Dye Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) was fabricated using natural dyes extracted from krokot (Portulaca Oleracea. L). The effect of dye acidity was investigated on natural pH extract, 5.00, 4.00 and 3.00 of pH. The efficiency and stability DSSCs as a function of the dye acidity was studied. The result of the UV-Vis shows that the absorption of wave-length from dye extract of krokot is located in the visible region with the absorbance peak in 410.5 nm and 664.5 nm which are the peak of chlorophyll. The efficiency of extract krokot dye sensitized solar cells was decreasing  6.88 x 10<sup>-3</sup> %  to  0.42 x 10<sup>-3</sup> % when pH of the dye was adjusted from 6.27 to 3.00. DSSCs stability was also decreased look for efficiency loss from 5.27% to 97.49% in the same conditions.

Boron-dipyrrin dyes, through rational design, yield promising new materials. With strong electron-donor functionalities and anchoring groups for attachment to nanocrystalline TiO(2), these dyes proved useful as sensitizers in dye-sensitized solar cells. Their applicability in a solid-state electrolyte regime offers additional opportunities for practical applications.

A simple and cost-effective chemical precipitation method for the synthesis of Nb 2 O 5 nanoparticles is reported. The as-synthesized powder is amorphous and after annealing at 500 C the crystalline phase is observed, which is then used for the preparation of photoelectrode material sensitized with N3 dye toward dye sensitized solar-cell application. The effect of Nb 2 O 5 layer over TiO 2 by making a bilayer structure for dye-sensitized solar-cell application is studied. The device performance is studied using the current density-voltage (J-V) curve as well as by external quantum efficiency measurement (EQE). Furthermore, the behavior of electron in the device is studied by electrochemical impedance spectroscopy (EIS) measurement. It is observed that the amount of dye loading increases with optical reflection for the bilayer structure, which leads to the improvement in J SC along with EQE. The maximum power conversion efficiency obtained for the bilayer structure is 5.26%.

In this article, photovoltaic performance of dye-sensitized solar cells (DSSCs) has been improved by integrating one-dimensional (1-D) plasmonic Ag nanowires into the mesoporous TiO 2 photoanode. We fabricate series of DSSCs by varying the concentrations of Ag nanowires ranging from 0.0 to 1.2 wt.% to evaluate the performance of DSSCs. The localized surface plasmon resonance (LSPR) of Ag nanowires is utilized to enhance light absorption of dye molecules in the mesoporous TiO 2 photoanode. We found that a 0.9 wt.% of Ag nanowires in the TiO 2 photoanode gave an optimum DSSC performance with an enhancement of short circuit current density and power conversion efficiency from 17.14 to 20.30 mA/ cm 2 , and 7.57e9.41% respectively as compared to DSSC without Ag nanowires. The enhancement in photovoltaic performance was ascribed to the improvement in light harvesting by LSPR from Ag nanowires.

Hole transporting material (HTM) is a significant component to achieve the high performance perovskite solar cells (PSCs). Over the years, inorganic, organic and hybrid (organic-inorganic) material based HTMs have been developed and investigated successfully. Today, perovskite solar cells achieved the efficiency of 22.1 % with with 2,2',7,7'-tetrakis(N,N-dip -methoxyphenyl-amine) 9,9-spirobifluorene (spiro-OMeTAD) as HTM. Nevertheless, synthesis and cost of organic HTMs is a major challenging issue and therefore alternative materials are required. From the past few years, inorganic HTMs showed large improvement in power conversion efficiency (PCE) and stability. Recently CuO x reached the PCE of 19.0% with better stability. These developments affirms that inorganic HTMs are better alternativesto the organic HTMs for next generation PSCs. In this report, we mainly focussed on the recent advances of inorganic and hybrid HTMs for PSCs and highlighted the efficiency and stability of PSCs improved by changing metal oxides as HTMs. Consequently, we expect that energy levels of these inorganic HTMs matches very well with the valence band of perovskites and improved efficiency helps in future practical deployment of low cost PSCs.

