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A series of arylamine-free organic dyes that have a pyrenoimidazole donor, a cyanoacrylic acid acceptor, and different π-linkers were synthesized and characterized by optical, electrochemical, and theoretical investigations. The nature of the π-spacer exerts a significant effect on electronic properties of these dyes. The absorption maxima red-shifts on progressive addition of thiophene units in the conjugation pathway. All the dyes displayed negative solvatochromism indicative of effective solvation of the dyes by polar solvents in the ground state. The oxidation potential of the dyes shifted negatively on introduction of electron rich spacer. TDDFT computations were also performed to explain the optical and electrochemical properties of the dyes. They were demonstrated as sensitizers in dye-sensitized solar cells, the efficiency of which is promising.

Mesoporous TiO2 spheres (hereafter, MSs) were synthesized and incorporated into the photoanode of a quasi-solid state dye-sensitized solar cell (QSS-DSSC) containing an air stable ionic liquid electrolyte, namely 1-propyl-3-methylimidazolium iodide (PMII) along with triethylmethylammonium methyl sulfate (TEMAMS) (65 : 35 = v/v), in order to improve its performance. The presence of large pores in the MS, as confirmed using a high resolution scanning electron microscope (HR-SEM) and a mercury porosimeter, facilitates the penetration of QSS-electrolytes into the thin film, whereas their high surface area (108.1 m2 g−1) helps for high dye loading. Further, the large particle size increases the scattering ability of incident light leading to an excellent increment in the number of photons. The performance of DSSCs containing bi-ionic liquid (bi-IL) based electrolytes, namely, PMII/TEMAMS and PMII/1-ethyl-3-methylimidazolium tetrafluoborate (EMIBF4), with the addition of 0.2 M iodine, 0.4 M N-methylbenzimidazole (NMBI), and 0.15 M guanidiniumthiocyanate (GuSCN), was compared, where the DSSC based on PMII/TEMAMS bi-ILs demonstrates superior efficiency (6.18%) than that of PMII/EMIBF4 based one (4.53%). The DSSC with PMII/TEMAMS shows extraordinary durability and unfailing stability for 1200 h even though it was stored in the dark at 50 °C. Further, the PMII/TEMAMS bi-IL electrolyte shows a gel-state at room temperature naturally without adding any gelators or polymers.

Efficient titanium nitride/titanium oxide (TiN/TiO2) composite photoanodes have been proposed for the use not only in dye-sensitized solar cells (DSSCs) but also for water splitting. When the TiN precursor films were sintered at 500 °C for 0.5 to 4 h, they were partially converted to crystalline TiO2 containing both rutile and anatase phases. For the DSSCs, higher TiN content in the photoanodes resulted in a more negative flat-band potential and higher conductivity but lower surface area for the dye adsorption; therefore, the increase in VOC and FF but the decrease in JSC value were observed. The best DSSC, with TiN/TiO2 composite photoanode annealed for 1 h, exhibited a power conversion efficiency of 7.27%, while the cell without TiN, i.e., the cell with a standard P25 photoanode, showed an efficiency of 7.02%. For the water splitting, higher TiN content in the photoanodes resulted in better triggering of the H2O electrolysis, but less photo-induced current response at UV light illumination. Considering the water splitting performance measured at AM 1.5G, the TiN/TiO2 composite photoanode annealed for 1 h showed the best photo-induced current density (Jpho) of 0.12 mA cm−2, as compared with that of the standard P25 film. With the TiN/TiO2 composite photoanode annealed for 1 h, both DSSCs and water splitting electrochemical devices achieved their best performance independently.

Dye-sensitized solar cells (DSSCs) are fabricated using low-cost materials and a simple fabrication process; these advantages make them attractive candidates for research on next generation solar cells. In this type of solar cell, dye-sensitized metal oxide electrodes play an important role for achieving high performance since the porous metal oxide films provide large specific surface area for dye loading and the dye molecule possesses broad absorption covering the visible region or even part of the near-infrared (NIR). Recently, metal-free sensitizers have made great progress and become the most potential alternatives. This review mainly focuses on recent progress in metal-free sensitizers for applications in DSSCs. Besides, we also briefly report DSSCs with near-infrared (NIR) organic sensitizers, which provide the possibility to extend the absorption threshold of the sensitizers in the NIR region. Finally, special consideration has been paid to panchromatic engineering, co-sensitization, a key technique to achieve whole light absorption for improving the performance of DSSCs.

Dye-sensitized solar cells (DSSCs) have been extensively investigated as a potential renewable power source because they do not rely on expensive or energy-intensive processing methods. Within a DSSC, the electrolyte is very important as it provides the ionic conductivity for charge transport between the photoanode and the cathode, as well as sets the potential barrier necessary for energy conversion. Considering the durability of DSSCs in practical applications, ionic liquids (ILs) have become the most promising electrolyte materials due to their advantages of negligible vapor pressure, high thermal stability, wide electrochemical window, and high ionic conductivity. Recently, great progress has been made in the development of solid-state ILs to avoid the fluidity and potential leakage of IL-based electrolytes during long-term operation under solar light illumination. This chapter reviews some of the key research on the topic of solid-state ILs using polymeric ILs or IL crystals for DSSCs, and some of the relevant literature has also been briefly introduced.

In this study, we report a novel, one-step synthesis method to fabricate multilayer graphene (MLG)-wrapped copper nanoparticles (CuNPs) directly on various substrates (e.g., polyimide film (PI), carbon cloth (CC), or Si wafer (Si)). The electrical resistivities of the pristine MLG-CuNPs/PI and MLG-CuNPs/Si were measured 1.7 × 10–6 and 1.4 × 10–6 Ω·m, respectively, of which both values are ∼100-fold lower than earlier reports. The MLG shell could remarkably prevent the Cu nanocore from serious damages after MLG-CuNPs being exposed to various harsh conditions. Both MLG-CuNPs/PI and MLG-CuNPs/Si retained almost their conductivities after ambient annealing at 150 °C. Furthermore, the flexible MLG-CuNPs/PI exhibits excellent mechanical durability after 1000 bending cycles. We also demonstrate that the MLG-CuNPs/PI can be used as promising source-drain electrodes in fabricating flexible graphene-based field-effect transistor (G-FET) devices. Finally, the MLG-CuNPs/CC was shown to possess high performance and du...

