Efficiency Of Dye-Sensitized Solar Cells Using Titanium Dioxide

Aim of the Study

Energy is an integral aspect of daily life, and the demand for it is expectantly high. Currently, over 75% of energy consumption is attributed to non-renewable sources such as oil, coal and natural gas (Carr, 2008). It is anticipated that the non-renewable sources won’t last for more than 200 years. In contrast to these sources of energy, renewable sources are thought to naturally replenish and do not pollute the environment (Dogan, 2016). As blood is to body power is to economy of any nation so without it economy will tremble and it will be difficult to run it. Everywhere throughout the world energy is one of the main issues what’s more, every nation is searching for energy assets as its demand is expanding pointedly. Non-sustainable power sources are either excessively costly or harming the earth and furthermore they are in the end going to end in not so distant future. That is the reason the world is moving towards sustainable power sources which are renewed in a moderately little timeframe.

Due to natural resource depletion and environmental demands, the world has moved to renewable energy sources. Solar energy has emerged as one of the preferred options in solving world energy crisis. In spite of the fact that hydroelectric is extremely modest sustainable power source, however, it isn’t accessible to all spots on the planet while on the other hand sunlight based can possibly assume control over the entire power generation. From time immemorial, solar energy has been a source of light and heat. In the present-day, solar energy is being used to produce electricity for domestic and industrial use.

Solar energy harvesting can be done using several technologies (Salim, 2014). Sunlight based cells are comprised of semiconducting materials, for example, silicon, which are doped with various impurities. This produces unequal dissemination of free electrons (n-type) on one side of intersection and abundance of openings (p-type) on opposite side of intersection. Sun based light has photons which hit the sunlight based board and energize the inexactly bound electrons which are intended to move just one way in sun based cells and along these lines electron-opening sets are made in individual intersections and power is acquired in outer circuit (O.V., 2010). As a result of the environmental demands, there has been a considerable decline in the use of silicon-based solar cells. Whatever the size is, a typical solar cell produces 0.5-0.6-volt DC under no load and open circuit condition. The current and voltage (power) ratting of a PV cell mainly depends on its efficiency, size (surface area) and is proportional to the intensity of light striking the surface of cell.

Schematic Diagram of the Dye-Sensitized Solar Cell

Dye-sensitized solar cells are among the options that have emerged to replace silicon-based solar cells for harvesting solar energy (Pan, 2008). These cells have been largely used due to their flexibility, low-cost, production ease, environmental friendliness and high efficiency in energy conversion. The efficiency of the solar cells used in a photovoltaic system, in combination with latitude and climate, determines the annual energy output of the system (Ito, 2012). Major improvements such as the introduction of dyes, electrolytes have improved the efficiency of these types of solar cells. At the current, they are the most efficient solar energy technologies available (Li, 2011).

For purposes of this research we aim at investigating the efficiency of dye sensitized solar cells using titanium dioxide film. Dye sensitized solar cells convert solar energy into electricity consisting of conductive cells with dye and electrolyte sandwiched in between. Dye is absorbed on the titanium dioxide as it absorbs sunlight. The low cost and efficiency of dye-sensitized solar cells has made these types of cells a center of attention and worldwide research.

The aim of the study was to investigate and determine the effect of influence of titanium dioxide on efficiency of dye-sensitized solar cells.

Schematic diagram of the dye-sensitized solar cell

This section explains the steps that were taken towards collection and analysis of statistical data.

Data was collected using both primary and secondary methods.

For purposes of this research, primary data was collected form results of the experiment. The data that was collected investigated the efficiency of dye sensitized solar cells.

The parameters that were measured were the short circuit current, the voltage for open circuit, the cell power input, the maximum obtained current, the maximum output and absorbance spectrum of the flower extract dye.

These parameters were used for calculating the fill factor and efficiency of the dye sensitized solar cell. The parameters were observed over 10 experimental periods.

Secondary data was collected from database sources depicting energy trends over the years. Secondary data will be accessed through the website https://yearbook.enerdata.net/.

An experiment was carried out to investigate the efficiency of dye sensitized solar cells using titanium dioxide film.

In order to assess the efficiency of dye sensitized solar cells using titanium dioxide, we conduct an experiment for making a comparison between two dye sensitized solar cells using zinc oxide and titanium dioxide.

