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Carbon-based counter electrodes of dye-sensitized solar cells (DSSCs) such as carbon black-graphite composite (CB/Gr) have received unprecedented interest in recent years due to their ease of fabrication, good corrosion resistance, and low cost compared to platinum (Pt) electrodes. However, the poor surface adherence between the carbon counter electrodes (CE) and FTO substrate, low surface area, and poor inter-particle connection between the carbon materials have consistently become a major challenge. In order to overcome these issues, we have fabricated CB/Gr by incorporating binders of titanium (IV) isopropoxide (TTIP), and zirconium (IV) dioxide (ZrO2) as the counter electrodes for the DSSC. The performance of the CE is characterized by four-point probe conductivity measurement, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and current density voltage (J-V) characteristics. The results revealed that incorporating binders to the CB/Gr has improved the series resistance (RS) and charge transfer resistance (RCT), which enhances the short-circuit current density (JSC), fill factor (FF), and the power conversion efficiency (PCE) of the device. The TTIP binder in CB/Gr CE exhibited superior performance in DSSC is largely attributed to the formation of TiO2 in situ with small particle size of about 100 nm, leading to enhanced intimate contact between the carbon materials, high surface area, and better surface adherence between counter electrode and the FTO substrate. Our findings, thereby, offer the possibility to engineer and optimize the energy levels of CE in an effort to develop a high-performing DSSC counter electrode.

In this work, we investigate how Al and Mg doped mesoporous TiO2 layers can improve the power conversion efficiency (PCE) of perovskite solar cells (PSCs) with respect to undoped mesoporous TiO2. The PSC configuration used in this study consists of mesoscopic structure with CH3NH3PbI3 as the perovskite absorber. A PSC with optimized mol% of Al and Mg doped mesoporous TiO2 layers has been shown to achieve up to 22% higher efficiency than that of pure TiO2. While the Mg doping only enhances the open-circuit voltage (VOC), the Al doping effectively enhances the VOC, the short-circuit current density (JSC), and the fill factor (FF). The occupancy of the doped metals in the lattice is confirmed by XRD, EDX, and XPS. The Mg doping increases the band gap of TiO2 while the Al doping decreases it. The wide band gap in Mg doped TiO2 reduces the electron and hole recombination rate, thus increasing the JSC and VOC. By Al doping, deep trap sites in the TiO2 are eliminated, and this effectively reduces the recombination losses and in turn, increases the JSC. The enhanced electron-hole generation rate attributed to the decrease in the band gap of Al doped TiO2 also increases the JSC. In addition, there is an enhancement on the electron mobility by the presence of Al metal and this gives an increase in the FF. The results have demonstrated the possibility of improving the PCE of PSCs by fine tuning the band gap of mesoporous TiO2.

A dye-sensitized solar cell (DSSC) photocurrent efficiency (PCE) could be increased by 40.9% when the dye adsorbing TiO2 layer was introduced with reduced graphene oxide (rGO) layers. Thickness of rGO layer and number of rGO layers in the TiO2 anode were optimized. TiO2 and rGO were deposited on FTO substrate by electrophoretic deposition (EPD). The thickness of the rGO containing TiO2 anode was kept constant (10–11 μm) at all the times. Three rGO layers containing TiO2 anode has shown the highest PCE of 6.2%. rGO incorporation improved electron transfer that countered recombination losses hence increasing photocurrent density (JSC) of the DSSC.

We have computationally designed and characterized a series of new organic D−π−A architected dyes that have originated from cyanidin, which is vastly available in nature, for effective sensitization of DSSCs with absorption spectra extending up to near infrared region. Cyanidin acts as the donor group while cyanoacrylic acid and thieno [3, 2-b] thiophene are employed as the acceptor and π-spacer, respectively. Sensitization performance, depending on the substituted position of the π-spacer-acceptor (π-A) combination on cyanidin molecule, is examined by the results of density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. The calculated data of free energy change driving force ( Δ G inject ), electron regeneration driving force ( Δ G regen ), open circuit potential eV OC and light harvesting efficiency (LHE) suggest two preferred substitutions of π-A combination to cyanidin molecule that leads to an efficient DSSC. At LUMO the designed sensitizers have denser electron cloud towards acceptor group that leads to an efficient electron injection process. All π-A substitutions resulted a broader absorption spectrum with a redshift up to 2500 nm which is a significant improvement compared to the vast majority of reported sensitizers.

