Introduction
Redox couple is referred to as an oxidizing or a reducing agent. Example of a redox couple is Zn2+/Zn and Cu2+/Cu. This article explores the effect of TiO2 film proprieties in transportation of [Co (bpy) 3] II/III Redox Couple. The study of TiO2 is important since its properties: size of the pore and porosity are the main determinant of mass transportation of [Co(bpy)3]II/III. In this topic, we will be able to learn on how we can improve transportation of redox couple by being certain that Nanostructure of TiO2 is controlled in dye-sensitized solar cell. At the end of the topic, you will realize efficiency of 5.5 % at 1 sun will be shown after Nanostructure is sensitized with MK-2 dye (Kim, Ko, Hyuk & Park 2011).
Mass Transportation
Rapid recombination of electrodes observed in TiO2 will result to a problem in mass transportation of TiO2 electrodes and low diffusion coefficient. In a situation where there is poor mass transport, an increased series of resistance which will result to an observation of some little movement of dye regeneration and fill factor is likely to be observed (Hong, Shores & Elliott 2010). Researchers have modified the ligands of cobalt in order to solve this problem of mass transport. Even though the problem is not well solved, researchers came up with the following process to solve the mass transport problem (Kim, Ko, Hyuk & Park 2011; Grätzel 2005).
Turning the Pore Size and Porosity of Tio2 Films
The changing of the ratio of TiO2 to ethyl cellulose from 1:0.2 to 1:0.5 will tend to improve the mass transport of redox couple. Through an experiment, the porosity after mixing TiO2 with the paste is approximated to be 0.56. In a bar graph you will realize an increase in voltage will result to an increase in porosity. A translation of this is: [Co (bpy) 3] II/III Redox couple is a great dependent of porosity. High light intensity generates CO111 due to the dye produced. Also, after the experiment, you will realize that the main reason of a problem of mass transport is low porosity. This is observed through the diminishing of linearity when plotting the graph Jsc against light intensity. This portrays a reduction of porosity (Kim, Ko, Hyuk & Park 2011; Koo, Park, Yoo, Kim & Park 2008).
The pore size also plays a great role in improving the transportation [Co (bpy) 3] II/III Redox couple. Large pore sizes are likely to allow bulky cobalt complexes as compared to small sizes.
Use of Photocurrent Generation in Investigating the Effect of Mass Transport
Generation efficiency is the ratio the number of electrons collected without a problem in mass transport to the number of electrons collected with mass problem (elections controlled without a mass problem: electrons controlled with mass problem). These electrons are related to photocurrent density. Generation efficiency can be measured from saturated photocurrent density with photocurrent density at the moment of turning on the light. You will realize cobalt redox couple will not efficiently be utilized as compared to injected electrons from the dye. In an experiment, the graph of regularity against light intensity will show that regularity generation reduces with increasing light intensity. Linearity is a significance of increasing light intensity (Kim, Ko, Hyuk & Park 2011; Wang, Nicholson, Peter, Zakeeruddin & Grätzel 2010).
In conclusion, the mass transport of [Co (bpy) 3] II/III Redox is improved by simply having control of the pore size and porosity of mesoporous TiO2 films. A good structure for the bulky cobalt oxide through experiment is approximately found to be 60% porosity and 24nm pore size.
Reference List
Grätzel, M 2005, “Solar energy conversion by dye-sensitized photovoltaic cells”, Inorganic Chemistry, vol. 44, no. 20, pp. 6841–6851.
Hong, J, Shores, M & Elliott, C 2010, “Establishment of Structure-Conductivity Relationship for Tris(2,2′-bipyridine) Ruthenium Ionic C60 Salts”, Inorganic Chemistry, vol. 49, pp. 11378-11385.
Kim, H, Ko, S, Hyuk, I & Park, N 2011, “Improvement of mass transport of the [Co(bpy)3]II/III redox couple by controlling nanostructure of TiO2 films in dye-sensitized solar cellsw”, Chemical Communications, vol. 47, pp. 12637–12639.
Koo, HJ, Park, J, Yoo, B, Kim, K & Park, NG 2008, “Size-dependent scattering efficiency in dye-sensitized solar cell”, Inorganica Chimica Acta, vol. 361, no. 3, pp. 677–683,
Wang, HX, Nicholson, PG, Peter, L, Zakeeruddin, S M & Grätzel, M 2010, “Transport and interfacial transfer of electrons in dye-sensitized solar cells utilizing a Co(dbbip)2 redox shuttle”, The Journal of Physical Chemistry C, vol. 114, pp.14300–14306.