History of both DSSC’s and photovoltaic
The effect of photovoltaic can also be generalized and defined as the process that converts the sunlight directly into electricity. It was discovered first in 1839 by a French physicist, Nobel Laureate and Becquerel when they critically observed the dependency voltage of light through the electrodes that emerged through electrolyte (Wei, 2010). The first silicon solar cell was manufactured in 1955 having an ability to convert only 6% (Gourbilleau, Ternon, Maestre, Palais and Dufour, 2009). The principle of generation of power by dye sensitized solar cell were later worked on by two Germany scientist by the name Tributsch and Gerischer during 1960’s and 1970’s (Spitler and Parkinson, 2009). The introduction of Nano porous electrodes was done in 1990’s by a Swiss scientist who was also a professor Ecole polytechnic in Switzerland, this introduction improved the efficiency of conversion of the dye sensitized solar cell to 7% (Mathew et al, 2014), this technology purely open up more extensive and detailed research.
The format of DSSC comprises of a cathode and an anode that contains a layer of oxide in between them, they are also sensitized by a dye and electrolyte layer. The anode structure is transparent to enable easier absorption of sunlight by solar cell inner parts. (Kalyanasundaram, 2010). Titanium dioxide mesh of oxide is fixed between the cathode and anode, this nanoparticles acts as a pathway used by the electrons (Green, 2004). The nanoparticles are coated with dyes that are able to convert the absorb light or photons into electricity or electrons (Su and Shen, 2012 ). The Iodide electrolyte helps in filling the space found between nanoparticles and also is helps in transferring electrons from the cathode to the molecules of the dye (Tributsch, H., 2009).
- The role of the anode is to send electrons through the connected wires from the solar cell, the electrons then loops back to the negative electrode (cathode) (Gong, Liang and Sumathy, 2012)
- The electrolyte and Titanium oxide nanoparticles help in transferring electrons in order to create electrical current (Gong, Liang and Sumathy, 2012).
- The TiO2nanoparticles acts as a conductor because they have a special ability of forming a wide connected network which helps the travelling of electrons (Gong, Liang and Sumathy, 2012).
- The dye molecules that coats TiO2nanoparticles when it is hit with light they produce electrons. The dye color is a core objectivity of determining the type of light to be absorbed which varies with their wavelength, the variety of light absorbed determines the amount of energy (Gong, Sumathy, Qiao and Zhou, 2017).
- The is different random travelling of electrons from one TiO2nanoparticles to other nanoparticles until the anode is reached (Nazeeruddin, Baranoff and Grätzel, 2011 ).
- The striking of photon on the surface of the dye molecule transfers energy to the dye molecule. The molecule then enters an exicited state to make it emit electrons, the electron will then travel to the TiO2nanoparticles until the anode is reached (Nazeeruddin, Baranoff and Grätzel, 2011).
- The immersion of dye-coated TiO2 molecules into Iodide electrolyte helps in replacing the lost electrons by the dye molecules (Taleb et al, 2016).
- The molecule of the Iodide in the electrolyte of Iodide helps in giving up electrons that are needed by the dye molecules, in this process the Iodide molecules will undergo oxidation to form new compound called triiodide that are light in weight which makes them float until it combines with the cathode ( and Mohammadi, 2013).
- The missing electron of the triiodide is recovered from the cathode that helps it undergo reduction and return it back to three Iodide molecules (Wu et al, 2008).
- The emitted electrons from the dye then flows from the anode through the connecting wire of the solar cell and then returns back through the cathode in the cell (Wu et al, 2008).
- There will be now restoration of electrons that are required by the dye molecules from the cathode and the process again starts over (Wu et al, 2008).
Figure 1: Operation of a dye sensitized solar cells.
Figure 2: DSSC corposants and reaction summary.
The DSSC photoactive material is the dye which is has the ability to produce electricity upon it being sensitized by the light.
The dye absorbs the photons of the directed light and uses its energy in excitation of electrons
The excited electrons is injected by the dye into TiO2
The Nano crystalline TiO2 conducts away the electrons
The circuit is complete by the chemical electrolyte to enable the electrons to return back into the dye
The Principle of a working Dye Sensitized Solar Cells
The energy is created by the movement of electrons; the energy can be stored either in batteries which are rechargeable or other electrical devices.