Although efficiency of Dye Sensitized Solar Cell (DSSC) is still below the performance level of the market dominance silicon solar cells, in the last two decades DSSC has gathered sufficient interests because of the simplicity in device fabrication and low material cost, and therefore, DSSC is providing a possibility of solar cells production at a low entry cost. This review presents the research progress made in the implementation of natural pigments in DSSC. These pigments function as dye sensitizers and they play a major role in DSSC by absorbing light, and supplying electrons to the semiconductor matrixes in the cell. The common choices of dyes are the metal complexes, organic and/or natural dyes. A better efficiency with higher durability is observed for DSSC using metal complexes and organic dyes, however, the process of synthesizing these dyes is laborious, costly, and involves the use of toxic materials. As an alternative, natural pigments (dyes) found in plants such as anthocyanin, carotenoid, aurone, chlorophyll, tannin, betalain and many others are accepted as dyes in DSSCs. These natural pigments are easily obtained from fruits, flowers, leaves, seeds, barks and various parts of plants. Despite the limited performance of natural dyes, the prevailing advantages of natural dyes include high absorption coefficients, high light harvesting efficiency, low cost extraction and low toxicity. This review provides insight into the usage of the various natural pigments as sensitizers, the techniques to improve the pigments performance in DSSC, an outlook on the developmental work on the application of natural pigments in DSSC and their limitation. Additionally, the paper discusses the overall operation principle and the recent developments of each component of DSSC, as well as, comparing the material cost between natural dye and synthetic dye DSSC.

Doping is a method whereby small amounts of impurities are introduced into the lattice of a material and is employed for improving the efficiency of dye-sensitized solar cells (DSSCs) via modification of the semiconductor material. Co-doping, which involves doping with more than one type of impurity, is typically used over doping owing to its unique effects on the short-circuit current and open-circuit voltage; the different types of added impurities can exert a synergy effect in enhancing the performance of DSSCs. Of particular interest is the study of the effects of the ionic radii of co-dopants on the performance of DSSCs that is not well understood to date. Thus, in this paper, TiO 2 was co-doped with lanthanum and magnesium, calcium, or aluminium at respective contents of 0.5 mol%. The co-doped TiO 2 and pure TiO 2 powders were prepared by sol–gel. Mg-La co-doped TiO 2 -based DSSC displayed the highest efficiency ( i.e. , 6.60%) and Al-La co-doped TiO 2 -based DSSC displayed the lowest efficiency. Among the dopants studied herein, aluminium ion has the smallest ionic radius. Thus, aluminium ions could easily enter the lattice structure of TiO 2 , generating a high concentration of holes that led to the decrease of electron transport and photocurrent, hence lower DSSC efficiency.

ZnO@TiO2 core–shell nanostructures have been manipulated with metal ion dopants to create DSSC photoanodes with reduced charge transfer recombination. ZnO and TiO2 were modified by doping with Cd and Mg, respectively, resulting in a reduction in the band-gap for Cd:ZnO and an increase in the band-gap for Mg:TiO2. A series of core–shell nanostructures based on a ZnO or a Cd:ZnO core and TiO2 or a Mg:TiO2 shell have been investigated as DSSC photoanodes. In another series, the core–shell materials were reversed for complete evaluation of our hypothesis. The structures of the core–shell nanoparticles, optoelectronic and interfacial charge transfer of the DSSCs were analyzed by XRD, SEM, TEM, XPS, Mott-Schottky experiment, UV–vis DRS, J–V and EIS measurements. The power conversion efficiencies (PCEs) of DSSCs based on these core–shell structures were observed to depend on the flat band of the shell oxide relative to that of the core oxide. DSSCs with Cd:ZnO@Mg:TiO2 and Cd:ZnO@TiO2 photoanodes achieved Voc and FF values comparable to those of DSSCs with TiO2 anodes. A moderate energy gradient and high potential barrier in these core–shell structures resulted in longer effective electron lifetimes and lower electron recombination in the corresponding DSSCs. The low PCE registered for DSSCs with anodes of Cd:ZnO@Mg:TiO2 and Cd:ZnO@TiO2 were attributed to the presence of a high proportion of rutile phase, caused by sintering at 650 °C and lower dye adsorption as a result larger particle sizes caused by Cd doping.

