INTRODUCTION:

There has been a significant increase in the use of fossil fuels as energy sources all over the world. But the problems faced are low availability of fossil fuels and the pollution caused by them to the environment. So, there is a need for renewable and sustainable energy sources such as solar energy, wind energy, hydrothermal energy, etc. Solar energy is the best form of renewable energy resource due to its abundance in nature. Converting solar energy into electrical energy is the current need of the day. So, to convert this solar energy into electrical energy, photovoltaic solar cells were invented by scientists. Researchers came up with 1^stgeneration of solar cells which were the silicon based crystalline solar cells. Even though, the efficiency of these solar cells is higher than other solar cells, their fabrication cost is high which makes them non-economical and non-commercial to use. This gave an impetus to the research for the invention of2^nd generation of solar cells which was the primitive thin film solar cell. They consist of amorphous silicon and the solar materials used in these are in powder form which increases the flexibility and decreases the weight. But, in spite of these advantages, the output efficiency of these cells was considerably low due to which there was a need of further improvements. This gave rise to the invention of Third Generation Solar Cell – Dye Sensitized Solar Cell (DSSC). A dye sensitized solar cell is composed of 4 parts - photoanode, sensitizer (dye), electrolyte, and counter electrode. A classic Dye Sensitized Solar Cell is given in Figure 1. ^[10]

Figure 1 – Schematic of a Dye Sensitized Solar Cell ^[10]

Dye-sensitized solar cells separate the two functions provided by silicon in a traditional cell design. Usually, the photoelectron source as well as to provide an electric field for the separation of charges and to create a current, a semiconductor - Silicon is used. In the dye-sensitized solar cell, the bulk of the semiconductor is used solely for charge transport, the photoelectrons are provided from a separate photosensitive dye. Charge separation occurs at the surfaces between the dye, semiconductor and electrolyte. DSSCs based on both natural and synthetic dyes have been made and an intensive research is being done to continuously improve the efficiencies of these cells. In general, the efficiency of DSSCs can be improved by -

a) Improving the material of construction of photoanode and adsorption of metal oxides to increase the active surface area. ^[2]

b) By using different sensitizers with improved electron-donor pair as well as by introducing cosensitizers and coabsorbent. ^{[4, 9]}

c) Introducing high boiling point solvent redox mediator (electrolyte) with non-corrosive properties. ^[8]

d) Improved fabrication of counter electrode by catalysts comprising of metals, metal oxides, sulphides, conductive polymers.^{[13, 14]}

This review paper consists of the working of DSSCs, their different types and will also cover the ways by which the efficiencies of DSSCs can be enhanced.

Components of DSSC:

The main components of a dye sensitized solar cell are -

1) Counter electrode (CE)

2) Photo electrode (photo-anode)

3) Photo sensitizer

4) Electrolyte with redox mediator

Following is the detailed description of each component

1) Counter electrodes (CE):

Counter electrodes generally made up of platinum or carbon filled conductive glass. Conductive glass can increase the charge transfer between CE and electrolyte interface. Platinum filled CEs have better performance because of having high conductivity and high catalytic activity. Platinum is noble metal which is very high cost and method used for preparing platinum CEs, electro -chemical deposition and sputtering consume high energy. So, carbon filled counter electrodes are preferred more to fabricate DSSCs due to their low cost and good conductivity. Role and composition of counter electrode is given in Figure 2. [16]

Figure 2 - Role and composition of Counter electrode ^[16]

Synthesis of Carbon filled counter electrodes:

Carbon material for fabrication of counter electrodes for dye sensitized solar cells is produced from carbonization of sugar free at 1400 degree celsius in the flowing argon. The produced carbon flakes are crushed in mortar pestle to convert into finer particles. Polyvinyl pyrrolidone (PVP) is used as surfactant in carbon slurry which is made up in ethanol. PVP + ethanol solution is stirred about one hour to make homogeneous solution. Then carbon is added in this solution. After this PVP + ethanol + carbon solution is kept on pot mill for 48 hours to make it homogeneous slurry. The carbon to PVP weight ratio is kept 8:1. This homogeneous slurry is coated with FTO glass substrate by doctor blade technique to make CEs. Counter electrodes is heated in the furnace up to 450 degree celsius for one hour in flowing argon. ^[16]

