Parameters determining efficiency and degradation of TiO2|dye|CuI solar cells

The influence of the micro-morphological structure of the TiO₂ film, the distribution of CuI in TiO₂ pores and the concentration of added surfactant in the CuI coating solution on the photocurrent of solid-state TiO₂|dye|CuI solar cells was examined by space resolved photocurrent imaging technique. Iodine is found to be competing with the oxidized dye molecules in accepting electrons from CuI and decreases the efficiency of the cell. TiO₂|dye|CuI cell degrade two hundred times faster than wet sensitization cells. This instability is considered to be due to the decomposition of the electron transfer-bridge between the sensitizer and CuI.     

Efficiency enhancement of solid‐state dye sensitized solar cell by in situ deposition of CuI

Solid‐state dye‐sensitized solar cells based on nanocrystalline TiO₂ thin film with the structures TiO₂/dye/CuI/Pt and TiO₂/dye/In situ CuI/CuI/Pt were developed in order to compare the use of In situ deposited CuI (In situ CuI). Porosity of the screen‐printed nanoporous TiO₂ thin film was enhanced by the addition of polystyrene balls. Evidence of decrease in interfacial resistance was observed by electrochemical impedance measurement for the device with In situ deposited CuI as compared to that without In situ deposited CuI as hole conductor. This was attributed to good interfacial contacts and better charge transfer between CuI and dye‐sensitized TiO₂ nanoparticles, which resulted in the enhancement of power conversion efficiency from 0.058 to 1.01%. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigation of the stability of solid-state dye-sensitized solar cells

The stability of the TiO₂/ruthenium dye/CuI solid-state solar cell was investigated under continuous simulated sunlight illumination. The cells showed fast degradation under full-spectrum sunlight illumination, but showed rather good stability when the ultraviolet part of the illumination was removed. XPS measurements showed evidence that TiO₂ could oxidize CuI in the presence of UV light. The photo-degradation mechanism of the cells is thus discussed on the basis of the photo-oxidative function of TiO₂. The long-term stability of the solid-state dye-sensitized solar cell (DSSC) was found to be improved under simulated sunlight by coating the TiO₂ porous electrode with an ultra-thin MgO layer, which was able to block the photo-oxidative activity of the TiO₂.     

Charge Generation in a Dye-Sensitized Solid-State Cell under Different Modes of Illumination

A dye-sensitized solid-state cell was fabricated by sandwiching ruthenium bypridyl complex in between porous TiO₂ and CuI films. Cis-dithiocyanate-bis(2,2′-bipyridyl -4-4′-dicarboxylate) ruthenium (II) exhibited excellent performance among the dyes tested for TiO₂∣dye∣CuI cell. Different mechanisms are proposed for charge generation of the cell under different modes of illumination. A high incident photon to current conversion efficiency was observed under back wall illumination compared to that of front wall illumination. Dye molecules exhibited a relay effect under back wall mode illumination at wavelengths shorter than 400 nm.     

Effect of organic dye on the performance of dye-sensitized solar cell utilizing TiO2 nanostructure films synthesized via CTAB-assisted liquid phase deposition technique

This work is concerned with the growth of TiO₂ nanostructures as photovoltaic materials of dyesensitized solar cell (DSSC) via phase liquid deposition technique treated with CTAB surfactant. This work investigates the influence of organic dyes, N719, N3 and Z907 as photosensitizer on the photovoltaic parameters of TiO₂ nanostructures dye-sensitized solar cells (DSSCs). It also highlights the effect of the concentration of the best dye, N719 on the performance of the cell. The platinum films as counter electrode of the DSSC were prepared by sputtering platinum pellet on ITO substrate. The redox couple of the electrolyte utilized in the DSSC was iodide/triiodide. The cell sensitized with N719 dye demonstrated the best performance compared with the cell sensitized with another two dyes, N3 and Z907. This is due to N719 dye possess the highest optical absorption in visible region. The cell sensitized with 0.8 mM N719 dye performs the highest short-circuit current density, J _sc and power conversion efficiency, η since it posses the highest absorption in visible region. The DSSC utilizing 0.8 mM N719 dye demonstrated the highest J _sc and η of 6.48 mA cm^?2 and 1.69%, respectively.     