Natural dyes from Ixora coccinea (RX) and Bougainvillea sp. (BG) were extracted and these individual dyes as well as the cocktail dye of RX and BG (1:1 v/v ratio) were investigated as dye sensitizers in dye sensitized solar cells (DSSCs). To analyze the capability of the dyes, various characterization methods were deployed such as incident photon-to-current efficiency (IPCE), current-to-voltage (I-V) characteristics, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that DSSC sensitized with RX performed the best with η = 0.76%, followed by the cocktail dye (η = 0.40%) and BG (η = 0.21%). This best overall performance of RX was attributed to the charge transport resistance (Rtr = 3.89 Ω), with the highest electron density (ɳs = 9.45 × 1028) and effective diffusion coefficient (Deff = 2.43 × 10− 8 m2/s), which accounted for high Jsc. Co-dominance performance of DSSC sensitized with cocktail dye was observed where the cocktail dye has demonstrated an improved Voc as compared to RX and improved Jsc against BG, suggesting individual influence from both dyes.

An innovative type of composite photoanode consisting of a TiO 2 nanofibre (NF) layer sandwiched between two TiO 2 nanoparticle (NP) layers has been fabricated and tested in dye sensitized solar cells. After sintering, the nanofibres in the layer have turned to an elongated bead type nanostructure. DSSCs fabricated with the TiO 2 NP/NF/NP composite three layer photoanode sensitized with N 719 Ruthenium dye and a electrolyte solution consisting of tetrapropylammonium iodide and iodine dissolved in acetontrile and ethylene carbonate co-solvent showed the highest efficiency of 7.09% where as the DSSC with TiO 2 nano particle photoanode and the same electrolyte showed an efficiency of 5.38%. The increased efficiency has been attributed to enhanced light harvesting due to scattering within the TiO 2 nanofibre structure. The efficiency of the highest efficiency DSSC has been further enhanced by using the “mixed cation effect” where the single iodide salt, Pr 4 NI, in the electrolyte has been replaced by two iodide salts KI and Pr 4 NI resulting an efficiency of 8.80%. The combined use of the TiO 2 three layer composite photoanode and the mixed cation iodide salt containing electrolyte represents an impressive efficiency enhancement by 64% compared to a corresponding DSSC made with TiO 2 nanoparticle (NP) photoanode and an electrolyte with the single iodide salt Pr 4 NI.

The effect of Lanthanum ions (La3+) on charge trapping in dye-sensitized solar cell (DSSC) photoanodes has been investigated with doped and surface-treated TiO2 nanoparticles. Doped nanoparticles consisting of 0.5 mol.% Mg and La co-doped TiO2, 0.5 mol.% Mg doped TiO2 and pure TiO2 were synthesized by the sol gel method. Surface-treated nanoparticles of Mg doped TiO2 and pure TiO2 were prepared by ball milling in 0.05 M aqueous La3+ solution. All materials were analyzed by XRD, XPS and UV–Vis DRS. Cell performance, surface free energy state changes and electron injection efficiency of DSSCs based on these nanoparticles were evaluated using current –voltage measurements, EIS and Incident photon to current conversion efficiency. Doped materials had La and Mg ions incorporated into the TiO2 lattice, while no lattice changes were observed for the surface-treated materials. Less visible light was absorbed by treated oxides compared with doped oxide samples. The overall power conversion efficiencies (PCE) of DSSC photoanodes based on doped materials were twice those of photoanodes fabricated from treated nanoparticles. Doping establishes deep traps that reduce the recombination of electron–hole (e–h) pairs. Conversely, the presence of absorbed oxygen in treated materials enhances e–h recombination with electrolyte at surface trap sites.