2) Photo electrode:

Earlier solar cells were made from semiconductors such as Si, Ga, As, Cd but when these photo-anodes were exposed to light, photo-corrosion occurred due to poor stability of photo-chemical cells. So TiO2 or ZnO semiconductor having wide bandgap and high chemical stability is used. So, photo-corrosion does not occur due to their high chemical stability. Generally, TiO₂ is used in DSSC as photo anode. ^[32]

Preparation of TiO₂ photo-anode:

Firstly TiO₂ nano-crystals are prepared using glucose and Ti(SO₄)_{2 .} 3.0 gram Ti(SO₂)₂ and 0.1 gram glucose are dissolved in 60 mL distilled water. The mixture stirred continuously for 4 hours and produced mixture is transferred in an autoclave at temperature 180°C. As made samples are rinsed with deionised water and centrifuged. Drying treatment of samples takes place at 70°C for 30 minutes. After that conductive FTO (Fluorine doped tin oxide) glass is cleaned neutral cleaner. Cleaned FTO glass is submerged in TiCl₄ solution for 30 minutes. At 70°C, FTO glasses are cleaned continuously in the solution of TICl₄. Four types of TiO₂ paste (blank, C-TiO₂-12hr, C-TiO₂-24hr, C-TiO₂-48hr) produced by TiO₂ + Ti(SO₄)₂ + H₂O are applied to prepare the different screen printing pastes. C-TiO₂-12hr means TiO₂ + Ti(SO4)₂+ H₂O mixture is heated in autoclave for 12 hr, Similarly for C-TiO₂-24hr , C-TiO₂-48hr . Pastes are coated by screen printing on TiO2 blocked FTO. After this FTO glass are kept at room temp about 5 minutes then dried treatment takes place at 125°C. This procedure is repeated many times until thickness of 13-19µm is obtained. Electrodes are submerged again in TiCl4 solution for 30 min and temperature of solution is maintained upto 70℃ after temp is increased upto 500℃ and maintained up to 30 minutes then cool down to 80℃. The electrodes were quickly moved to N719 dye solution. Acetonitrile and tetra butyl alcohol are used as solvents in the dye solution.N719 dye solution is maintained at 25℃ in the dark for 24 hr. Hence the electrodes are finally prepared. [13]

Preparation of Fe₃O₄-TiO₂ Composite photo electrode:

This type of photo electrode is fabricatedby Fe₃O₄-TiO₂ paste. This composite paste consists of 3g TiO₂ powder, 6 ml D.I. water, 0.15 ml Triton X-100, 0.05 ml Ac and 5mg Fe3O₄ powder. This paste is stirred at room temperature for room temperature for 12 hours. ^[19]

3) Photo sensitizer:

In DSSCs dyes work as photo sensitizer. As absorption of photon takes place, a dye molecule absorbed on the surface of TiO₂ gets oxidized and the excited electron is injected into nano-particles of TiO₂. Promising photo -sensitizers are polypyridyl compounds of Ru (II), for example - Ru(dcb)(bpy)_2,Ru(dcbH₂)(bpy)(PF₆)₂ and Os(dcbH₂)(bpy)₂(PF₆)₂. Natural dyes areshiso leaf pigments, Black rice, natural anthocyanins. A classic structure of photosensitizer is given in Figure 3.^[32]

Figure 3 - Structure of Photosensitizer ^[32]

(a) Ruthenium based red or N3 dye absorbed on TiO₂ surface.

(b) Cyanine dye absorbed on TiO₂ surface.