Porous hollow tin oxide (SnO 2) nanofibers and their composite with titanium dioxide (TiO 2) particles (Degussa P25) were investigated as a photoanode for dye-sensitized solar cells. Incorporation of TiO 2 particles in porous hollow SnO 2 fibers enhanced the power conversion efficiency (η) from 4.06% to 5.72% under 100-mW/cm 2 light intensity. The enhancement of efficiency was mainly attributed to increase in current density (J sc) and improvement in fill factor (FF). Increase in J sc was caused by higher dye loading as indicated by UV-Vis absorption spectra and the improvement in FF was attributed to faster charge transport time as obtained from transient analysis. The microstructure of SnO 2 fibers was studied using transmission electron microscope, scanning electron microscope, and X-ray diffraction. The electron transfer and recombination life times were studied using transient analysis, whereas interfacial charge transfer was studied using electrochemical impedance spectroscopy.

In the recent times sustainable energy forms have become more and more the focus of attentions. One of the important sources for renewable energy is solar power. Since solar energy is abundant and free to use, especially in a tropical countries solar cell are the promising source of green energy. Dye sensitised solar cells (DSSC) are considered one of the most promising photovoltaic technologies as an alternative to traditional silicon-based solar cells, for their compatibility with low-cost production methods, use of natural ingredients , their peculiar optical and the high indoor efficiency. The DSSC is a device that involves micro-porous titanium oxide (TiO2) as a semiconducting electrode, sensitised with a metallo-organic or organic dye and electrolyte solution containing a redox component. This paper presents the fabrication of DSSC using natural dyes. In this research different natural extract are employed as the dye for TiO2-based DSSC. TiO2 powder was coated on top of Indium- Doped Tin Oxide (ITO) conductive glass and calcined at different time. This work shows the relation between efficiency of DSSC with respect to calcined time and different dyes.

Abstrak Dye-sensitized solar cell (DSSC) merupakan salah satu dari sel-sel listrik fotokimia yang terdiri dari fotolektroda, pewarna, elektrolit, dan counter elektroda. Tujuan menggunakan pewarna pada DSSC guna memperluas spektrum absorpsi pada cahaya tampak karena cahaya tampak memiliki sekitar 96% energi dari cahaya matahari.Telah dilakukan fabrikasi DSSC dengan menggunakan dye ekstrak daun binahong (Bassela rubra linn) dengan variasi perendaman TiO 2 dengan teknik pelapisan Spin Coating. Variasi perendaman TiO 2 yang digunakan yaitu substrat TiO 2 yang direndam dalam dye selama 4 jam, 8 jam, 12 jam, 24 jam dan 36 jam. Berdasarkan hasil pengujian menggunakan sumber cahaya lampu halogen. diperoleh karakteristik dari DSSC tersebut adalah Voc 0,177 V, Isc 0,00038 A, P max 2,32 x 10-5 Watt, FF 5,09 x 10-5 untuk sampel ekstraksi daun binahong, Voc 0,1075 V, Isc 0,00012 A, P max 5,22 x 10-5 Watt, FF 6,23 x 10-5 untuk sampel ekstraksi euphorbia. Sedangkan untuk sampel ekstraksi daun rhoeo discolor diperoleh Voc 0,370 V, Isc 0,00035 A, P max 5,45 x 10-5 Watt, FF 0,057. Dengan teknik perendaman TiO 2 pada masing-masing dye akan menghasilkan nilai tegangan dan arus yang lebih besar dan waktu preparasi yang lebih efisien. Pada penelitian ini telah berhasil dibuat elektroda foto-anoda berbahan titanium dioksida (TiO2) ukuran nanopartikel berbentuk film tebal (thick film) yang dideposisikan diatas gelas transparan konduktif FTO (fourine doped-tin oxide) dengan metode spin coating, suatu metode percepatan larutan pada substrat yang diputar. Hasil menunjukkan bahwa pewarna alami dari ekstraksi bahan alam memiliki spektrum absorbansi kisaran 300-520 nm yang merupakan zat hijau daun (klorofil) dan konduktivitas terbesar dimiliki oleh daun binahong. Foto-anoda TiO2 kemudian diaplikasikan sebagai elektroda kerja pada DSSC dengan ekstrak daun binahong (Bassela rubra linn) sebagai sensitizer. Dari hasil pengujian menggunakan solar simulator AM 1.5G (100 mW/cm2) didapatkan bahwa volume prekursor TiO2 mempengaruhi unjuk kerja sel surya DSSC dan diperoleh overall conversion efficiency mencapai 0,01 % untuk dye daun binahong, 0,023% untuk dye bunga euphorbia dan 0,024% untuk dye rhoe discolor.

