodium lauryl sulphate in a photogalvanic cell for solar energy conversion and storage: Methylene blue-EDTA system, International     journal of energy research,13, 643 (1989)

12. Gangotri K.M., Genwa K. R., Kalla P., Regar O.P., Lal C. and Meena R., Photogalvanic Cells as a Device for Solar Energy Conversion and Storage, Asian J. Chem. Reviews., 5, 69 (1994)

13. Gangotri K.M., Regar O.P., Lal C., Kalla P. and Meena R., Use of micelles in photogalvanic cell for solar energy conversion and storage: Toludine blue-glucose-Acetyl pyridinium chloride system, The                Arabian J. Sci.  Engg., 22, 115 (1997)

14. Genwa K.R.and Chouhan A., Role of heterocyclic dye (Azur A) as a photosensitizer in photogalvanic     cell for solar energy conversion and storage: ALS-ascorbic acid system, Solar Energy,80, 1213 (2006)

15. Genwa K.R. and Singh K., Development of photogalvanic cell and its application in solar energy conversion and storage Int. J. Chem., 1, 542 (2012)

16. Genwa K. R. and Singh K., Optimum efficiency of Photogalvanic cell for solar energy conversion: Lissamine green B-ascorbic acid-ALS System, Smart Grid and Renewable Energy, 4, 306 (2013)

17. Genwa K. R.  and Singh K., Use of Bromocresol green- ascorbic acid-ALS System in photogalvanic cell for solar energy conversion and storage, J. Indian Chem. Soc., 90, 813 (2013)

18. Genwa K. R. and Sagar C. P., Xylidine ponceau dye based photogalvanic cell: Energy conversion for sustainable development. Eur. Chem. Bull. 3, 76 (2014)

19. Gangotri K. M. and Mohan, “Use of Trypan blue-Arabinose System in Photogalvanic Cell for Solar Energy Conversion and Storage.” Int. J.  Eng. Sci. and Res. Tech. 3, 6, 447-454 (2014)

20. Mohan and Gangotri K. M., “The optimum conversion efficiency in nile blue arabinose system by photogalvanic cell.” Advances in Energy Research. 3, 3, 143-155 (2015).

21. Gangotri P. and Koli P., Study of the enhancement on photogalvanics: solar energy conversion and  storage in EDTA-safranine –O-ALS system. Sustainable Energy Fuels, 1, 882 (2017)

22. Koli P., Photogalvanic effect of natural photosensitizer (crude Spinach extract) in artificial light for simultaneous solar power generation and storage. Environ. Prog. Sustainable Energy, 37, 1800 (2018)

23. J. Rathore and K. Singh. “Use of Janus green B as photosensitiozer in EDTA-DSS system for photogalvanic conversion and storage of solar energy.” Vidyabharati International Interdisciplinary Research Journal (Special Issue), International Conference on Emotions and Multidisciplinary Approaches-ICEMA 2021, (2021) 546. ISSN 2319-4979.