4) Electrolyte with redox mediator:

Electrolyte use in DSSC contains I^-/I^3- ion to regenerate the oxidized dye molecules. Hence electric circuit between CEs and nano -structured electrode iscompleted by mediator electrons. Examples of redox mediator are NaI, LiI and R₄NI (tetra alkyl ammonium iodide). They are dissolved in an aprotic solvent such as acetonitrile, propionitrile.^[32]

Working of DSSC:

DSSCs imitate the way in which plants harness solar energy. In a DSSC, electrons originate from a dye on absorption of light. The dye contains a conjugated system(alternating single and double bonds) that is responsible for absorption of light in the visible spectrum. Light passes through the transparent anode and cause excitation of the dye molecules. The dye molecules which are excited now inject electrons into the TiO₂ layer which acts as a semiconductor. The electrons flow through the external circuit to the Pt cathode and then flow into the iodide electrolyte. The electrolyte then transfers electrons back to the dye molecules. In the DSSC, the dye undergoes oxidation (loses an electron).The oxidized dye receives an electron from an iodide ion, which causes reduction of the dye back to its original form. The electron that returns to the DSSC from the external circuit causes reduction of the I₃^- ion back to iodide ions.

Important parameters:

A DSSC behaves like a diode in absence of light. When light is focused on a DSSC, the IV curves are further shifted down. Now current is generated in the solar cell which is directly proportional to light intensities. Current flux is observed to be constant at lower potentials. When the potential is zero, it reaches its maximum value. The current which is generated is inversely proportional to the potential. Its value is zero at the open circuit potential (V_OC).

Above this potential (V_OC), an external bias voltage is needed to power the cell. The cell can get damaged at excessively high values of this voltage. Figure 4 shows a schematic overview of an I-V curve including parameters.

Figure 4 - I-V Curve

Short circuit Current:

The short circuit current I_SC is the highest current that can be drawn from a solar cell. The cell voltage is zero at this point. Hence the generated power is also zero. The short circuit current is directly proportional to light intensity.

I_SC=I_MAX=I (V=0)

Open circuit Potential:

The open circuit potential V_OC is the highest voltage of a solar cell at a given light intensity. It is also the potential where current flow through a solar cell is zero.V_OC is also directlyproportional to light intensity.

V_OC=V_MAX=V (I=0)

Power:

The generated power P of a solar cell can be calculated by the following formula :P=V*I

Fill Factor:

The Fill factor (FF) is an important parameter that specifies the overall capabilities of a cell. It is a measure of the quality and idealness of a solar cell. The Fill factor is the ratio of maximum generated power P_max to theoretical power maximum P_theo of a solar cell. The general formula for the Fill Factor is:

FF=(P_MAX/P_THEO) = (IMP*VMP)/(ISC*VOC)

E_MP and I_MP are potential and current of the I V curve where the generated power is at themaximum.

Efficiency:

Efficiency is the most fundamental parameter which is used to compare two cells. It is defined as the ratio of maximum power generated (P_max) to incident optical power.

Efficiency = (P_MAX/P_INPUT)

Fabrication of DSSC:

Ethyl cellulose and α-terpineol are mixed in 20mL ethanol solution and stirred to prepare a screen-printable paste. After this, TiO₂ nano particles, 0.25 gm mesoporous spheres are mixed in the above solution and stirred for 10 min followed by 10 min ultrasonic dispersion. Ethanol is removed by heating and TiO₂ pastes are prepared. Self-made pastes coated with FTO glass are used to prepare DSSC photoanodes. Conductive FTO glass is washed by diluted HCl, ammonia, acetone and highly pure water. Then ozone treatment of FTO glasses is done ca. 30 min. Area of TiO₂ Coatings on FTO glass are 4mmX4mm squares. To remove organic substances, heat the coatings up to 500℃ ca. 30min. After this, photo anodes is immersed in TiO₂ solution ca. 30 min and cleaned by water. Then treated samples are heated ca. 500℃ up to 30 min. And soaked in 0.3mM N719 dye solution (in which 1:1 acetonitrile and tertbutanol worked as solvent) at room temp in dark for 24 hr for dye loading. TiO₂ photo anodes are assembled and hot sealed with sputtered counter electrodes (platinum or carbon). Liquid transfer gun is used to inject electrolyte into the cells. Figure 5 gives the structure and preparation of DSSCs. ^[11]