Dye‐Sensitized TiO2 Nanotube Solar Cells: Rational Structural and Surface Engineering on TiO2 Nanotubes

Owing to well‐defined structural parameters and enhanced electronic properties, highly ordered TiO₂ nanotube arrays have been employed to substitute TiO₂ nanoparticles for use in dye‐sensitized solar cells. To further improve the performance of dye‐sensitized TiO₂ nanotube solar cells, efforts have been directed toward the optimization of TiO₂ photoanodes, dyes, electrolytes, and counter electrodes. Herein, we highlight recent progress in rational structural and surface engineering on anodic TiO₂ nanotube arrays and their effects on improving the power conversion efficiency of dye‐sensitized TiO₂ nanotube solar cells.     

A New Mussel‐Inspired Polydopamine Sensitizer for Dye‐Sensitized Solar Cells: Controlled Synthesis and Charge Transfer

The efficient electron injection by direct dye‐to‐TiO₂ charge transfer and strong adhesion of mussel‐inspired synthetic polydopamine (PDA) dyes with TiO₂ electrode is demonstrated. Spontaneous self‐polymerization of dopamine using dip‐coating (DC) and cyclic voltammetry (CV) in basic buffer solution were applied to TiO₂ layers under a nitrogen atmosphere, which offers a facile and reliable synthetic pathway to make the PDA dyes, PDA‐DC and PDA‐CV, with conformal surface and perform an efficient dye‐to‐TiO₂ charge transfer. Both synthetic methods led to excellent photovoltaic results and the PDA‐DC dye exhibited larger current density and efficiency values than those in the PDA‐CV dye. Under simulated AM 1.5 G solar light (100 mW cm^?2), a PDA‐DC dye exhibited a short circuit current density of 5.50 mW cm^?2, corresponding to an overall power conversion efficiency of 1.2 %, which is almost 10 times that of the dopamine dye‐sensitized solar cell. The PDA dyes showed strong adhesion with the nanocrystalline TiO₂ electrodes and the interface engineering of a dye‐adsorbed TiO₂ surface through the control of the coating methods, reaction times and solution concentration maximized the overall conversion efficiency, resulting in a remarkably high efficiency.     

Effects of Dye‐Adsorption Solvent on the Performances of the Dye‐Sensitized Solar Cells Based on Black Dye

The effects of the dye‐adsorption solvent on the performances of the dye‐sensitized solar cells (DSSCs) based on black dye have been investigated. The highest conversion efficiency (10.6 %) was obtained in the cases for which 1‐PrOH and the mixed solvent of EtOH and tBuOH (3:1 v/v) were employed as dye‐adsorption solvents. The optimized value for the dielectric constant of the dye‐adsorption solvent was found to be around 20. The DSSCs that used MeOH as a dye‐adsorption solvent showed inferior solar‐cell performance relative to the DSSCs that used EtOH, 1‐PrOH, 2‐PrOH, and 1‐BuOH. Photo‐ and electrochemical measurements of black dye both in solution and adsorbed onto the TiO₂ surface revealed that black dye aggregates at the TiO₂ surface during the adsorption process in the case for MeOH. Both the shorter electron lifetime in the TiO₂ photoelectrode and the greater resistance in the TiO₂–dye–elecrolyte interface, attributed to the dye aggregation at the TiO₂ surface, cause the decrease in the solar‐cell performance of the DSSC that used MeOH as a dye adsorption solvent.     

Stability of CdS-coated TiO<Subscript>2</Subscript> solar cells

The obstacle to realize the large-scale production of dye-sensitized solar cells (DSSCs) is its long-term stability and reliability problem. One of the main causes of the instability of DSSCs is the use of liquid electrolytes. In addition, exploring nano-sized particles of CdS as an alternative sensitizer for organic dye in dye-sensitized solar cells have attracted great interest due to the high cost and the instability of the organic dye. Our study has found that the CdS-coated TiO₂ cell degrades rapidly in the liquid electrolytes even under dark environment. In this work, a solid-state solar cell structure of Glass/FTO/TiO₂/CdS:Cu/FTO/glass was successfully made with an efficiency of 0.7%. CdS:Cu served as both the p-type conductor and absorber. No efficiency was obtained for cell structures of glass/FTO/TiO₂/CdS/FTO/glass. This indicates the effectiveness of hole conducting behavior of CdS:Cu. This is the first time that this type of solid-state solar cell is reported and improved stability is demonstrated.     