As a new class of non-volatile memory, resistive random access memory (RRAM) offers not only superior electronic characteristics, but also advanced functionalities, such as transparency and radiation hardness. However, the environmental tolerance of RRAM is material-dependent, and therefore the materials used must be chosen carefully in order to avoid instabilities and performance degradation caused by the detrimental effects arising from environmental gases and ionizing radiation. In this work, we demonstrate that AlN-based RRAM displays excellent performance and environmental stability, with no significant degradation to the resistance ratio over a 100-cycle endurance test. Moreover, transparent RRAM (TRRAM) based on AlN also performs reliably under four different harsh environmental conditions and 2 MeV proton irradiation fluences, ranging from 1011 to 1015 cm−2. These findings not only provide a guideline for TRRAM design, but also demonstrate the promising applicability of AlN TRRAM for future transparent harsh electronics.

In the last two decades, dye-sensitized solar cells (DSSCs) have attracted more attention as an efficient alternative to economical photovoltaic devices, and the highest efficiency record has increased from ∼7% to ∼14%. To be more competitive in the solar cell markets, various organic materials are investigated and used in DSSCs to improve the cell efficiency, enhance the cell durability, and reduce the cost of production. In this review article, we provide a short review on the organic materials used for the preparation of photoanodes (including metal element-free organic dye sensitizers), quasi/all-solid-state electrolytes, and metal element-free electrocatalytic films in DSSCs with the cell efficiencies of >5%. Finally, the future perspectives for DSSCs are also briefly discussed.

Organic dyes containing 2-diphenylaminocarbazole donors and decorated with auxiliary chromophores at the diphenylamine moiety have been synthesized and characterized. The nature of the chromophores on diphenylamine unit alters the light-harvesting properties and HOMO/LUMO energies of the dyes. Butoxy substitution raises the HOMO and lowers the LUMO energies. But the incorporation of fluorenyl units fine-tunes the LUMO upwardly, which improves the thermodynamic driving force for electron injection into the conduction band of TiO2 and hikes the incident photon-to-current conversion efficiency. Consequently, a dye with fluorene in the donor unit and thiophene in the π-conjugation pathway is the most efficient (5.76 %) and has the highest photocurrent density (14.60 mA cm−2) in the series. Electrochemical impedance analysis of the devices showed the importance of fluorene units in suppressing electron recombination.

Nitrogen-doped graphene (NGR) was utilized in dye-sensitized solar cells for energy harvesting. NGR on a Pt-sputtered fluorine-doped tin oxide substrate (NGR/Pt/FTO) as counter electrodes (CEs) achieves the high efficiency of 9.38% via the nitrogen doping into graphene. This is due to (i) the hole-cascading transport at the interface of electrolyte/CEs via controlling the valence band maximum of NGR located between the redox potential of the I–/I– redox couple and the Fermi level of Pt by nitrogen doping, (ii) the extended electron transfer surface effect provided by large-surface-area NGR, (iii) the high charge transfer efficiency due to superior catalytic characteristics of NGR via nitrogen doping, and (iv) the superior light-reflection effect of NGR/Pt/FTO CEs, facilitating the electron transfer from CEs to I3– ions of the electrolyte and light absorption of dye. The result demonstrated that the NGR/Pt hybrid structure is promising in the catalysis field.

As the catalytic material for the counter electrode (CE) of a dye-sensitized solar cell (DSSC), a composite film of nickel nanoparticles (Ni-NPs) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was deposited on an FTO glass substrate, by using a home-made polymeric dispersant, poly(oxyethylene)-segmented imide (POEM). Scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectroscopy (EDX) were used to characterize the films. A solar-to-electricity conversion efficiency (η) of 7.81% was achieved for the DSSC using Ni-NPs/PEDOT: PSS, while the DSSC with the Pt CE showed a ηof 7.63%. The best composite film showed a high stability, when it was subjected to potential cycling for 100 cycles in an electrolyte containing the redox couple, iodide/triiodide (I-/I3−), while the Pt film showed a considerable decrease in its stability. In replacing the conventional sputtered Pt film as the CE in a DSSC, the Ni-NPs/PEDOT: PSS film exhibited multiple advantages of higher power conversion efficiency, higher stability of the catalytic film, and less expensive material cost. The photovoltaic parameters of the cells were substantiated by incident photon-to-current conversion efficiency (IPCE) spectra, electrochemical impedance spectroscopy (EIS), Tafel polarization plots, and cyclic voltammetry (CV).

A novel polymeric ionic liquid (PIL), poly(oxyethylene)-imide-imidazole complex coupled with iodide anions (coded as POEI-II), was synthesized for preparing the gel electrolyte for quasi-solid-state dye-sensitized solar cells (QSS-DSSCs). Herein, POEI-II, which acts simultaneously as a redox mediator in the electrolyte and a polymer for the gelation of an organic solvent-based electrolyte, was used to improve cell durability. In the structure of POEI-II, the presence of the POE segment can chelate lithium cations (Li+) within the electrolyte to improve the open-circuit voltage (VOC) of a QSS-DSSC, and enable a strong dipole–dipole lone-pair electron interaction with iodide ions (I−) of electrolyte composition rendering the high ionic conductivity and the diffusivity of a redox couple within the gel electrolyte. Consequently, the QSS-DSSC with the POEI-II gel electrolyte reaches a high cell efficiency of 7.19%. In addition, 5 wt% of multi-wall carbon nanotubes (MWCNTs) are incorporated into the POEI-II gel electrolyte as the extended electron transfer material (EETM) to facilitate charge transfer from the counter electrode to the redox mediator, which benefits the dye regeneration more efficiently. Meanwhile, the POE segments in POEI-II can prevent the MWCNTs from aggregation, which makes the well dispersed MWCNTs largely exposed to redox mediators. The highest cell efficiency of 7.65% was achieved by using the POEI-II/MWCNT gel electrolyte and it showed an unfailing durability of greater than 1000 h under 50 °C. This properly designed PIL paves a promising way for developing highly efficient and durable QSS-DSSCs.