Figure 5 - Structure and preparation of DSSC ^[11]

Earlier, a Dye sensitized solar cell which was fabricated by Gratzel used a dye solution which was based on ruthenium with photoanode made of TiO₂ nanoparticle films of 10- m thickness and porous in nature. An efficiency of 6.8 % in power conversion was achieved by them. This proved to be a motivation for scientists to carry out further research on solar cells to achieve higher power conversion efficiencies, optimal cost and better durability so as to suffice the energy needs of future generations. There are many advantages in using DSSCs, a low ratio of price to performance, economic processing cost; it works at wide angles as well as a broad range of wavelengths, mechanical robustness, light in weight, and a transparent design which is appealing aesthetically to the consumers. Many applications require the use of DSSCs and due totheir advantages. Dye sensitized solar cells are able to give a transparent effect as well show vivid colours, and their working effectiveness in broad range of wavelengths is a desirable feature for the industry.

This study also includes various modifications in DSSCs to increase the overall efficiency of the cell, thus proving to be a better alternative for the utilization of energy.

Methods of Increasing Efficiency:

1) TiO₂nanotube arrays^[2]:

Nanostructures of metal oxides have been incorporated into dyesensitized cells to increase the area of adsorption of dye molecule on to the surface (as acoadsorbate). This improved adsorption gives a higher value of photocurrent which increases the PCE. Mesoporous TiO₂ was used by researchers to produce a considerable increase in surface area. In TiO₂ nanoparticle films, Anatase form of TiO₂ structure gave a better electron transport than the Rutile structure of TiO_2. With further research, we came to know that TiO₂ nanotubes were far better in providing efficient charge transfer than TiO₂ nanoparticles due to absence of a grain boundary. The Anodization of TiO₂ nanotube arrays in essential factor. TiO2 nanotube arrays up to about 1000 m were prepared using a variety of electrolytes which were organic, such as N-methyl formamide, ethylene glycol, dimethyl sulfoxide. The main aim to increase the area of nanotube arrays is to reduce the water content.

At the electrolyte interface, the reaction is written as

H₂O → OH⁻ + H⁺ or

OH^- → O²⁻ + H⁺

The cations’ movement to the cathode is observed and following they undergo the following reaction:

2H⁺ + 2e⁻ → H2

The oxide ions, OH− or O²⁻, migrate through the oxide layer to form TiO₂ -

Ti + OH⁻ → Ti (OH) + e⁻ or

Ti + 2O²⁻ → TiO2 + 4e⁻

Titanium hydroxide is decomposed to formTiO₂ at the oxide/hydroxide interface. F⁻ from the electrolyte migrates to the anode and undergoes the reaction:

TiO₂ + 6F⁻ + 4H⁺ → [TiF6]²⁻ + 2H₂O

Overall reaction of TiO2 nanotube arrays is -

TiO₂ + H₂O + 6F⁻ → [TiF6]²⁻ + (2)O²⁻ + OH⁻ + (2)H⁺

But, this dye sensitized cell used illumination from the backside. Hence, the sunlight that was incident on the cell, had to pass a Platinum metal coated counter electrode and an electrolyte that absorbed light around 400-410 nm. To increase the energy conversion efficiency using TiO2 nanotube arrays in DSSCs, the structure should be designed with front illumination design instead of a back illuminated DSSC. Figure 6 describes a schematic of incorporation of TiO₂ nanotube arrays.