Improved efficiency of TiO2 nanotubes in dye sensitized solar cells by decoration with TiO2 nanoparticles

In the present work we investigate the effect of TiCl₄ treatments on the photoconversion efficiency of TiO₂ arrays used in dye sensitized solar cell. The results clearly show that by an appropriate treatment the decoration of the TiO₂ nanotube arrays with TiO₂ nanocrystallites of a typical size of 3 nm can be achieved. These particles can be converted to mixture of anatase and rutile phase by annealing in air. This decoration of the TiO₂ nanotubes leads to a significantly higher specific dye loading and, for certain annealing treatments, to a doubling of the solar cell efficiency (in our case from 1.9% to 3.8% of AM 1.5 conditions) can be achieved.     

Effect of Surface Protonation on Device Performance and Dye Stability of Dye-sensitized TiO2 Solar Cell

A flat thin TiO₂ film was employed as the photo-electrode of a dye sensitized solar cell (DSSC), on which only a geometrical mono-layer of dye was attached. The effect of sur-face protonation by HCl chemical treatment on the performance of DSSCs was studied. The results showed that the short-circuit current Jsc increased significantly upon the HCl treatment, while the open-circuit voltage Voc decreased slightly. Compared to the untreated DSSC, the Jsc and energy conversion efficiency was increased by 31% and 25%, respectively, for the 1 mol/L HCl treated cell. TiO₂ surface protonation improved electronic coupling between the chemisorbed dye and the TiO₂ surface, resulting in an enhanced electron in-jection. The decreased open-circuit voltage after TiO₂ surface protonation was mainly due to the TiO₂ conduction band edge downshift and was partially caused by increased electron recombination with the electrolyte. In situ Raman degradation study showed that the dye stability was improved after the TiO₂ surface protonation. The increased dye stability was contributed by the increased electron injection and electron back reaction with the electrolyte under the open-circuit condition.     

Oxide thickness and roughness factor as parameters for TiO<Subscript>2</Subscript>-dye sensitized solar cells performance

Oxide surface roughness in connection to oxide thickness has proved to be a key parameter for the performance of a dye sensitised solar cell. In this work, the numerical simulation of the system TiO₂-photo sensitive dye of a dye sensitized TiO₂ solar cell focuses on these two parameters. The steady-state numerical model used is based on the continuity and transport equations for charge species involved in the system, in connection to Poisson’s equation. Light absorbance is set dependent upon TiO₂ porosity and resulting electron density after illumination is derived as a function of the illuminating beam characteristics and material properties. Electron lifetime in the bulk is set dependent upon electron distribution with electron lifetime at the surface taking into consideration surface recombination. An effective dielectric constant dependent also upon the porosity of TiO₂ is used in the model. Results for different values of the TiO₂ thickness and surface roughness leading to optimum values for the cell performance are found in accordance with results reported in the literature.     

Energy Relay from an Unconventional Yellow Dye to CdS/CdSe Quantum Dots for Enhanced Solar Cell Performance

A new design for a quasi‐solid‐state Forster resonance energy transfer (FRET) enabled solar cell with unattached Lucifer yellow (LY) dye molecules as donors and CdS/CdSe quantum dots (QDs) tethered to titania (TiO₂) as acceptors is presented. The Forster radius is experimentally determined to be 5.29 nm. Sequential energy transfer from the LY dye to the QDs and electron transfer from the QDs to TiO₂ is followed by fluorescence quenching and electron lifetime studies. Cells with a donor–acceptor architecture (TiO₂/CdS/CdSe/ZnS‐LY/S^2?‐multi‐walled carbon nanotubes) show a maximum incident photon‐to‐current conversion efficiency of 53 % at 530 nm. This is the highest efficiency among Ru‐dye free FRET‐enabled quantum dot solar cells (QDSCs), and is much higher than the donor or acceptor‐only cells. The FRET‐enhanced solar cell performance over the majority of the visible spectrum paves the way to harnessing the untapped potential of the LY dye as an energy relay fluorophore for the entire gamut of dye sensitized, organic, or hybrid solar cells.     