Composite films of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with various functional ionic liquids were obtained by electro-polymerization process on indium-doped tin oxide (ITO) conducting glasses. The ITO glasses coated with the composite films were used as the counter electrodes in dye-sensitized solar cells (DSSCs). Various imidazolium cations with different alkyl chains (–C2H5, –C6H13, –C10H21) and anions ( BF 4 − , PF 6 − , SO 3 CF 3 − , TFSI − ) were used as the ionic liquids. The films of PEDOT doped with the ionic liquids render for their DSSCs enhanced power conversion efficiencies (η), compared to that of the cell with bare PEDOT counter electrode. The DSSC with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMITFSI)-doped PEDOT counter electrode shows a high η of 8.87±0.11, while the DSSCs with bare PEDOT and platinum counter electrodes show the ηs of 6.19±0.09 and 8.09±0.06, respectively. X-ray photoelectron spectroscopy, scanning electron microscopy, and contact angle data were used to characterize the ionic liquid-doped PEDOT films. Cyclic voltammetry, rotating disk electrode, Tafel polarization plots, electrochemical impedance spectroscopy, and incident photon-to-current conversion efficiency curves were used to substantiate the photovoltaic performance.

A series of new organic dyes containing an electron-deficient diphenylquinoxaline moiety was synthesized and employed as the photosensitizers in dye-sensitized solar cells (DSSCs). The multiple phenyl rings in the peripheral positions of the dye structure provide a hydrophobic barrier to slow down the charge recombination. The photophysical and electrochemical properties of these dyes were investigated in detail. The cell performance and the associated photophysical and electrochemical properties can be easily tuned by the modification of the aromatic fragments within the π spacer. Dye CR204-based DSSC reached the best energy conversion efficiency of 6.49% with an open-circuit voltage of 666 mV, a short-circuit photocurrent density of 14.9 mA cm−2, and a fill factor of 0.66. The IPCE of CR204-based DSSC covers the light-harvesting to NIR region.

The high performances of dye-sensitized solar cells (DSSCs) based on seven new dyes are disclosed. Herein, the synthesis and electrochemical and photophysical properties of a series of intentionally designed dipolar organic dyes and their application in DSSCs are reported. The molecular structures of the seven organic dyes are composed of a triphenylamine group as an electron donor, a cyanoacrylic acid as an electron acceptor, and an electron-deficient diphenylquinoxaline moiety integrated in the π-conjugated spacer between the electron donor and acceptor moieties. The DSSCs based on the dye DJ104 gave the best overall cell performance of 8.06 %; the efficiency of the DSSC based on the standard N719 dye under the same experimental conditions was 8.82 %. The spectral coverage of incident photon-to-electron conversion efficiencies extends to the onset at the near-infrared region due to strong internal charge-transfer transition as well as the effect of electron-deficient diphenylquinoxaline to lower the energy gap in these organic dyes. A combined tetraphenyl segment as a hydrophobic barrier in these organic dyes effectively slows down the charge recombination from TiO2 to the electrolyte and boosts the photovoltage, comparable to their Ru(II) counterparts. Detailed spectroscopic studies have revealed the dye structure-cell performance correlations, to allow future design of efficient light-harvesting organic dyes.

New organic dyes containing fluorene functionalized with two imidazole chromophores as donors and cyanoacrylic acid acceptors have been synthesized and successfully demonstrated as sensitizers in nanocrystalline TiO2-based dye-sensitized solar cells (DSSCs). The monoimidazole analogues were also synthesized for comparison. The Sommelet reaction of bromomethylated 2-bromo-9,9-diethyl-9H-fluorene produced the key precursor 7-bromo-9,9-diethyl-9H-fluorene-2,4-dicarbaldehyde required for the preparation of imidazole-functionalized fluorenes. Since the dyes possess weak donor segment, the electron-richness of the conjugation pathway dictated the optical, electrochemical, and photovoltaic properties of the dyes. The dyes served as sensitizers in DSSC and exhibited moderate efficiency up to 3.44%. The additional imidazole present on the fluorene has been found to retard the electron recombination due to the bulkier hydrophobic environment and led to high open-circuit voltage in the devices.

A series of new metal free organic dyes containing carbazole as donor and π-linker have been synthesized and characterized as effective sensitizers for dye sensitized solar cells (DSSCs). The carbazole functionalized at C-2 and C-7 served as electron-rich bridge. The donor property of the carbazole is substantially enhanced on introduction of tert-butyl groups at C-3 and C-6 positions and the oxidation propensity of the dyes increased on insertion of thiophene unit in the conjugation pathway. These structural modifications fine-tuned the optical and electrochemical properties of the dyes. Additionally, the presence of tert-butyl groups on the carbazole nucleus minimized the intermolecular interactions which benefited the performance of DSSCs. The dyes served as efficient sensitizers in DSSCs owing to their promising optical and electrochemical properties. The efficiency of DSSCs utilizing these dyes as sensitizers ranged from 4.22 to 6.04%. The tert-butyl groups were found to suppress the recombination of injected electrons which contributed to the increment in the photocurrent generation (JSC) and open circuit voltage (VOC). A dye with carbazole donor functionalized with tert-butyl groups and the conjugation bridge composed of 2,7-disubstituted carbazole and thiophene fragments exhibited higher VOC value. However, the best device efficiency was observed for a dye with unsubstituted carbazole donor and the π-linker featuring carbazole and bithiophene units due to the high photocurrent generation arising from the facile injection of photogenerated electrons into the conduction band of titanium dioxide (TiO2) facilitated by the low-lying LUMO.