In this work, we have investigated the performance of acetylene carbon black/graphite (AB/G) composite counter electrodes (CEs) by incorporating TiO2 as a binder in dye-sensitized solar cells (DSSCs). We obtained five types of composite CE films at different weight ratios of 0:1, 1:3, 1:1, 3:1 and 1:0 by adding a constant amount of TiO2 to a mixture of AB/G. The performance of the composite electrodes was assessed by using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopies and photocurrent density–voltage characteristics. The results have shown enhanced DSSC efficiency due to improved charge transfer properties of the CE when adding TiO2. TiO2 enhances the binding of the electrode to the substrate. AB/G/TiO2 composites show superior overall results compared to AB/TiO2 and G/TiO2. Since AB has high catalytic activity and surface area, as the AB content of the composite is increased, the electrochemical properties of the CEs are improved. The DSSC with AB:G (3:1) exhibited the maximum power conversion efficiency (PCE) of 5.9% with the highest fill factor (FF) of 0.55, which are comparable to those DSSCs employing platinum CEs with PCE of 6.2% and FF of 0.67.

TiO 2 is a technologically important, naturally occurring, low cost material used in energy, environmental, health and many other applications. This paper reports the possibility of using commercial TiO 2 in several different applications. The efficiency of a silver nanoparticle incorporated TiO 2 dye sensitized solar cell increased by 27% evidently due to the plasmonic effect. In a dye sensitized solar cell when nanopowder TiO 2 photoanode was replaced by a composite TiO 2 photoanode containing TiO 2 nanopowder and TiO 2 nanofibres, the cell efficiency enhanced by more than 30%. In an electrochromic device of configuration, FTO glass/TiO 2 /Poly (methylmethacrylate) electrolyte/SnO 2 /FTO glass, an impressive reversible colour change was observed. Mg rechargeable battery fabricated with a TiO 2 cathode exhibited a discharge capacity of 220 mAh g -1 showing that Mg ++ can be reversibly intercalated in to the TiO 2 structure. An electrospun nanofibre membrane prepared from a biodegradable polymer and functionalized with TiO 2 nano powder was capable of removing arsenic (As) from drinking water efficiently.

An improvement in the efficiency of Ixora ( Ixora sp. (Rubiaceae)) floral dye sensitized solar cells (DSSCs) has been achieved by diminishing the pigment’s interactions. Liquid column chromatography (LCC) separated the dye components, namely aurone, pelargonidin, and derivatives of cyanidin & malvidin, showed improved photovoltaic performance when compared to cells sensitized by the original dye extract of Ixora. The LCC separated dye components were analyzed using UV–Vis, fluorescence and Fourier transform infrared (FTIR) spectroscopic studies. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and band gaps of the dyes were investigated. The DSSC prepared with the LCC separated dye showed energy conversion efficiencies (ECEs) ranging from 0.203% to 0.951%, whereas the original Ixora dye sensitized cell showed an ECE of 0.381%. Transient photovoltage (TPV) measurements and electrochemical impedance spectroscopy (EIS) were used to elucidate the photovoltaic parameters.

This paper describes a double layered co-sensitization in dye sensitized solar cells (DSSCs) by using natural pigments from Ixora flower (Ixora sp. (Rubiaceae)) and the outer dark purple skin of ‘Kembayau’ (Canarium odontophyllum) fruit. UV–vis absorption data revealed that both dyes were anthocyanins. Co-sensitization was done by first adsorbing the dye from C. odontophyllum into TiO2 electrode by dipping, and then by removing adsorbed dye of the top layer of TiO2 using a de-sorption solution before the Ixora sp. dye was allowed to adsorb. Power conversion efficiency of the co-sensitized solar cell was 1.55%. The conversion efficiencies of DSSCs sensitized with Ixora sp. , C. odontophyllum and the mixture of both dyes (1:1) were 0.96%, 0.59% and 1.13% respectively. The superior conversion efficiency achieved by layered co-sensitization is attributed to the high adsorption capacities of Ixora sp. and C. odontophyllum, and the homogeneous monolayer adsorption of Ixora sp. as revealed by Freundlich and Langmuir adsorption isotherms.

The active constituents of Canarium odontophyllum (COP) were investigated experimentally and theoretically for dye sensitized solar cell (DSSC) application. Three main flavonoid pigments (cyanidin, pelargonidin and maritimein) were detected in COP showing photo-energy conversion efficiencies of 1.43%, 0.87% and 0.60%, respectively. The molecular geometries, electronic structures, optical absorption spectra and proton affinity of these molecules were investigated with DFT/TDDFT. All three molecules displayed π→π * transition dominant in HOMO→LUMO transition. The anchoring groups onto TiO 2 surface were deduced from combined experimental and calculated data. All the constituents of COP are potential sensitizers for DSSC.