— In solar photovoltaic system, the Dye-Sensitized solar cell (DSSC) has been regarded as one promising alternative way for electrical power generation. In this work, DSSCs have been fabricated and characterized, the natural dyes extracted from Amaranthus gangeticus leaves, Basella alba fruits have been used as photo-sensitizer. The mixture of dyes extract from Syzygium cumini and Amaranthus gangeticus has also been used here. The surface morphological study of TiO2 film represents more roughness and crystallity. The nanocrystalline TiO2 film deposited on the SnO2:F (FTO) coated glass substrate has been used as the dye absorber, Carbon Counter Electrode (CCE) and KI/I2 electrolyte have also been used to fabricate the DSSC. The TiO2 photo-electrodes have been sensitized with amaranth dye in three different seasons, winter, summer and autumn. Maximum efficiency of 0.413% has been measured in autumn conditions. Then another two films have been sensitized with Basella alba and mixed dye of amaranth and Syzygium cumini in autumn conditions. The performance of DSSCs has been tested under solar simulator AM 1.5 illumination. The Basella alba and mixed dye-sensitized solar cell show the efficiency of 0.115% and 0.084% respectively in autumn seasonal conditions.

A B S T R A C T The energy demand is ever increasing on aspect of primary and secondary energy sources to fulfill the energy requirement in this century. High energy supply is required especially in the developing countries to sustain the lifestyle due to the growth in the world's population and techno-economic city. In fact, the sources of fossil fuel-based energy are limited and the use of fossil fuels can lead to the environmental pollution problem. Accordingly, the combustion of fossil fuels sources will give rise to the global warming issue, i.e., the greenhouse effect of carbon dioxide resulting in erratic weather patterns, such as floods, draughts, etc. In the last two decades, solar photovoltaic cells have been used as the alternatives to generate renewable, sustainable and green energy. High dye absorption rates, efficient charge separation of exciton, and free charge carrier formation as well as large area production at low costs contribute to the emerging photovoltaic technologies. Generally, the materials involved in photoanode section (acting as the platform for the electron collection) are the main key to produce high-efficiency photovoltaic cells. Currently, multijunction based solar panels showed the highest performance of 40% efficiency as compared to that of the conventional Si based solar panels with 22–27% efficiency. Apart of that, DSSCs sensitized by the silyl-anchor and carboxy-anchor dyes have attained the highest efficiency of 14%. In recent years, the metal doping or binary oxide photo-catalyst systems, particularly gra-phene-TiO 2 nanocomposites, have attracted much attention due to their extraordinary characteristics, i.e., (i) photocatalyst activity enhancement, and (ii) accelerated electron mobility to reduce the charge recombination. The high efficiency of the graphene-TiO 2 nanocomposites in DSSCs' reaction basically requires a suitable architecture that minimizes electron loss during excitation state and maximizes photon absorption. In order to further improve the immigration of photo-induced charge carriers during excitation state, considerable efforts have to be exerted to further improve the charge mobility and maximize the dye loading. It has also been reported that the properties of graphene-TiO 2 nanocomposites primarily depend on the nature of the preparation method, and the role of optimum dopants content incorporated into the graphene photoanode to improve the dye molecules loading and minimize the charge recombination. Therefore, we review recent achievements for different nanoarchitecture of TiO 2 , as well as graphene-TiO 2 composite nanostructured based photoanode in DSSCs performance with future prospects and challenges. Indeed, graphene-TiO 2 composite photoanode has proven to be of great interest for use in DSSCs.