Fabrication and performance of nanoporous TiO2/SnO2 electrodes with a half hollow sphere structure for dye sensitized solar cells

The incorporation of nano-crystalline semiconductors with novel kinds of ordered microstructure is a very important area of research in the field of dye sensitized solar cells. A sol–gel method involving hydrolysis of titanium isopropoxide was used to form TiO₂ nanoparticles on the surface of SiO₂ spheres. In this process, 1, 5, or 10 wt% of SnCl₂.2H₂O was added to the sol–gel solution. To prepare TiO₂/SnO₂ nanoparticles with a half hollow sphere structure, SiO₂ was removed with NaOH solution. The crystal phase, crystal shape, and surface properties of the metal oxide nanocrystals were studied by x-ray diffraction and scanning electron microscopy. The photovoltaic performance of the TiO₂/SnO₂ nanoparticles with half hollow sphere structures was measured. The dye sensitized solar cell using nanoporous TiO₂ as electrode materials exhibits an overall conversion efficiency of 7.36% with a light intensity of 100 mW/cm². The short circuit photocurrent (I_sc), open circuit photovoltage (V_oc), and conversion efficiency (η) of these solar cells were improved over conventional materials.     

Photocatalytic Reduction of Nitro Compounds Using TiO2 Photocatalyst by UV and Vis Dye-sensitized Systems

Nitro‐aromatic compounds can be photocatalytically reduced into the corresponding amine‐aromatic compounds using TiO₂ as a photocatalyst in the UV/TiO₂/holes scavenger and Vis/TiO₂/dye‐sensitized systems. In the UV/TiO₂/holes scavenger system, reaction substrate alcohols such as methanol could be used as the holes scavengers, and in the Vis/TiO₂/dye‐sensitized system, substrate alcohols could be oxidized to the corresponding aldehydes with high selectivity. When methanol was used as the holes scavengers and the illumination time was 6 h, 87.2% of p‐nitrotoluene could be photocatalytically reduced into p‐toluidine. In the Vis/TiO₂/dye‐sensitized system, the effect of aromatic alcohols for the photocatalytic reduction of nitrobenzene was better than that of other alcohols. At the same time, aromatic alcohols can be easily oxidized, and the production efficiencies of the corresponding aldehydes were higher than those of other alcohols. The possible reaction mechanisms were also proposed.     

Mapping of the Photoinduced Electron Traps in TiO2 by Picosecond X‐ray Absorption Spectroscopy

Titanium dioxide (TiO₂) is the most popular material for applications in solar‐energy conversion and photocatalysis, both of which rely on the creation, transport, and trapping of charges (holes and electrons). The nature and lifetime of electron traps at room temperature have so far not been elucidated. Herein, we use picosecond X‐ray absorption spectroscopy at the Ti K‐edge and the Ru L₃‐edge to address this issue for photoexcited bare and N719‐dye‐sensitized anatase and amorphous TiO₂ nanoparticles. Our results show that 100 ps after photoexcitation, the electrons are trapped deep in the defect‐rich surface shell in the case of anatase TiO₂, whereas they are inside the bulk in the case of amorphous TiO₂. In the case of dye‐sensitized anatase or amorphous TiO₂, the electrons are trapped at the outer surface. Only two traps were identified in all cases, with lifetimes in the range of nanoseconds to tens of nanoseconds.     

Solanum nigrum and Eclipta alba leaf pigments for dye sensitized solar cell applications

The dye sensitized solar cells have been assembled by using natural dye extracted from Solanum nigrum and Eclipta alba. The solar cell constructed using the S. nigrum sensitized TiO₂ photo-electrode exhibited a short-circuit photocurrent of 4.46 mA/cm² and a power conversion efficiency of 0.77 % and that of E. alba sensitized TiO₂ photo-electrode exhibited a short-circuit photocurrent of 4.04 mA/cm² and a power conversion efficiency of 0.60 %. S. nigrum gave better photosensitization effect than E. alba and presents the prospect to be used as an environment-friendly, low-cost alternative system.     