Co-sensitization is a well-known method to broaden the light absorption wavelength. The co-sensitizer adsorption kinetics in dye-sensitized solar cells (DSSCs) is investigated by using simple UV–visible absorption spectra and images for co-sensitizers before and after TiO2 films soaking. The adsorption rate and surface coverage on TiO2 films of the co-sensitizers, i.e., a metal-free squaraine dye (SQ2) and a diarylaminofluorene-based organic dye (JD1), are also studied to explain the performance of DSSCs. The power conversion efficiency (η) of the co-sensitized DSSC is enhanced due to the cooperative interactions of the organic co-sensitizers. A wide absorption wavelength (400–750 nm) for light harvesting is found for the co-sensitizer at the molar ratio of 6 to 4 for JD1 to SQ2 dye, and thereby an η value of 6.36% is achieved for the pertinent DSSC, which is much higher than those of the cells sensitized with individual dyes absorbing narrow wavelength of light, i.e., η of 5.44% and 4.11% for the DSSC sensitized with JD1 (absorption wavelength from 400 to 550 nm) and SQ2 dye (absorption wavelength from 550 to 750 nm), respectively.

An improved light-harvesting ruthenium dye with an alkyl bithiophene group, designated as CYC-B1, is employed as the photosensitizer for a zinc oxide (ZnO)-based dye-sensitized solar cell (DSSC). ZnO films with N3 and CYC-B1 dyes exhibit different surface appearances. Interestingly, the ZnO nanocrystal electrode surface with CYC-B1 dye is found to be almost free from Zn 2+ /dye-agglomerations, usually observed in the case of other commercial ruthenium dyes for such an electrode surface, e.g., N3 dye. Owing to this favorable effect of the CYC-B1 dye, the DSSC with a ZnO film (designated as ZN20) sensitized with this dye exhibited an average efficiency ( η ) of 4.85 ± 0.03%, which is about 94% higher than the η of the cell with N3 dye (2.50 ± 0.12%). The enhancements of the cell with CYC-B1 dye are explained by analyzing the electrochemical impedance spectra (EIS) and laser-induced photocurrent transients. Further, polymethylmethacrylate (PMMA) spheres with uniform sizes of ca. 300 nm are synthesized and incorporated to template the ZN20 film (designated as PMMA-ZN20); this PMMA-ZN20 film is used as the scattering layer and it is coated on the underlayer ZN20 film to make the photoanode film (ZN20/PMMA-ZN20) of a DSSC. The thus fabricated DSSC shows an η of 5.40 ± 0.03%.

A coral-like film of nickel@nickel sulfide (Ni@NiS) was obtained on a conducting glass through an electrochemical method, in which the Ni functioned as a template. Three types of Ni thin films were electrodeposited on fluorine-doped tin oxide (FTO) substrates by a pulse current technique at the passed charge densities of 100, 200, and 300 mC cm−2, which rendered custard apple-like, coral-like, and cracked nanostructures, respectively. Subsequently, nickel sulfide films were coated on these Ni films by using a pulse potential technique. Due to the template effect of the Ni films, the composite films of Ni@NiS also assumed the same structures as those of their nickel templates. In each case of the films the particle of the film assumed a core–shell structure. The Ni@NiS coated FTO glasses were used as the counter electrodes for dye-sensitized solar cells (DSSCs). The DSSC with the coral-like Ni@NiS film on its counter electrode exhibits the highest power conversion efficiency (η) of 7.84%, while the DSSC with platinum film on its counter electrode shows an η of 8.11%. The coral-like Ni@NiS film exhibits multiple functions, i.e., large surface area, high conductivity, and great electrocatalytic ability for iodine/triiodine (I−/I3−) reduction. X-ray photoelectron spectroscopy (XPS), X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), and four-point probe technique were used to characterize the films. The photovoltaic parameters are substantiated using incident photon-to-current conversion efficiency (IPCE) curves, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization plots. The IPCE curves were further used to calculate theoretical short-current densities of the cells.

High-surface-area (118 m2 g−1) microflower-like TiO2 (MF-TiO2), consisting of TiO2 nanopetals, is synthesized for the photoanode of a quasi-solid-state dye-sensitized solar cell (QSSDSSC). The QSSDSSC with the MF-TiO2 film scattering layer (SL) shows an efficiency (η) of 5.30 %, whereas its counterpart with a commercial SL shows an η of 3.90 %.

A new type of ionic liquid that contains a nitroxide radical (NOC) and iodide as two redox couples, JC-IL, has been suc- cessfully synthesized for high-performance dye-sensitized solar cells (DSSCs). Both of the redox couples exhibit distinct redox potentials and attractive electrochemical characteristics. The UV/Vis absorption spectra of JC-IL shows a low-intensity peak compared to the strong absorption of I2 in the wavelength region of 350-500 nm. The high open-circuit voltage of DSSCs with JC-IL is over 850 mV, which is approximately 150 mV higher than that of the DSSCs with a standard iodide electro- lyte. The dramatic increase in the standard heterogeneous electron-transfer rate constant leads to an increase in the short-circuit current for JC-IL compared to that of 2,2,6,6-tetra- methylpiperidin-N-oxyl (TEMPO). DSSCs with the JC-IL electro- lyte show promising cell efficiencies if coupled with dyes CR147 (8.12 %) or D149 (6.76 %). The efficiencies of the DSSCs based on the JC-IL electrolyte are higher than those of DSSCs based on either TEMPO electrolyte or standard iodide electro- lyte alone.

New metal free dianchoring organic dyes featuring A–π–D–π–D–π–A (acceptor – π bridge – donor – π bridge – donor – π bridge – acceptor) configuration have been designed incorporating fluorene and oligothiophene units and successfully synthesized. Elongating the conjugation pathway between the donor and acceptor units altered the distance between the anchoring sites besides the absorption and redox properties. These dyes exhibited broad and intense absorption when compared to the corresponding monoanchoring donor–π–acceptor congeners. Though the dye containing bithiophene unit exhibited comparatively low Voc due to low electron life time and facile back electron transfer, showed high power conversion efficiency arising from the good light-harvesting capability attributable to the intense absorption peak in the visible region and enhanced interfacial electron transfer rate. This work demonstrates that the smaller distance of separation between the anchoring units increases the insulating capacity of the molecular layer which retards the back electron transfer.