Figure 6 – TiO₂ Nanotube Arrays ^[2]

2) Inkjet printed ionic liquid electrolyte^[8]:

The successful inkjet printing of an ionic liquid electrolyte in the dye-sensitized solar cell (DSSC) as a new sequence of cell fabrication eliminated the process of drilling holes in the substrates of dye sensitized solar cells. Reduction in the overall fabrication cost due to no addition of thermo plastic sealant as well as no requirement of glass cover to seal the cells, but also to remove the extra cell sealing step which is present in the conventional cell sealing process was achieved through this newly developed technique. The dye-sensitized solar cells which were fabricated with the help of printed ionic liquid electrolyte exhibited a good 6% enhancement in overall cell conversion efficiency (PCE) as compared to the reference cells. Another significant observation was the performance of the electrolyte printed solar cells. They retained 100% of the performance, i.e. they showed the same performance even after the accelerated ageing test for 1120 hours which was at the start and was performed under an intensity of full sunlight. The results provided us a good base for the development of this process further for the production of economic, more robust, durable DSSC panels having a large area.

The overall performance of a Dye sensitized solar cell currently depends on the composition of the ionic electrolyte and its deposition in the DSSC from among all the materials associated and steps for fabrication. Electrolytes based on solvents such as Acetonitrile (CH₃CN) which are volatile in nature were used in the fabrication of high efficiency cells but there were issues with the stability and operation of the solvent in the long run. The main complication was due to the sealing step. Tackling the problem was done by the introduction of a solvent as an electrolyte which had a relatively higher boiling point than others. It showed good stability in accelerated ageing tests. A mixture of anionic liquid with sulfolane (Z988- EL) has proved to be one of the best electrolyte formulations in terms of stability, durability and performance and there have recently been reports that it maintained more than 92% and 80% of the initial cell efficiencies which were around 8.1% over a 2230 hours long light soaking test at 60 degree Celsius and a1065 hours long thermal stability test in the dark at 80 degree Celsius respectively. The are many advantages of this electrolyte due to the solvent sulfolane that has a high boiling. It exhibits excellent properties as a DSSC solvent by conducive interaction with the I^-/I^3- redox couple. It simultaneously enhances the durability; stability and overall performance of dye sensitized solar cells when it is used as an additive in ionic liquid electrolyte. Figure 7 shows the structure of Sulfolane.^[8]

Figure 7 – Sulfolane ^[8]

The successful inkjet – printing of an ionic liquid sulfolane electrolyte in the dye-sensitized solar cell as a new cell fabrication eliminated the drilling hole in the dye sensitized cell substrates. It was mainly based on a simple drop test experiment which was performed over the mesoporous layer of TiO₂ that showed a drop pattern which was highly stable in case of sulfolane based ionic liquid electrolyte. A record 13% efficiency has been achieved through this inkjet printing.

3) Incorporation of graphene sheets in photoanode of various sizes:

For enhancing the performance of DSSC, nanostructured carbon materials such as graphene were incorporated in DSSCs^[30]. Unique optical and electronic properties like high transparency, high electron mobility along with its abundance in nature as well as it being inexpensive, were the reasons for its selection as a performance enhancer in DSSC. Its incorporation resulted in improvement in light harvesting, reduced charge recombination and increased the rate of electron transfer. It was found that the short circuit current and efficiency of a DSSC were inversely proportional to the size of graphene sheets incorporated. Studies also showed that smaller graphene sheets increased the adsorption of dye molecules on the TiO₂ surface. It was reported that the DSSCs with a graphene loading of 0.83–1 wt% yielded the highest power conversion efficiency^[30]. The photovoltaic properties of standard DSSC without any graphene and the ones with different graphene sizes are summarized in table 1^[30]. It can be clearly observed from the table that graphene acts as a performance enhancer in DSSC. Smaller the size of graphene sheets, better are the photovoltaic properties. About 49% increase in efficiency was witnessed on incorporation of 184 nm graphene sheet as compared to standard DSSC without graphene. Table 1 tells the variation in efficiencies between standard DSSC and graphene sheet incorporated DSSC.