Harvesting solar energy using photovoltaic (PV) cells is the most simple, efficient, and reliable approach to power marine electronics.  Installing PV above or under water provides cooling that increases power conversion efficiency and cleaning. Previous work quantified the performance of PV with different submerged environments and showed promising results in harvesting available underwater solar energy. These studies were limited to commercially-available silicon-based PV. Subsequent, theoretical studies point to enormous potential of using wide-band-gap PV in underwater conditions. With this motivation, for the first time, underwater measurements using dye-sensitized solar cells (DSSCs) employing wide-bandgap ruthenium sensitizers (1.8 eV) have been carried out here. The DSSCs were fabricated and characterized under submerged conditions up to 20 cm. Four replicates provided data detailing DSSCs potential for underwater PV applications when compared with the previously collected data for mono-crystalline, poly-crystalline and amorphous silicon PV. Although the light intensity under water decreases with an increase in depths, the rate of decrease in power output for DSSMs was only 40.68%, which was less than the traditional monocrystalline and polycrystalline silicon PV by approximately 20 to 25%. Also, compared to amorphous silicon PV, DSSCs showed a slightly better performance by 2-3%, which clearly displays the capability of DSSMs to harvest indirect/diffused lights in comparison to conventional Si/thin film PV. Compared to the conventional imported-semiconductor silicon-based PV, indigenously-fabricated DSSCs using locally-sourced materials showed tremendous relative increase in performance in underwater conditions. Further work is needed to optimize DSSCs to increase absolute PCE. Even given the studies limitations, it can be concluded that with the added advantages of simple fabrication process and cost-effectiveness, DSSMs have enormous future potential for underwater PV applications.

Bulk-heterojunction (BHJ) solar cells based on organic small molecules and polymers are the focus of increasing attention by science and commerce. In organic photovoltaic devices, a conjugated polymer layer is used as the donor, while a fullerene-based derivative is used as the acceptor. Poly(3,4-
ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is one of the most common interfacial materials used for organic BHJ solar cells. However, PEDOT:PSS is acidic and hygroscopic in nature, and it inherits microstructural inhomogeneities that cause not only gradual degradation, but a complete failure of BHJ solar cell devices. There is a growing interest in graphene-based solar cells because graphene-based materials offer ease of solution processability, high optical transparency, and high
power conversion efficiency. Graphene has been actively investigated for use as a transparent conducting electrode, and as a photoactive layer in fabricating solar cell devices. Power conversion efficiency in the range of 10% to 15% for graphene and inorganic semiconductor-based hybrid heterojunction solar cells, and 15.6% for graphene-containing perovskite solar cells has been observed. Organic materials-based solar cells degrade not only from environmental exposure, but also from
photo-oxidation caused by light illumination. In addition to higher power conversion efficiency, stability in graphene-based solar cells is critically important for commercial applications. In this review article, the stability of graphene-based heterojunction solar cells under atmospheric conditions is evaluated. Current studies show that the insertion of a graphene buffer layer into solar cell heterostructures stops
degradation and enhances stability in solar cell devices. Long-term environmental stability of graphenebased heterojunction solar cells for commercial applications is discussed.