Seven ionic liquids (ILs) based on asymmetric trialkyl sulfonium and tetraalkylammonium cations with bis(trifluoromethanesulfonyl)imide anion were prepared and characterized. Physico-chemical and electrochemical properties of these ionic liquids including density, decomposition temperature, viscosity and conductivity were determined. The photovoltaic parameters of dye-sensitized solar cells (DSSCs) containing these sulfonium and ammonium ion-based ILs were compared. Among these two groups of ILs, the DSSCs with sulfonium cation-based ILs show higher cell efficiencies than that of ammonium counterpart due to lower charge transfer resistance exhibited by the former when compared to the latter, as confirmed by electrochemical impedance spectroscopy (EIS). The best cell efficiency achieved in this work was 4.61%. Moreover, long-term durability of the quasi-solid-state DSSCs at 50 °C was investigated.

The pure organic dyes are investigated recently because of its high extinction coefficient and relatively low cost. In order to enhance the performance of the organic dyes, co-sensitization strategy is applied. The co-sensitization by the absorption of SQ2/5c shows enhanced photovoltaic performance for the pertinent DSSCs, which leads to a broader light harvesting window (400–750 nm) and a higher overall efficiency of 6.24% while the performances of DSSCs with the individual dyes are 5.33% (5c) and 3.98% (SQ2), respectively. Furthermore, the overall efficiency can be further improved to 6.71% with the incorporation of chenodeoxycholic acid (CDCA). In addition, the incident photon-to-current conversion efficiency (IPCE) and UV–visible absorption spectra are also used to explain and support the behavior of the co-sensitized solar cells. The investigation of the long-term stability of the DSSC based on co-sensitization of SQ2/5c dyes with the use of binary ionic liquid is performed. The DSSC with the co-sensitization strategy possesses an unfailing durability up to 1000 h.

The chemical stability of ZnO against acidic dye molecules is an important issue to be improved in a dye-sensitized solar cell (DSSC). In this study, ZnO nanowires (ZnO-NWs) are prepared on a FTO glass through chemical bath deposition, and then the surface of ZnO-NWs are precisely coated with a thin TiO 2 layer step by step using a simple dipping–rinse–hydrolyzation (DRH) process to create the core–shell structure of ZnO@TiO 2 nanowires (ZnO@TiO 2 -NWs) for improving the chemical stability of ZnO. This core–shell structure of ZnO@TiO 2 -NWs on a FTO glass is further used as the photoanode of a DSSC with an acidic N3 dye as sensitizer. The TiO 2 shell acts not only as a protective layer to avoid the formation of Zn 2+ /dye complexes on the surface of ZnO-NWs, but also as a barrier against the recombination of injected electrons with the triiodide ions at the interface of ZnO-NWs and the electrolyte. A higher efficiency of 1.17% is achieved for the core–shell ZnO@TiO 2 -NWs based DSSC with optimized dye sensitization time and DRH cycles, when compared to the optimized cell with pristine ZnO-NWs (0.75%).

Titanium-based ceramic nanoparticles, i.e. , titanium nitride nanoparticles (TiN-NPs) and titanium carbide nanoparticles (TiC-NPs), are used on counter electrodes (CEs) for quantum-dot-sensitized solar cells (QDSSCs). The QDSSC with TiC-NPs-CE exhibits the highest solar-to-electricity conversion efficiency ( η ) of 2.11 ± 0.06%, which is higher than that of the cell with sputtered-Au-CE (1.64 ± 0.06%). This is due to the higher electrocatalytic ability of the TiC-NPs for reducing the polysulfide (S x 2− ) ions and the lower charge-transfer resistance at the interface of the CE and the electrolyte. Meanwhile, the three-dimensional structure of the Ti-based ceramic materials also acts as an extended charge-transfer surface, which facilitates electron transfer on the CE toward S x 2− ions. Explanations are substantiated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and incident photon-to-current conversion efficiency (IPCE) curves.

New organic dyes containing diphenylamine donor, 2,7-carbazolyl π-linker, and cyanoacrylic acid acceptor have been synthesized and characterized. They possess red-shifted absorption with high molar extinction coefficient when compared to the corresponding dyes with fluorene or phenyl units in the conjugation. The dye-sensitized solar cells fabricated using these dyes as sensitizers exhibited power conversion efficiencies as high as 6.8% which increased to 7.2% when chenodexoycholic acid (CDCA) was used to impede dye aggregation. The DSSCs with ionic liquid electrolytes displayed marked stability over 1000 h.

A ZnO composite film with an electron-collection center of ZnO nanorods (ZnNRs) embedded in a ZnO nanoparticle (ZnNP) film was fabricated on flexible photoanodes of back-illuminated dye-sensitized solar cells (DSSCs). Different lengths of the ZnNRs in ZnNP films were compared by considering their electron-collection and -scattering abilities. The morphologies and structures of the ZnO films were observed by examining their X-ray diffraction (XRD) patterns and scanning electron micrographs. The highest light-to-electricity conversion efficiency (η) of 2.17% was obtained for DSSCs, the ZnO composite film of which had about the same thickness of ZnNPs as the length of ZnNRs on its photoanode. At a thickness of only 7 μm of ZnNPs, the highest η was achieved with the composite film, leading to a 66.9% enhancement in efficiency compared to that obtained with only ZnNPs (1.30%). When the ZnNR length was shorter than the thickness of the ZnNP film, electrons in the ZnNPs film were not effectively transferred. On the other hand, if the ZnNRs were too long and stuck out of the ZnNP film, the incident light was scattered, resulting in less light utilization. These explanations were substantiated by electrochemical impedance spectra, laser-induced photo-voltage transients, and incident photon-to-electron conversion efficiency curves.

