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The pursuit of environmentally benign and efficient means of producing energy has motivated the researchers to work in the field of renewable energy sources [1-2]. Solar technologies pave way to reduce world’s over dependence on fossil fuels. Solar cells harness the clean and abundant energy of sun in an eco-friendly way by directly converting sunlight in to electricity. Present study is focused on dye-sensitized solar cells (DSSCs) also called Gratzel cells [3, 4].

A typical DSSC is composed of a few micrometer thick film consisting of metal oxide covered with a monolayer of dye, a redox electrolyte and a platinum metal electrode. One of the key components of DSSCs is semiconductor oxide electrode. Light absorption occurs in dye molecules adsorbed on porous semiconductor (TiO₂) layer. Dye excitation is followed by electron injection in TiO₂ and regeneration via a redox couple electrolyte. Much effort has gone into the study of different methods to synthesize semiconductor electrode film [5, 6]. Sol-gel technique may also allow more precise control of film thickness, particle size and porosity by controlling different parameters viz. concentration of sol, spin speed and annealing temperature [7-10]. We have attempted sol-gel dip coating process for the synthesis of TiO₂ films. Presented work reports the effects of variation of temperature at which sol is concentrated. Thickness of the films is varied by multiple coatings. Multiple coating methods help to have a better control over the thickness of thin film acting as photoanode in dye-sensitized solar cells that presents an efficient tool to enhance the light harvesting performance of the cell.

Review of Literature mentioned in the text along with main text.

The semiconductor electrode films were deposited by sol-gel dip coating technique with the help of Titanium iso-propoxide (TTIP) precursor and poly ethylene glycol (PEG) as thickness controller as reported in earlier studies [11]. Multiple coatings were used to obtain films of different thicknesses 1.2, 2.3, 3.5, 4.4 µm. The crystalline structure of the films was characterized by x-ray diffraction (XRD).

Ru(II) based N719 dye was adsorbed on to TiO₂ surface by immersing it into dye solution. A platinized ITO (indium tin oxide) coated glass was used as counter electrode. Inter-electrode space was filled by redox electrolyte. Current-voltage (I-V) characteristics of the cells under one sun illumination were recorded using a solar simulator.

Multiple coating technique.

Figure 1 displays XRD result for the synthesized TiO₂ film and it is very clear that films formed are in pure anatase form. Each peak in the spectrum can be indexed in terms of unique crystalline planes of anatase allotropic form of TiO₂.

Figure 1. XRD spectra of formed TiO₂ films

Figure 2 depicts the variation in absorbance of the films after dye adsorption with film thickness at 518 nm wavelength of light together with the theoretical results using Lambert-Beers law [12]. It is clear that dye absorption increases linearly with thickness but decreases slightly at higher thickness.

 

Figure 2. Variation in absorbance of TiO₂ thin films covered with dye

Figure 3 shows the change in short-circuit current (I_SC) of the cells with film thickness. I_SC first increases with the thickness of the electrode film and then gets a slight decrease in its values. Increased film thickness leads to adsorption of more number of dye molecules thereby increasing photocurrent but afterwards decrease in its values may be attributed due to increased series resistance of thicker films.

Figure 3. Change in I_SC values of the fabricated cells with film thickness

Short-circuit current (I_SC) values are found to decrease linearly with evaporation temperature at which sols have been concentrated as shown in figure 4.

Figure 4. Variation in I_SC values of the cells with change in evaporation temperature

This may be explained on the basis of increased degree of agglomeration and hence lower porosity at higher temperature owing to faster evaporation rate.

1. S. Rahman, A. Haleem, M. Siddiq, M. K. Hussain, S. Qamar, S. Hameed and M. Waris, Research on Dye-Sensitized Solar Cells: recent advancement toward the various constituents of dye sensitized solar celss for efficiency enhancement and future prospects, Royal Society of Chemistry, Research Advances, 2023, Vol. 13, pp 19508-19529.

2. David Fridley, Nine challenges of Alternative Energy, 2010.

3. B. O. Regan, M. Gratzel, Photoelectrochemical Solar cells, Nature, 1991, Vol. 353, pp 737-742.

4. Michael Grätzel, Solar Energy Conversion by Dye-Sensitized Photovoltaic Cells, Inorg. Chem. 2005, Vol. 44 (20), pp 6841–6851.

5.  N.G. Renganathan, M. Venkata Subramanian and S. Mohan, Electrodeposition route to synthesize Cigs films-an economical way to harness solar energy, International Journal of Engineering, Science and Technology, 2011, Vol. 3, No. 1, pp. 206-212.

6.  S. N. Sahu and K. K. Nanda, Nanostructure Semiconductors: Physics and Applications, PINSA, 2001, 67A(1), pp. 103-130.

7. A. Beganskiene, S. Sakirzanovas, I. Kazadojev, A. Melninkaitis, V. Sirutkaitis, A. Kareiva, Sol gel derived anti reflective coating with controlled thickness and refractive index, Materials Science-Poland, 2007, Vol. 25, No. 3, pp. 817-824.

8. S. Bandyopadhyay, G.K. Paul, S.K. Sen, Study of optical properties of some sol gel derived films of ZnO, Solar Energy Materials a Solar Cells, 2002, 71, pp. 103–113.

9. Qian Chen, Juha Larismaa, Anu Keski-honkola, Kati Vilonen, Outi Söderberg, Simo-Pekka Hannula, Effect of Synthesis Time on Morphology of Hollow Porous Silica Microspheres, MATERIALS SCIENCE, 2012, Vol. 18, No. 1, pp. 66-71.

10. Antonio Tricoli ,  Anna S. Wallerand and Marco Righettoni, Highly porous TiO₂ films for dye sensitized solar cells , J. Mater. Chem., 2012, 22, pp. 14254-14261.

11. Divya Jyoti, Devendra Mohan and Rakesh Dhar, Investigation of Transport and Optical Properties of Mesoporous Anatase and Rutile TiO₂ Films for Application in Dye-Sensitized Solar cells, Modern physics Letters B, 2012, Vol 26(19), pp. 1250123-8 pages.

12. B. Stuart, Modern Infrared Spectroscopy, Wiley, England, 1996.