A large proportion of the world population, especially the developing countries rely on the tradional system of medicines. The use of herbs in medicine is getting
popularized because of its natural origin with no or lesser side effects .Terminalia chebula is a moderate tree used in traditional medicines, Ayurveda, siddha and
unani. Studies conducted on Terminalia showed that it possess anti-bacterial, anti-cancerous, anti-fungal, anti-diabetic, anti-microbial, anti-mutagenic, antioxidant,
anti-ulcer, wound healing and anti- viral activity. It has also been found that it prevents the cardiac damage and also used for the treatment of kidney
disease. It is also found to be a mild, safe and efficacious laxative used in traditional medicine. It is also revealed that it is a safe compound and its constituents were
found to have therapeutic effect with no or very less toxicity. Terminalia chebula is also an active ingredient of a herbal formulation called as triphala which
comprises of three plants namely Emblica officinalis Gaertn. (Indian gooseberry), Terminalia bellerica Linn. (Bellerica myrobolan), Terminalia chebula Retz
(Chebulic myrobolan). This herbal preparation, triphala is used for the treatment of enlarged liver, stomach disorders, and for the pain in eyes. Medicinal plants
are the valuable and cheap source of therapeutic applications. This review encompasses the advantages of the above plant in terms of their pharmacological aspect.

Energy crisis is one of the most important issues in today's world. Conventional energy resources are limited and are one of the primary reason for environmental pollution. The use of renewable energy is becoming increasingly popular. Solar energy is rapidly gaining ground as an important mean of expanding renewable energy use. Solar tracking is employed in order to maximize solar radiation collection by a photovoltaic panel. In this paper we present the design, fabrication and testing of an active dual axis open loop solar tracking sensor. The compactness of the design facilitates its easy mounting on any surface or place exposed to solar irradiance. The solar irradiance is detected by an Organic Photovoltaic Cell (OPV) which scans the sky for the maximum power point. Different modes of operation have been accommodated in a single generic mode which stops operation at night and facilitates night return of the panel(s) the sensor is connected to. This system is independent with respect to geographical location of the solar panel and diurnal as well as seasonal variations. This sensor can be effectively employed in efficient solar energy extraction for systems of any scale. The operation of the system is independent with respect to the initial configuration and the starting conditions. The experimental testing shows agreement with true sun coordinates with satisfactory degree of accuracy. This work can be extended to reduce the scan time of the sensor.

Fabrication and characterization of different natural dyes extracts of dye sensitized solar cell (DSSC) are reviewed in this paper. Inorganic metal complex, N3 dye is also studied as a comparison. The paper focussed on the performance of sensitization
which is related to the interaction between dye and TiO2 surface. The electrical performances of the cell such as short circuit current density (JSC), open circuit voltage (VOC), fill factor (FF), and overall conversion efficiency (η) was also investigated via current-voltage characteristic measurement as well as light
absorption of dye loaded on TiO2 film. The resultant study showed that higher ratio of active compound and higher interaction of dye-TiO2 will results in higher conversion efficiencies.

We report the fabrication and testing of dye sensitized solar cells (DSSC) based on tin oxide (SnO 2) particles of average size ~20 nm. Fluorine-doped tin oxide (FTO) conducting glass substrates were treated with TiO x or TiCl 4 precursor solutions to create a blocking layer before tape casting the SnO 2 mesoporous anode. In addition, SnO 2 photoelectrodes were treated with the same precursor solutions to deposit a TiO 2 passivating layer covering the SnO 2 particles. We found that the modification enhances the short circuit current, open-circuit voltage and fill factor, leading to nearly 2-fold increase in power conversion efficiency, from 1.48% without any treatment, to 2.85% achieved with TiCl 4 treatment. The superior photovoltaic performance of the DSSCs assembled with modified photoanode is attributed to enhanced electron lifetime and suppression of electron recombination to the electrolyte, as confirmed by electrochemical impedance spectroscopy (EIS) carried out under dark condition. These results indicate that modification of the FTO and SnO 2 anode by titania can play a major role in maximizing the photo conversion efficiency.