A quantum dot-sensitized solar cell (QDSSC) is fabricated using a composite layer, consisting of ZnO nanowires and ZnO nanoparticles (CL-ZnO) as its semiconductor film. The diameter and the thickness of each ZnO nanowire (ZNW) are ∼100 nm and ∼6 μm, respectively. The structure and morphology of the films with ZnO nanoparticles (ZNPs), ZNWs, and CL-ZnO are characterized by X-ray diffraction (XRD) patterns and scanning electron microscopic (SEM) images. Cadmium sulfide quantum dots (CdS QDs) are deposited on the ZNWs, ZNPs, and CL-ZnO by a successive ionic layer adsorption and reaction (SILAR) cycle. The highest efficiency (η) for the QDSSC sensitized by CdS (CdS-QDSSC) is obtained in the case of CL-ZnO photoanode, and this is attributed to significant improvement in the short-circuit photocurrent density (JSC) of the pertinent cell, which is 2.81- fold higher than that of the cell with ZNWs. Moreover, cadmium selenide quantum dots (CdSe QDs) are used as co-sensitizer along with the CdS QDs for the CL-ZnO semiconductor layer (film designated as CL-ZnO/CdS/CdSe), and the pertinent QDSSC showed much higher efficiency than the one obtained in the case of the cell using only CdS QDs as the sensitizer. Finally, a passivation layer of ZnS was deposited on the film of CL-ZnO/CdS/CdSe, and the cell with this film (CL-ZnO/CdS/CdSe/ZnS) showed an efficiency of 0.55%, the highest in this research. Electrochemical impedance spectra (EIS), UV–vis absorbance spectra, transmission electron microscopy (TEM), and incident photon-to-current conversion efficiency (IPCE) curves are used to substantiate the explanations.

A novel 2,7-diaminofluorene-based organic dye (coded as JD2) with the diarylaminofluorene unit as the electron donor and the cyanoacrylic acid as the acceptor as well as anchoring group in a donor-π–donor-π–acceptor architecture is used in a dye-sensitized solar cell (DSSC). The TiO 2 film thickness and the dye soaking time are optimized, and a coadsorbate of bis-(3,3-dimethyl-butyl)-phosphinic acid (DINHOP) is added to the dye solution to reform the cell performance. Effects of the additives, N -methylbenzimidazole (NMBI), guanidinium thiocyanate (GuSCN) or 4-tert-butylpyridine (TBP) in the electrolyte on the photovoltaic performance of the DSSC are studied. Effects of change of DINHOP concentration in JD2 dye solution, change of ratio of LiI to 1,2-dimethyl-3-propylimidazolium iodide (DMPII), and change of concentration of I 2 in the electrolyte on the photovoltaic performance of the DSSC are studied. A light-to-electricity conversion efficiency ( η ) of 6.31% is achieved for the JD2 dye-based DSSC, which is one of the best efficiencies for a cell with an organic dye. Explanations are made with electrochemical impedance spectra (EIS), laser-induced photo–voltage transients, and incident photo-to-current conversion efficiency (IPCE) curves.

Carbon black (CB), multi-walled carbon nanotube (MWCNT), and graphene (GN) were examined as catalytic films on the counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). GN exhibits the best performance among these materials for the corresponding cell. A composite film of GN/Nafion® was next used as the catalytic film on the CE of a DSSC. Nafion® is demonstrated to be an excellent dispersant for inhibiting the aggregation of GN. A solar-to-electricity conversion efficiency (η) of 8.19% was achieved for the DSSC sensitized by TBA(Ru[(4-carboxylic acid-4′-carboxylate-2,2′-bipyridine)(4,4′-bis(5-(hexylthio)-2,2′-bithien-5′-yl)-2,2′-bipyridine)(NCS)2]), i.e., CYC-B11 dye, which was synthesized by our group, after the optimization of the composition of GN/Nafion®, and an η of 8.89% was exhibited for the cell with a sputtered-Pt (s-Pt) film on its CE under the same conditions. The significance of the cell with the composite film of GN/Nafion® lies in the fact that the expensive Pt is avoided in this case, thereby the cost of the pertinent DSSC was greatly reduced, even though its η (8.19%) is slightly smaller than that of the cell with the s-Pt film (8.89%).

A composite thin film of only 6 μm, consisting of a first layer of ZnO nanorods (ZNRs) and a second layer of ZnO nanoparticles (ZNPs), was deposited on a flexible Ti foil. The structures and morphologies of the films of ZNRs, ZNPs, and their composite (hereafter ZNRs/ZNPs) were studied by X-ray diffraction (XRD) patterns, scanning electron microscopic (SEM) and transmission electron microscopy (TEM) images. The Ti foil with the composite film was used as the photoanode of a flexible dye-sensitized solar cell (DSSC); an indium doped tin oxide/polyethylene naphthalate (ITO/PEN) substrate with a thin layer of platinum was used as the counter electrode. A power conversion efficiency (η) of 2.19% was achieved for the DSSC with ZNRs/ZNPs, through back-illumination, which is higher than that of the cell with only ZNPs (1.80%); the DSSC with bare ZNRs showed a very poor efficiency of 0.90%. Explanations are substantiated by electrochemical impedance spectra (EIS), laser-induced photo-voltage transients, and incident photon-to-electron conversion efficiency (IPCE) curves.

This communication demonstrated the technique of using microemulsion to synthesize ZnO crystals with a variety of morphologies. A nearly 30% improved efficiency of a dye-sensitized solar cell can be obtained by using one of the synthesized crystals with coral-like structure, as compared to the commercially available ZnO particles.

a b s t r a c t Conducting polymer materials, i.e., polythiophene (PT), polypyrrole (PPy), and poly(3,4- ethylenedioxythiophene) (PEDOT) were used to prepare counter electrodes (CEs) for quantum-dot-sensitized solar cells (QDSSCs). The QDSSC with PEDOT-CE exhibited the highest solar-to-electricity conversion efficiency (� ) of 1.35%, which is remarkably higher than those of the cells with PT-CE (0.09%) and PPy-CE (0.41%) and very slightly higher than that of the cell with sputtered- gold-CE (1.33%). Electrochemical impedance spectra (EIS) show that this highest conversion efficiency of the PEDOT-based cell is due to higher electrocatalytic activity and reduced charge transfer resistance at the interface of the CE and the electrolyte, compared to those in the case of the cells with other conducting polymers and bare Au. Furthermore, the influences of morphology of the PEDOT film and the charge passed for its electropolymerization on the performance of its QDSSC were also studied. The higher porosity and surface roughness of the PEDOT matrix, with reference to those of other polymers are understood to be the reason for PEDOT to possess higher electrocatalytic activity at its interface with electrolyte.