The study used flower extracts as natural organic dye for the dye sensitized solar cell. Ethanol was used to obtain dye extracts from the flowers. Titanium dioxide was used as the photo electrode. The electrode was synthesized using techniques of solution extraction and was deposited on the FTO glass substrate forming a thin layer of titanium oxide film.

Data Collection Methods

The TiO₂ film underwent high temperature (about 460 °C) for about 40 minutes to enhance film strength and compactness. We studied the titanium dioxide infused with electrolyte, under light and in a dark room for its conductivity. The conductivity of light intensity, wave length and voltage were observed.

The experiment steps were repeated severally using using titanium dioxide films of different thicknesses.

Fill factor of the encapsulated dye sensitized solar cell and the energy conversion efficiency was calculated as i8n the below formulae;

Where FF is the Fill factor,  is the short circuit current,  is the voltage for open circuit, is the cell power input Imax is the maximum current obtained and  is the maximum power output observed.

Data was coded and analyzed using the Statistical Software for Statistics (SPSS).

Descriptive statistics analysis was carried out to provide a description of the data sets that were obtained during the study.

Absorbance of flower extract dye on titanium dioxide.

The following data were observed from the experiment.

Wavelength (nm)	Absorbance (a.u)
200	0.01
240	0.05
250	0.03
300	0.1
320	0.2
350	0.28
400	0.34
420	0.28
500	0.07
520	0.03

The variables wavelength and absorbance exhibit a positive upward association up to 400 nm. Beyond 400 nm, a negative downward association is exhibited.

The results depict that the absorption spectra of the dye extract were within the wavelength of 300 to 400 nm. The maximum absorption value was observed to be at 400 nm.

Results have shown that the dye absorbs light best at about 400 nm while the titanium dioxide film best absorbs light within the range 300 to 400 nm.

Photoelectrochemical performance of dye-sensitized solar cell rom flower extracts

The below table depicts the photo-electrochemical performance of de-sensitized solar cells (DSSCs) using flower extracts as dye sensitizer. The performance was measured by current-voltage curves under solar irradiation with halogen lamb of 75 mW/cm2.

Voltage (volts)	Current (MA)
0	15
0.05	14
0.1	11
0.15	9
0.23	7
0.28	6
0.35	5
0.42	4
0.47	2
0.5	0

The below table presents descriptive statistics for the two variables; voltage and current. The mean voltage is for the experiment was found to be 0.2550 and the mean current was found to be 7.30.

Statistics
	Voltage (volts)	Current (MA)
N	Valid	10	10
Missing	0	0
Mean	.2550	7.30
Median	.2550	6.50
Mode	.00a	0a
Std. Deviation	.17822	4.945
Minimum	.00	0
Maximum	.50	15
a. Multiple modes exist. The smallest value is shown

Photoelectrochemical performance of dye-sensitized solar cell rom flower extracts line graph

Voltage at maximum power output was found to be 15 with a corresponding open circuit voltage of 0. Short circuit current was found to be about 0.42 with corresponding maximum current obtained to be about 4.

The curve shows that voltage and current are inversely associated. There is an inverse proportionality between voltage and current.

Influence of thickness of electrode on cell efficiency

Thickness (μm)	Voc (V)	Isc (mA/cm2)	FF (%)	η(%)
6.3	0.63	3.33	0.73	2.33
5.9	0.65	3.21	0.63	2.25
5.2	0.68	2.97	0.59	2.22
4.4	0.71	2.88	0.61	1.90
4.2	0.72	2.62	0.63	1.72
3.8	0.76	2.45	0.67	1.56
2.9	0.75	2.30	0.71	1.32
1.0	0.73	1.92	0.68	1.17
0.7	0.79	1.34	0.72	0.88

The descriptive statistics for the variables in the above table are presented in the below table;

Descriptive Statistics
	N	Minimum	Maximum	Mean	Std. Deviation
Thickness (μm)	9	.7	6.3	3.822	1.9810
Voc (V)	9	.63	.79	.7133	.05220
Isc (mA/cm2)	9	1.34	3.33	2.5578	.63906
FF (%)	9	.59	.73	.6633	.05074
η(%)	9	.88	2.33	1.7056	.51566
Valid N (listwise)	9

Experimental Steps

The means for the variables were found to be 3.82, 0.71, 2.56, 0.66 and 1.71 for thickness, Voc, Isc, FF and efficiency respectively.