Table 1 - Graphene Modifications ^[30]

DSSC	J_sc(mA/cm²)	V_OC (V)	FF (%)	Efficiency
Standard DSSC	9.76	0.68	66	4.43
Cells with graphene(1.2 micron)	11.87	0.68	63	5.09
Cells with graphene(444nm)	12.92	0.68	66	5.31
Cells with graphene(292nm)	13.75	0.68	60	6.15
Cells with graphene(184nm)	14.66	0.68	66	6.62

Hence it can be predicted that the small size of graphene sheets enhanced dye adsorption thereby increasing the ability of light harvesting leading to higher power conversion efficiency.

4) Titania particle size evaluation^[3]:

Particle size is one of the factor by which we can increase the power efficiency of the DSSCs. As the particle size increases, the contact area between the dispersion and the conductive surface becomes insufficient due to which there is a decrease in the Coulomb force between Titania particles, which leads to the uneven film thickness when it is applied by the spin coating technique as the TiO₂ particles do not get dispersed completely. After the film is applied, it is seen that the film thickness is uneven and it has cracks and holes on the surface. This leads to low and unstable power generation. The presence of uneven film thickness, holes and cracks has made the sintering process difficult which limited the movement of electron throughout the Titania electrode. Table 2 briefs about the variation if properties of different sized particles.^[3]

Table 2 - Titania Particle Size Evaluation ^[3]

Particle Size (nm)	Uniformity of the film thickness	Surface Condition	Sinterability	Power stability
7	Acceptable	Good	Excellent	Excellent
60	Not acceptable	Not acceptable	Acceptable	Acceptable
160	Not acceptable	Not acceptable	Not acceptable	Not acceptable

The conclusion of this experimental procedure is that the best particle size for TiO2 powder is 7nm. Best sintering conditions and one of the most stable power generations besides having the uniformity of the film thickness and considerably good surface condition are achieved. The photoanode films, mesoporous in nature, which are composed of small sized TiO₂ nanocrystalline particles provide a large surface for greater dye adsorption and facilitate electrolyte diffusion within their pores.

5) Porphyrin cosensitization^[9]:

This was one of the best researches on DSSCs as it eliminated the use of ruthenium dyes and gave an excellent output efficiency of about 11.5%.

Dye-sensitized solar cells (DSSCs) are proving to be an excellent alternative to utilize solar energy. To gain a high efficiency, it is important to improve the photo-current (J_sc) and the photo-voltage (V_oc). The conjugation framework extension and co-sensitization are effective for improving the absorption and the photo-current J_sc but often photo-voltage V_oc decreases undesirably with this. Thus, an optimized porphyrin dye was developed with a targeted co-adsorption/ co-sensitization approach for systematically improving the V_oc from 645 mV to 727 mV, 746 mV, and 760 mV, with synergistic increase in photo-current J_sc from 18.83 mA cm^-2 to 20.33 mA cm⁻². In this way, the efficiency enhanced dramatically to 11.5%, which was a record for non-ruthenium based dye sensitized solar cells using the I₂/I₃⁻ as electrolyte. These results mention and throw light upon an alternative approach for developing highly efficient DSSCs with relatively high photo-voltage V_oc using conventional iodine electrolyte. Figure 8 shows the structure of porphyrin and other co-adsorbent as well as co-sensitizer.

Figure 8 - Molecular structures of the porphyrin dyes ^[9]

XW 9: Porphyrin dye.

XW 10: Porphyrin with an additional ethylene bridge to give red shifted wavelength absorption.

XW 11: Porphyrin dye with ethylene bridge as well as auxiliary benzothiadiazole group to give further red shift from 650 to 700 and 730 nm.

CDCA: Chenodeoxycholic acid : effective co-absorbent.

C1: Co-sensitizer (having broad absorption peak at 500 nm).