A flexible photoanode was prepared for a dye-sensitized solar cell (DSSC), using a titanium (Ti) foil as the substrate, titanium oxide nanotubes (TNTs) as the underlayer, and TiO 2 nanoparticles (TNPs) as the overlayer; the TNTs were intended to provide one-dimensional (1-D) electron transfer paths at the interface of the Ti foil and the TNPs. The Ti foil was subjected to anodization at a constant applied potential to obtain the TNTs. Scanning electron microscopic (SEM) images show a steady increase in the diameters of the TNTs with the increase of the anodization potential from 20 to 50 V. X-ray diffraction (XRD) patterns indicate anatase (1 0 1) crystal plane for all the TNTs. The DSSCs with the TNTs as the underlayer show higher short-circuit current density ( j SC ) and higher light-to-electricity conversion efficiency ( η ), compared to those of a DSSC without TNTs. An efficiency of 6.68% was achieved for the DSSC with TNTs as the underlayer, which is 20.4% higher than that obtained for a cell with only a film of TNPs. This efficiency is also one of the best for a back-illuminated DSSC with Ti foil as the substrate. Charge transfer resistances of the cells were investigated by electrochemical impedance spectroscopy (EIS). Laser-induced photo-potential transient and photo-current transient techniques were respectively used to calculate the electron lifetime and electron diffusion coefficient in Ti/TNTs/TNPs films.

Monodispersed polystyrene (PS, ca. 300 nm) latex particles are incorporated into a TiO2 film. A polystyrene-modified TiO2 film (M-TiO2) with micro-cluster structure, containing micro/nano-composite pores is thus obtained after sintering. Cadmium sulfide (CdS) quantum dots (CdS-QDs) are accumulated over M-TiO2 and bare TiO2 films (B-TiO2) by successive ionic layer adsorption and reaction (SILAR); we designate these films as M-TiO2/CdS and B-TiO2/CdS, respectively. Influence of SILAR cycles used for depositing CdS on B-TiO2 and M-TiO2 films on the performance of the pertinent quantum dot-sensitized solar cells (QDSSCs) is studied. The QDSSC with 6 SILAR cycles of M-TiO2/CdS (M-TiO2/CdS6) exhibited a solar-to-electricity conversion efficiency (η) of 1.79%, while the cell with B-TiO2/CdS5 shows an η of 1.35%, under the illumination of one sun. Moreover, guanidine thiocyanate (GuSCN) is found to be a promising additive to the polysulfide electrolyte. The additive renders higher conversion efficiency (2.01%) to its QDSSC. Durability of the CdS-QDSSC is also tested. Scanning electron microscopy (SEM) is used to obtain the images of TiO2 films and energy-dispersive X-ray spectroscopy (EDX) is employed to study the stoichiometric ratios of M-TiO2/CdS and B-TiO2/CdS. Incident photon-to-current conversion efficiencies (IPCE) of the QDSSCs are obtained to confirm the JSC behaviors of the cells.

A composite poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]-dioxepine) and platinum (PProDOT-Et 2 /Pt) film was prepared for using as a counter electrode (CE) catalyst in a dye-sensitized solar cell (DSSC). Four composite films were prepared by electropolymerization of ProDOT-Et 2 on indium tin oxide (ITO) conducting glass, followed by Pt sputtering for 10, 30, 120, and 720 s. The Pt content in the composite film was verified by energy dispersive X-ray spectroscopy (EDX). The composite films possessed three-dimensional (3D) porous structures, as determined by scanning electron microscopy (SEM). The DSSC with the composite film that was subject to 10 s of Pt deposition (PProDOT-Et 2 /Pt-10 s) exhibited the highest solar to electricity conversion efficiency ( η ) of 6.68%, while the cells with the bare polymer film (PProDOT-Et 2 ) and Pt that was sputtered for 720 s (s-Pt-720 s) demonstrated efficiencies of 4.76% and 6.43%, respectively. The cell photovoltaic parameters were substantiated through dark current, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) analyses. Incident photon-to-current conversion efficiency (IPCE) curves were used to explain the cell photocurrent behaviors.

A novel class of organic dyes containing pyrenoimidazole donors, cyanoacrylic acid acceptors, and oligothiophene π-linkers has been synthesized and characterized. The electro-optical properties of these dyes can be tuned by changing the conjugation length of the π-linkers. A dye containing terthiophene in the conjugation pathway exhibited a solar energy-to-electricity conversion efficiency of 5.65%.

An energy-economical dye-sensitized solar cell (DSSC) with highly flexible Ti/TiO2 photoanode was developed through a low-temperature process, using a binder-free TiO2 paste. Ti foils, coated with the binder-free TiO2 films were annealed at various temperature. Scanning electron microscopic (SEM) images of the films show uniform, mesoporous and crack-free surface morphologies as well as interpenetrated TiO2 network. DSSCs with binder-free TiO2 films annealed at 450, 350, 250 and 120°C show solar-to-electricity conversion efficiencies (η) of 4.33, 4.34, 3.72 and 3.40%, respectively, which are comparable to the efficiency of 4.56% obtained by using a paste with binder and annealing it at 450°C; this observation demonstrates the benefits of a binder-free TiO2 paste for the fabrication of energy-fugal DSSCs. On the other hand, when organic binder was used in the TiO2 paste for film preparation, a drastic deterioration in the cell performance with decreasing annealing temperature is noticed. Laser-induced photo-voltage transient technique is used to estimate the electron lifetime in various Ti/TiO2 films. Electrochemical impedance spectroscopic (EIS) analysis shows that the lower the annealing temperature of the TiO2 coated Ti foil, the larger the charge transfer resistance at the TiO2/dye/electrolyte interface (Rct2). Copyright © 2011 John Wiley & Sons, Ltd.