Pure and Al-doped anatase TiO2 nanoparticles are prepared by an acid tailored sol-gel
method and successfully used as a photoanode for dye-sensitized solar cells (DSSCs). The samples
were characterized by using powder XRD, FE-SEM with EDX, UV-DRS, and Current-Voltage curve.
After Al doping, the conductivity of the TiO2 increases and it has a positive shift. The energyconversion
efficiency of a cell based on 0.05 mol% Al-doped TiO2 is significantly better, by about
4.6%, compared to that of a cell based on undoped TiO2. The synthesized Al-doped TiO2 material is
proven in detail to be a better photoanode material than pure TiO2 nanoparticles with a simple and
versatile way to prepare excellent photoanode materials.

Albeit photoelectrochemistry has been developed since several decades in thelast century, great impact in its everyday life application has been determinedjust in 1991 by Michael Grätzel and Brian O'Reagan through a revolutionaryapproach. Dye-sensitized solar cells (DSSCs), taking inspiration fromphotosynthesis, are currently one of the less expensive alternatives to normal photovoltaic devices based on silicon. Having reached a maximum overall efficiency of 15%, this new technology has been improved during the past 25 years toward mass production, industrial fabrication and improvements in performance.
Introduction of additional nanostructures inside the cells have been widely considered to enhance their efficiency, modifying either the absorption of the sensitizer either the conductivity of the semiconductor (i.e. TiO2) layer. Even though carbon and metal NPs-modified DSSCs have been successfully synthesized through modification of the TiO2 layer with gold nanoparticles, carbon nanotubes (single- and multi-walled) and derivatives of graphene, a small niche yet to explore is the interaction between the absorbing component, the dye, and these nanostructures.
For that reason, in the current study I aimed at characterizing the potential interactions of one of the most used sensitizers, Ruthenizer 535-bisTBA (i.e N719) with gold nanoparticles, SWCNTs and graphene oxide. The investigation has been developed studying the potential modification of the dye in a liquid suspension enriched with those nanostructures and the consequent modification after adsorption into the TiO2 layer. Finally, these results have been related to the performance of the final devices, which have been built as lab samples (active area ~ 1cm x 1cm).

The performance of dye sensitized solar cells (DSSCs), sensitized with natural pigments extracted from mango (mangifera indica), carica papaya, moringa oleifera leaves and bougainvillea flower was demonstrated. The photoactive electrodes of the various DSSCs were sensitized with aqueous extract of the natural pigments. The resulting photoelectrodes were successfully incorporated into the DSSCs. The photoelectrochemical perfomance of the DSSCs were evaluated under 100 mAcm-2 light intensity with open circuit voltage (V OC) ranging from 0.36 to 0.49 V and short circuit current density (J SC) ranging from 0.0134 to 0.1314 mAcm-2. From the photovoltaic performance of the extracts, the Mangifera Indica extract sensitized solar cell gave the best performance with J sc of 0.1314 mAcm-2 , V oc of 0.49 V, a fill factor (FF) of 0.59, and an overall solar energy conversion efficiency (η) of 0.038%. The sensitization performance related to the interaction between the dye and TiO 2 surface is discussed.

Dye-sensitized solar cells (DSSCs) are one type of highly efficient low-cost solar cells among third-generation photovoltaic devices. Replacing the expensive components of DSSCs with alternative inexpensive and earth-abundant materials would further reduce their price in the solar cell market. Recently, graphene-based low-cost counter electrodes (CEs) have been developed, which could serve as a potential alternative to the expensive platinum-based CEs. In this review article, we have summarized recent research on various reduced graphene oxide (rGO)-based composite CE materials, methods for their synthesis, their catalytic activity, and the effective utilization of such CEs in DSSCs. The photovoltaic performance of DSSCs made of rGO-based composite CEs were compared with the reference Pt-based cells, and the photovoltaic parameters are summarized in tables.