WS-5: Alternative Co-sensitizer to further improve wavelength of absorption, photo-voltage V_oc and photo-current J_sc and give excellent efficiency. The best result in efficiency as well as photo-current and photo-voltage was obtained by using XW11 as the porphyrin structure with WS-5 as the co-sensitizer. An efficiency of 11.5% was achieved which was a record for non-ruthenium dyes.

Important application of DSSC^[33]:

High efficiency, cost-effectiveness, and persistent power-generation in all weathers is the need of the day for the energy industry. An all-weather Dye sensitized solar cell can generate electricity in the daytime as well as in the dark by incorporating long persistence phosphors (LPPs) into the photo-anodes which are made of TiO2 and are mesoscopic (m-TiO2) in nature. When a suffered simulated sunlight (air mass 1.5, 100 mW/cm²) illumination is incident on the DSSC, the all-weather solar cell which contains fluorescent-emitting m-TiO2/LPP photoanode yields a maximal photo conversion efficiency (PCE) of 10.08%. The red and infrared lights which are not absorbed across dye-sensitized m-TiO2 layer are stored in long persistence phosphors and are further converted into a monochromatic fluorescence for persistent dye illumination in dark conditions, yielding maximized photo conversion efficiency (PCE) up to 26.69% as well as with excellent duration lasting for several hours. Figure 9 shows the schematic of an all-weather DSSC which uses LPP to increase efficiency. ^[33]

Figure 9 - All - weather Dye Sensitized Solar Cell ^[33]

CONCLUSION:

Converting renewable solar energy to electrical energy is the need of the hour. The DSSCs being cheap and eco-friendly have a great potential to replace the traditional silicon photo-voltaics. But their commercialization is a big problem on account of their relatively low efficiency and stability to outdoor conditions such as high temperature, continuous light illumination and humidity as compared to traditional firstgeneration photovoltaic cells. The maximum efficiency reported is under 12%. The use of liquid electrolyte causes leakage problems and also its high volatility is an issue to be dealt with. So as of now the DSSCs cannot compete with traditional photovoltaic cells in the market but we predict that in near future due to intensive research going on in this field, all the limitations will be overcomed and DSSCs will rule the market.

REFERENCES:

1. AriniNuran Binti Zulkifili et al., “The Basic Research on the Dye-Sensitized Solar Cells (DSSC),” Journal of Clean Energy Technologies, Vol. 3, No. 5, September (2015).

2. Won-Yeop Rho et al., “Recent Progress in Dye-Sensitized Solar Cellsfor Improving Efficiency: TiO2 Nanotube Arrays in Active Layer,” Journal of Nanomaterials, (2015).

3. Suriati Suhaimi et al., “Materials for Enhanced Dye-sensitized Solar Cell Performance: Electrochemical Application,” Int. J. Electrochem. Sci., (2015).

4. Zhaoyang Yao et al., “Donor/Acceptor Indenoperylene Dye for Highly Efficient Organic Dye-Sensitized Solar Cells,” Journal of the American Chemical Society, (2015).

5. Lakshmi Munukutla et al., “Incorporation of Dye Sensitized Solar Cell Research Results into Solar Cells and Modules Class,” American Society for Engineering Education, (2011).

6. David Riehm, “Improving Dye-Sensitized Solar Cell Efficiency by Modification of Electrode”.

7. Michael Grätzel, “Dye-sensitized solar cells,” Journal of Photochemistry and Photobiology, (2003).

8. Syed Ghufran Hashmi, “High performance dye-sensitized solar cells with inkjet printed ionic liquid electrolyte,” Elsevier, (2015).

9. Yongshu Xie et al., “Porphyrin Cosensitization for a Photovoltaic Efficiency of 11.5%: A Record for Non-Ruthenium Solar Cells Based on Iodine Electrolyte,” Journal of the American Chemical Society, (2015).

10. Vipinraj Sugathan et al., “Recent improvements in dye sensitized solar cells: A review,” Elsevier, (2015).

11. Bing Hua, et al., "Dye-sensitized solar cells fabricated by the TiO2 nanostructural materials synthesized by electrospray and hydrothermal post-treatment", Elsevier, (2015).