The efficiency of the dye sensitized solar cell will be governed by its compatibility and optimization of each and every components of the solar cell, particularly between dye molecules and Titanium dioxide semiconductor. The high surface area of the Titanium dioxide and its thickness of the film semiconductor helps to increase the loading of the dye and enhance the electron transportation (Han et al, 2009). The DSSC’s relative efficiency in light detection and absorption of light depend on the properties of the absorption of the dye used. The efficiency of the device is determined by the quantum yield for process of injection and this is known as Incident Photon to Electrical Conversion Efficiency (IPCE). The quantity can be measured by UV light using light monochromatic excitation in the laboratory.
The photocurrent in a closed circuit is measured through integrated sum of Incident Photon to Electrical Conversion Efficiency (IPCE) on the solar spectrum.
ISC = PCE(λ) * Isumλ)dλ
IPCE = 1240*(ISC/λ?)
Where:
Isum is the incident irradiance express as a function of wavelength
Isc is short circuit current
Φ is the radiant flux incident
The conversion efficiency of the sunlight to electrical power of a DSSC is expressed as follows:
= Pmax/Pin = (Isc*Voc*FF)/Pin
FF is the fill factor
Pin the input solar power into the solar cell
Voc is the voltage across the open circuit
References
Bakhshayesh, A.M. and Mohammadi, M.R., 2013. The improvement of electron transport rate of TiO2 dye-sensitized solar cells using mixed nanostructures with different phase compositions. Ceramics International, 39(7), pp.7343-7353.
Green, M.A., 2004. Third generation photovoltaics: advanced solar energy conversion. Physics Today, 57(12), pp.71-72.
Gong, J., Liang, J. and Sumathy, K., 2012. Review on dye-sensitized solar cells (DSSCs): fundamental concepts and novel materials. Renewable and Sustainable Energy Reviews, 16(8), pp.5848-5860.
Gong, J., Sumathy, K., Qiao, Q. and Zhou, Z., 2017. Review on dye-sensitized solar cells (DSSCs): advanced techniques and research trends. Renewable and Sustainable Energy Reviews, 68, pp.234-246.
Gourbilleau, F., Ternon, C., Maestre, D., Palais, O. and Dufour, C., 2009. Silicon-rich SiO 2/SiO 2 multilayers: A promising material for the third generation of solar cell. Journal of Applied Physics, 106(1), p.013501.
Han, L., Fukui, A., Chiba, Y., Islam, A., Komiya, R., Fuke, N., Koide, N., Yamanaka, R. and Shimizu, M., 2009. Integrated dye-sensitized solar cell module with conversion efficiency of 8.2%. Applied Physics Letters, 94(1), p.5.
Kalyanasundaram, K. ed., 2010. Dye-sensitized solar cells. EPFL press.
Mathew, S., Yella, A., Gao, P., Humphry-Baker, R., Curchod, B.F., Ashari-Astani, N., Tavernelli, I., Rothlisberger, U., Nazeeruddin, M.K. and Grätzel, M., 2014. Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers. Nature chemistry, 6(3), p.242.
Nazeeruddin, M.K., Baranoff, E. and Grätzel, M., 2011. Dye-sensitized solar cells: a brief overview. Solar energy, 85(6), pp.1172-1178.
Spitler, M.T. and Parkinson, B.A., 2009. Dye sensitization of single crystal semiconductor electrodes. Accounts of chemical research, 42(12), pp.2017-2029.
Su, W.A. and Shen, W.Z., 2012. A statistical exploration of multiple exciton generation in silicon quantum dots and optoelectronic application. Applied Physics Letters, 100(7), p.071111.
Taleb, A., Mesguich, F., Hérissan, A., Colbeau-Justin, C., Yanpeng, X. and Dubot, P., 2016. Optimized TiO2 nanoparticle packing for DSSC photovoltaic applications. Solar Energy Materials and Solar Cells, 148, pp.52-59.
Tributsch, H., 2009. Nanocomposite solar cells: the requirement and challenge of kinetic charge separation. Journal of Solid State Electrochemistry, 13(7), pp.1127-1140.
Wei, F., 2010. Aluminum Doped Zinc Oxide Thin Film for Organic Photovoltaics (Doctoral dissertation).
Wu, J., Lan, Z., Hao, S., Li, P., Lin, J., Huang, M., Fang, L. and Huang, Y., 2008. Progress on the electrolytes for dye-sensitized solar cells. Pure and Applied Chemistry, 80(11), pp.2241-2258.
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