In this work, the vibrational characteristics of 2-Amino-6-Nitrobenzothiazole have been investigated. The structure of the molecule have been optimized by density functional theory B3LYP method with 6-311++G(d,p) basis set. The Raman and infrared spectra have been simulated from theoretically calculated intensities; also theoretical and experimental vibrational data confirms the presence of functional groups in the 2-Amino-6-Nitrobenzothiazole compound. UV-Visible spectrum of the title compound was recorded in the Ultra Visible region and the electronic absorption properties HOMO and LUMO energies were calculated by TD-DFT approach. Nonlinear optical properties were interpreted. The absorption bands are assigned to n→π* transitions. The results showed that 2-Amino-6-Nitrobenzothiazole may be a good candidate for Dye Sensitized Solar Cells (DSSC) applications.

ABSTRACT A vast array of colorants obtained from natural sources such as plants, insects/animals and microbes have been scrutinized in recent past for their use in different kinds of applications. Research into new natural dyes sources along with eco-friendly, robust and cost-effective technologies for their processing and application have greatly aided in widening the scope of natural dyes in various traditional and advanced application disciplines. This review encompasses a summary of research performed in last fifteen years (1998-2013) in different arenas of applications of natural dyes, with specific reference to technological development in natural textile dyeing and use of natural dyes in functional finishing of textiles, food coloration and dye sensitized solar cells. In addition, some newly discovered applications of natural dyes have also been discussed.

In this comprehensive study, the influence of titanium dioxide (TiO2) dopants decorated on Reduced Graphene Oxide (rGO) via spin coating technique as an efficient photoelectrode in DSSCs was investigated in detail. This study aims to determine the optimum spinning duration for decorating TiO2 onto rGO nanosheet photoanode for high DSSCs performance. The rGO nanosheet was prepared using the electrodeposition method. A dropped of 0.2 wt% of TiO2 solution was absorbed using micro-pipette (0.1 μl) and continuously applied on FTOrGO surface with the rate of 0.1 μl/5s. The spinning duration was varied from 10 to 50 s, and resultant samples were labelled as Lt, where t= 10, 20, 30, 40 and 50s, respectively. The experimental results showed that TiO2 decorated rGO nanosheet photoanode for 30s spinning duration exhibited a maximum power conversion efficiency of 9.98% than that of pure rGO nanosheet photoanode (4.74%) under 150 W of xenon irradiation, which is about 2.1 times improvement in DSSCs performance. Ti4+ ion was decorated onto rGO nanosheet leading to the highest interactions with the O-H functional group or Ti4+ could react with the epoxide or phenolic groups in rGO forming the Ti-O-C bonds.

Urchin-like SnO 2 microspheres have been grown for use as photoanodes in dye-sensitized solar cells (DSSCs). We observed that a thin layer coating of TiO 2 on urchin-like SnO 2 microsphere photoanodes greatly enhanced dye loading capability and light scattering ability, and achieved comparable solar cell performance even at half the thickness of a typical nanocrystalline TiO 2 photoanode. In addition, this photoanode only required attaching ~55% of the amount of dye for efficient light harvesting compared to one based on nanocrystalline TiO 2. Longer decay of transient photovoltage and higher charge recombination resistance evidenced from electrochemical impedance spectroscopy of the devices based on TiO 2 coated urchin-like SnO 2 revealed slower recombination rates of electrons as a result of the thin blocking layer of TiO 2 coated on urchin-like SnO 2. TiO 2 coated urchin-like SnO 2 showed the highest value (76.1 ms) of electron lifetime (τ) compared to 2.4 ms for bare urchin-like SnO 2 and 14.9 ms for nanocrystalline TiO 2. TiO 2 coated SnO 2 showed greatly enhanced open circuit voltage (V oc), short-circuit current density (J sc) and fill factor (FF) leading to a four-fold increase in efficiency increase compared to bare SnO 2. Although TiO 2 coated urchin-like SnO 2 showed slightly lower cell efficiency than nanocrystalline TiO 2 , it only used a half thickness of photoanode and saved ~45% of the amount of dye for efficient light harvesting compared to normal nanocrystalline TiO 2 .