12. D. Sengupta et al, " Effects of doping, morphology and film-thickness of photo-anode materials for dye sensitized solar cell application", Elsevier, (2016).

13. Aini Lin et al, "Carbon-doped titanum dioxide nanocrystals for highly efficient dye-sensitized solar cells", Elsevier, (2016).

14. Simone Casaluci et al., ”Graphene-based large area dye-sensitized solar cell modules,”, Nanoscale 8 (2016), 5368-5378.

15. I.N. Obotowo et al.," Organic sensitizers for dye-sensitized solar cell (DSSC): Properties from computation, progress and future perspectives ", Elsevier, (2016).

16. Rahul Kumar et al.," Synthesis and characterization of carbon based counter electrode for dye sensitized solar cells (DSSCs) using sugar free as a carbon material", Elsevier, (2017).

17. Isabella Zama et al, " Preparation of TiO2 paste starting from organic colloidal suspension for semi-transparent DSSC photo-anode application ", Elsevier, (2017).

18. Marina Freitag et al, " Copper Phenanthroline as Fast and High Performance Redox Mediator for Dye Sensitized Solar Cells ", ACS Publications, (2016).

19. Jung-Chuan Chou et al.," An Investigation on the Photovoltaic Properties of Dye-Sensitized Solar Cells Based on Fe3O4–TiO2 Composited Photoelectrode ", IEEE Journal of Electronic Device Society, (2016).

20. Jung-Chuan Chou et al.," Photovoltaic Performance Analysis of Dye-Sensitized Solar Cell with ZnO Compact Layer and TiO2/Graphene Oxide Composite Photoanode ", IEEE Journal of Electronic Device Society, (2016).

21. Jiawei Gong et al.,” Review on dye-sensitized solar cells (DSSCs): Advanced techniques and research trends,” Renewable and Sustainable Energy Reviews, (2017).

22. M. Z. H. Khan et. al.,” Performance improvement of modified dye-sensitized solar cells,” Renewable and Sustainable Energy Reviews, Volume 71 (2017), 602-617.

23. Xiaoqiang Yu et al.,” Influence of different electron acceptors in organic sensitizers on the performance of dye-sensitized solar cells,” Dyes and Pigments, (2014).

24. Chao-Hsuan Chang et al.,” Enhancing dye-sensitized solar cell efficiency by anode surface treatments,” Thin Solid Films, (2014).

25. Bismi Basheer et al.,” An overview on the spectrum of sensitizers: The heart of Dye Sensitized Solar Cells,” Solar Energy,(2014).

26. Samaneh Mozaffari et al.,” An overview of the Challenges in the commercialization of dye sensitized solar cells,” Renewable and Sustainable Energy Reviews, (2014).

27. Maria Laura Parisi et al.,” The evolution of the dye sensitized solar cells from Grätzel prototype to up-scaled solar applications: A life cycle assessment approach,” Renewable and Sustainable Energy Reviews, (2014).

28. S. Shalini et al.,” Review on natural dye sensitized solar cells: Operation, materials and methods,” Renewable and Sustainable Energy Reviews, (2015).

29. Geetam Richhariya et al.,” Natural dyes for dye sensitized solar cell: A review,” Renewable and Sustainable Energy Reviews, (2017).

30. Soumitra Satapathi et al.,” Performance enhancement of dye-sensitized solar cells by incorporating graphene sheets of various sizes,” Applied Surface Science, (2014).

31. Sunita Sharma et al.,” Dye sensitized solar cells: From genesis to recent drifts,” Renewable and Sustainable Energy Reviews, (2017).

32. Shashank chetty, "Overview on the dye sensitized solar cells (DSSC)", Slideshare, (2013).

Received on 26.09.2018 Modified on 30.10.2018

Research J. Science and Tech. 2019; 11(1):48-58

DOI: 10.5958/2349-2988.2019.00007.X