Titanium nitride (TiN) or its thermally treated version is incorporated into the gel electrolyte of a dye-sensitized solar cell (DSSC) and the consequent effects are investigated in terms of photovoltaic performance of the cell. The gel electrolyte is essentially prepared by using poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP). With an addition of 3 wt% TiN, the solar-to-electricity conversion efficiency ( η ) of the DSSC reaches 5.33% from 4.15% of the cell without TiN. X-ray diffraction (XRD) spectra of thermally treated-TiN (tt-TiN) clearly shows the partial conversion of TiN into TiO 2 with both anatase and rutile crystal phases. The DSSC with the incorporation of 3 wt% of tt-TiN into its electrolyte shows a further improved efficiency of 5.68%, with reference to the efficiency of TiN-incorporated DSSC. The cell with 3 wt% of tt-TiN also shows unfailing at-rest stability after more than 1000 h. Electrochemical impedance spectroscopy (EIS) is used to obtain charge transfer properties of the cells. Crystallinity and crystalline phases are analyzed by X-ray diffraction (XRD) spectra. Surface morphologies are observed with scanning electron microscopy (SEM). IPCE curves substantiate the variations in short circuit photocurrents.

Various weight percentages of titanium nitride (TiN) and thermally-treated titanium nitride (tt-TiN) are incorporated into the binder-free TiO 2 films, prepared at low temperature (LT, 120 °C), and the corresponding dye-sensitized solar cells (DSSCs) are made. Effects of their incorporation on the photovoltaics of the DSSCs are studied. With the incorporation of 0.125 wt% of TiN in a TiO 2 film of only 5.5 μm-thickness, the corresponding solar-to-electricity conversion efficiency ( η ) has reached to 3.40% from 2.38% of a cell with a bare TiO 2 film of same thickness; this increase in efficiency is attributed to the higher electron conductivity and longer electron life time in the TiO 2 film with TiN. Incorporation of 1.0 wt% of tt-TiN into the TiO 2 film has further improved the conversion efficiency to 3.77%; this further enhancement in the efficiency is attributed to the partial conversion of TiN into TiO 2 due to the thermal treatment (450 °C). X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to study the partial conversion of TiN into TiO 2 . Other explanations are supported by the data of UV-absorption spectra, electrochemical impedance spectroscopy (EIS), and laser-induced photo-voltage transients.

Highly efficient and stable back illumination dye-sensitized solar cell (BIL-DSSC) is developed using its Pt-counter electrode (Pt-CE) as the light-irradiating surface. Photovoltaic parameters are measured for DSSCs with Pt-CEs obtained with different sputtering periods of platinum layer. By optimizing the transmittance and catalytic property of the platinum layer on the counter electrode, a light-to-electricity conversion efficiency (η) of 7.54% is achieved with back illumination at 100 mW cm−2, when the platinum deposition time is 30 s. The effects of platinum layers with different sputtering periods on the photovoltaic characteristics of the respective DSSCs are explained in terms of transmittance and catalytic activity of the layers. A comparative study is also made on the durability of the DSSCs with BIL and front illumination (FIL), in which the respective DSSCs are previously subjected to UV-soaking for different periods of time under simulated conditions of back and front illuminations; at-rest stability tests for such UV-soaked DSSCs carried out through BIL and FIL suggest a far higher stability in favor of the BIL-DSSC, compared to that of the FIL-DSSC. Explanations are substantiated with transmittance spectra, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and absorption spectra.

Back-illuminated dye-sensitized solar cell (DSSC) based on a flexible TiO2/Ti foil photoanode and a high transparent platinum counter electrode (Pt-CE) has been developed by using a net-like Pt-CE ...

Two unsymmetrical squaraines, where the electron-rich 3,4-ethylenedioxythiophene or bithiophene conjugated fragment was used to link unconventionally the squaraine core and the hexyloxyphenyl amino group, were applied for DSCs. The corresponding photovoltaic devices exhibit an attractively panchromatic response and also convert a portion of the near-infrared photons into electricity.

The effects of four factors, i.e., (i) sputter-deposition time of platinum (Pt) film, (ii) sintering temperature of TiO2-coated Ti foil (Ti/TiO2), (iii) thickness of Ti foil, and (iv) concentration of iodine are reported for the photovoltaic performance of a back-illuminated flexible dye-sensitized solar cell (DSSC) with Ti foil substrate for the TiO2 layer. Optimization of these four factors yields a solar-to-electricity conversion efficiency (� ) of 5.95%. Transmittance spectra, cyclic voltammetry (CV), electrochemical impedance spectra (EIS), X-ray diffraction (XRD), scanning electron micrographs (SEM), and laser-induced photovoltage transient technique are used to substantiate the explanations. © 2010 Elsevier B.V. All rights reserved.

A quasi solid-state dye-sensitized solar cell (DSSC) is fabricated using 1-propyl-3-methylimidazolium iodide (PMII) and polyaniline-loaded carbon black (PACB) as the composite electrolyte. The electrolyte without added iodine is sandwiched between TiO 2 working electrode and platinum counter electrode (CE). A power conversion efficiency ( η ) of 5.81% is achieved with this type of cell. With the addition of 1-ethyl-3-methylimidazolium thiocyanate (EMISCN), a low-viscosity ionic liquid (IL), the cell with the binary ionic liquid (bi-IL) renders an efficiency of 6.15%, the best for any quasi solid-state DSSC without the addition of iodine. To fabricate a low cost DSSC using the bi-IL, the platinum layer of the counter electrode is replaced with a polymer layer, 3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4] dioxepine (PProdot-Et 2 ) through electrodeposition, and the corresponding DSSC shows an efficiency of 5.27%. At-rest stability of the quasi solid-state DSSC with bi-IL is compared with that of a liquid electrolyte DSSC at room temperature; the power conversion efficiency of the former shows a decrease of hardly 3% after 1000 h, while that of the latter shows a decrease of about 30%. The quasi solid-state cell shows unfailing durability at 70 °C.

We have fabricated organic photovoltaic devices with blends of poly[9,9′-dioctyl-fluorene- co -bithiophene] (F8T2) and fullerene as an electron donor and electron acceptor, respectively. A significant improvement of the photovoltaic efficiency was found in device by using active materials with complementary spectra. The different weight ratios of composite film were also performed to correlate between morphology and the device performance. A power conversion efficiency (PCE) up to 2.0% with an open-circuit voltage of 0.85 V and a short-circuit current ( J SC ) of 5.3 mA/cm 2 , was achieved by blending the F8T2 with [6,6]-phenyl-C71-butyric acid methyl ester (PC[70]BM).