Correlation and regression analysis were performed to assess the association between variables of the study.

Correlation analysis refers to a statistical tool that determines association between variables involved in a study.

Results of correlation analysis performed are as shown below;

Correlations
	Thickness (μm)	Voc (V)	Isc (mA/cm2)	FF (%)	η(%)
Thickness (μm)	Pearson Correlation	1	-.852**	.976**	-.393	.973**
Sig. (2-tailed)		.004	.000	.296	.000
N	9	9	9	9	9
Voc (V)	Pearson Correlation	-.852**	1	-.894**	.264	-.917**
Sig. (2-tailed)	.004		.001	.492	.001
N	9	9	9	9	9
Isc (mA/cm2)	Pearson Correlation	.976**	-.894**	1	-.432	.977**
Sig. (2-tailed)	.000	.001		.245	.000
N	9	9	9	9	9
FF (%)	Pearson Correlation	-.393	.264	-.432	1	-.477
Sig. (2-tailed)	.296	.492	.245		.195
N	9	9	9	9	9
η(%)	Pearson Correlation	.973**	-.917**	.977**	-.477	1
Sig. (2-tailed)	.000	.001	.000	.195
N	9	9	9	9	9
**. Correlation is significant at the 0.01 level (2-tailed).

Association between fill factor and other variables

Fill factor was not found to be significantly statistically associated with other variables as the p-values exceeded 0.05 thereby we reject any test of correlation between FF and the independent variables.

Association between efficiency and other variables

Efficiency was found to be significantly statistically associated with the independent variables as the p-values were less than 0.05. Efficiency was found to be positively and strongly associated with thickness and Isc. However, there was found a negative association between Isc and cell efficiency.

Regression analysis was used to assess the impact that the independent variables had on factor fill and efficiency.

Factor fill

Model Summary
Model	R	R Square	Adjusted R Square	Std. Error of the Estimate
1	.548a	.301	-.119	.05367
a. Predictors: (Constant), Isc (mA/cm2), Voc (V), Thickness (μm)

ANOVAa
Model	Sum of Squares	df	Mean Square	F	Sig.
1	Regression	.006	3	.002	.717	.583b
Residual	.014	5	.003
Total	.021	8
a. Dependent Variable: FF (%)
b. Predictors: (Constant), Isc (mA/cm2), Voc (V), Thickness (μm)

Coefficientsa
Model	Unstandardized Coefficients	Standardized Coefficients	t	Sig.
B	Std. Error	Beta
1	(Constant)	1.463	.808		1.810	.130
Voc (V)	-.686	.830	-.705	-.826	.446
Thickness (μm)	.024	.045	.946	.534	.616
Isc (mA/cm2)	-.158	.164	-1.987	-.960	.381
a. Dependent Variable: FF (%)

All coefficients for both the ANOVA and regression models had p-values greater than 0.05 implying that it would not be statistically significant to regress Factor fill on Voc, thickness and Isc.

Efficiency

Model Summary
Model	R	R Square	Adjusted R Square	Std. Error of the Estimate
1	.996a	.992	.983	.06627
a. Predictors: (Constant), Isc (mA/cm2), FF (%), Voc (V), Thickness (μm)

R square equals 0.992 implying that the dependent variables explain about 99.2% of the dependent variable (efficiency).

The p-vale for the ANOVA model is less than 0.05 implying that it would be statistically significant to fit an ANOVA model for predicting efficiency.