The influence of noncovalent interactions in metal‐free organic dye molecules to augment the efficiency of dye sensitized solar cells: A computational study

The efficiency of dye sensitized solar cells (DSSCs) can be enhanced with achieving better planarity of metal‐free organic dye molecules and thinning of their aggregation on the semiconductor surface. We report that the subtle noncovalent N^…S interaction between the substituted phosphazene group and thiophene spacer unit in dye molecule which induces the desired planarity and avoid aggregation of such molecules on the TiO₂ surface using DFT calculations. DFT results show that phosphazene group increases the maximum absorption wavelength (λ_max), driving force for electrons injection (ΔG_injection), singlet excited state lifetime (τ), dipole moments (μ_normal), and number of electrons transferred from dye to TiO₂ surface (Δq), which are known to augment the efficiency of DSSCs. Further, the lower ΔG_regeneration value of phosphazene containing dyes (e.g., –.37 eV, dye 2 ) than the reported dyes (e.g., –.81 eV, dye 1 ) indicate the faster electron injection rate from the former dye to the semiconductor TiO₂. The role of phosphazene group to prevent the aggregation of dye molecules on the TiO₂ anatase surface was also examined with GGA‐PBE/DNP level of theory. The calculated results suggest that the dye molecules on 1 ‐(TiO₂)₃₈ and 2 ‐(TiO₂)₃₈ anatase clusters avoids the aggregation due to the steric congestion induced by phosphazene group. This work reports to accomplish dual properties with subtle noncovalent interactions in dye molecules to augment the efficiency in DSSCs.     

TiO2 Nanoparticles Produced by Electric-Discharge-Nanofluid-Process as Photoelectrode of DSSC

Self-made TiO₂ nanoparticles were used as photoelectrode material of dye sensitized solar cell. The TiO₂ thin film coats through spreading nanoparticles evenly onto the ITO glass via self-made spin-heat platform, and then TiO₂ thin film is soaked in the dye N-719 more than 12 h to prepare the photoelectrode device. The TiO₂ nanoparticles produced by electric-discharge-nanofluid-process have premium anatase crystal property, and its diameter can be controlled within a range of 20-50 nm. The surface energy zeta potential of nanofluid is from -22 mV to -28.8 mV, it is a stable particle suspension in the deionized water. A trace of surfactant Triton X-100 put upon the surface of ITO glass can produce a uniform and dense TiO₂ thin film and heating up the spin platform to 200 oC is able to eliminate mixed surfac-tant. Self-made TiO₂ film presents excellent dye absorption performance and even doesn't need heat treatment procedure to enhance essential property. Results of energy analysis show the thicker film structure will increase the short-circuit current density that causes higher conversion efficiency. But, as the film structure is large and thick, both the open-circuit voltage and fill factor will decline gradually to lead bad efficiency of dye-sensitized solar cell.     

Electron Transport in Quasi‐Two‐Dimensional Porous Network of Titania Nanoparticles,Incorporating Electrical and Optical Advantages in Dye‐Sensitized Solar Cells

The integration of fast electron transport and large effective surface area is critical to attaining higher gains in the nanostructured photovoltaic devices. Here, we report facilitated electron transport in the quasi‐two‐dimensional (Q2D) porous TiO₂. Liquid electrolyte dye‐sensitized solar cells were prepared by utilizing photoanodes based on the Q2D porous substructures. Due to electron confinement in a microscale porous medium, directional diffusion toward collecting electrode is induced into the electron transport. Our measurements based on the photocurrent and photovoltage time‐of‐flight transients show that at higher Fermi levels, the electron diffusion coefficient in the Q2D porous TiO₂ is about one order of magnitude higher when compared with the conventional layer of porous TiO₂. The results show that microstructuring of the porous TiO₂ leads to an approximately threefold improvement in the electron diffusion length. Such a modification may considerably affects the electrical functionality of moderate or low performance dye‐sensitized solar cells for which the internal gain or collection efficiency is typically low.