ANOVAa
Model	Sum of Squares	df	Mean Square	F	Sig.
1	Regression	2.110	4	.527	120.076	.000b
Residual	.018	4	.004
Total	2.127	8
a. Dependent Variable: η(%)
b. Predictors: (Constant), Isc (mA/cm2), FF (%), Voc (V), Thickness (μm)

Coefficientsa
Model	Unstandardized Coefficients	Standardized Coefficients	t	Sig.
B	Std. Error	Beta
1	(Constant)	4.866	1.284		3.790	.019
Voc (V)	-3.724	1.093	-.377	-3.408	.027
Thickness (μm)	.177	.058	.680	3.073	.037
FF (%)	-1.506	.552	-.148	-2.727	.053
Isc (mA/cm2)	-.071	.221	-.088	-.322	.763
a. Dependent Variable: η(%)

The constant, Voc and thickness coefficients were found to be statistically significant in the regression model as their p-vales were less than 0.05. However, factor fill and Isc were not found to be statistically significant in the model as their p-values were greater than 0.05. We therefore fail to include the two variables in the regression model.

The regression model that shall be fit for this study for predicting efficiency is;

The regression model implies that Voc explains about -3.724 of efficiency. This means that an increase by 1 unit in Voc results to a corresponding decrease by 3.724 units in efficiency. 0.177 of efficiency is explained by thickness implying that an increase by 1 unit in thickness results to a 0.177 units increase in efficiency. 

Based on the obtained variable results, we found a cell performance with energy conversion efficiency of about 1.71% on average. The low efficiency level could be as a result of the solvent used during dye extraction. Previous studies have found similar results to this. (Zhou, 2015) found out that the energy conversion efficiency was around 0.88 per cent and water was utilized as the extracting solvent. Findings by (Al-Ghamdi, 2014) showed an energy conversion efficiency of 0.62 % and water was used as the extracting solvent. Taking higher safety on cell preparation and assessment of methods and experimental materials used could increase efficiency.

Descriptive Statistics Analysis

The results have also depicted that cell efficiency is affected by the factors; thickness of electrode film and the open circuit voltage.

A cell electrode sheet or film with high resistance due to small thickness off the sheet resistance depicts negative impacts on the performance of the cell. However, as resistance is decreased by increasing the electrode film thickness, there tends to be experienced increased cell efficiency (performance). This aspect off thickness is such that current flow in the electrode is lateral parallel to the surface of the layer. Light would be more absorbed on the electrode with greater thickness compared to the electrode with thinner thickness. For the case of this study, thickness of the titanium dioxide electrode explained about 0.177 of the cell performance. An increase by one unit in electrode thickness would result to a corresponding 0.177 units increase in the cell efficiency. A study conducted by (Xiao, 2015) showed that the regression coefficient of electrode thickness on cell efficiency was 0.234 implying a positive effect of electrode thickness on cell performance.

Findings of the regression analysis have shown that open circuit voltage has a negative impact on energy conversion efficiency. The higher the open circuit current, the greater the negative effect on cell efficiency and the lower the open circuit current, the lower the negative effect on cell efficiency. Similar findings were found by (Masanobu Yoshida, 2011). He argued that increasing open circuit voltage would result to decreased cell efficiency. Masanobu found out that increasing open circuit voltage b one percentage point would decrease cell conversion efficiency by about 0.3 percentage points. However, contradicting findings have been found by (S.NarayananM.A.Green, 2016). He carried out an experimentation with aluminium treatments for silicon cells. He found out that processing silicon solar cells under higher open circuit voltage resulted to increased photo generated carrier collection for medium resistivity substrates, and improved energy conversion efficiency for both high and medium resistivity.

Conclusion

Efficiency of sun powered cell is enormously influenced by the measure of sun oriented irradiance. It is a standout amongst the most powerful factors which change the sun based exhibit execution. It is measure of amount of solar radiation from the sun striking on particular surface. In the production of dye-sensitized solar cells each stage of the manufacturing process has a significant impact on final product outcome and quality. Among many reasons for such occurrence are the thickness of the electrode and screen printing method.

Dye-sensitized solar cells using titanium dioxide was successfully fabricated. An energy conversion efficiency of about 0.24% was observed for the flower extract cell. The flower dye absorbs observable light in the range of 300nm to 400nm with maximum peak absorbance at 400 nm. The tests carried out in a dark room under a lamp emitting all wavelengths in the visible spectrum were not found to provide consistent data due to substantial heating of the cell. The tests carried out in natural illumination exhibited stable voltage at much higher level.

Efficiency of the solar panel can further be enhanced by stopping cooling of the solar panel in the early and last hours of the day. Efficiency of solar panel can also be increased by increasing solar irradiation on solar panel.

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