Fullerol–Titania Charge‐Transfer‐Mediated Photocatalysis Working under Visible Light

The development of visible‐light‐active photocatalysts is being investigated through various approaches. In this study, C₆₀‐based sensitized photocatalysis that works through the charge transfer (CT) mechanism is proposed and tested as a new approach. By employing the water‐soluble fullerol (C₆₀(OH)_x) instead of C₆₀, we demonstrate that the adsorbed fullerol activates TiO₂ under visible‐light irradiation through the “surface–complex CT” mechanism, which is largely absent in the C₆₀/TiO₂ system. Although fullerene and its derivatives have often been utilized in TiO₂‐based photochemical conversion systems as an electron transfer relay, their successful photocatalytic application as a visible‐light sensitizer of TiO₂ is not well established. Fullerol/TiO₂ exhibits marked visible photocatalytic activity not only for the redox conversion of 4‐chlorophenol, I^?, and Cr^VI, but also for H₂ production. The photoelectrode of fullerol/TiO₂ also generates an enhanced anodic photocurrent under visible light as compared with the electrodes of bare TiO₂ and C₆₀/TiO₂, which confirms that the visible‐light‐induced electron transfer from fullerol to TiO₂ is particularly enhanced. The surface complexation of fullerol/TiO₂ induced a visible absorption band around 400–500 nm, which was extinguished when the adsorption of fullerol was inhibited by fluorination of the surface of TiO₂. The transient absorption spectroscopic measurement gave an absorption spectrum ascribed to fullerol radical cations (fullerol^.+) the generation of which should be accompanied by the proposed CT. The theoretical calculation regarding the absorption spectra for the (TiO₂ cluster+fullerol) model also confirmed the proposed CT, which involves excitation from HOMO (fullerol) to LUMO (TiO₂ cluster) as the origin of the visible‐light absorption.     

Unconventional Route to Oxygen‐Vacancy‐Enabled Highly Efficient Electron Extraction and Transport in Perovskite Solar Cells

The ability to effectively transfer photoexcited electrons and holes is an important endeavor toward achieving high‐efficiency solar energy conversion. Now, a simple yet robust acid‐treatment strategy is used to judiciously create an amorphous TiO₂ buffer layer intimately situated on the anatase TiO₂ surface as an electron‐transport layer (ETL) for efficient electron transport. The facile acid treatment is capable of weakening the bonding of zigzag octahedral chains in anatase TiO₂, thereby shortening staggered octahedron chains to form an amorphous buffer layer on the anatase TiO₂ surface. Such amorphous TiO₂‐coated ETL possesses an increased electron density owing to the presence of oxygen vacancies, leading to efficient electron transfer from perovskite to TiO₂. Compared to pristine TiO₂‐based devices, the perovskite solar cells (PSCs) with acid‐treated TiO₂ ETL exhibit an enhanced short‐circuit current and power conversion efficiency.     

An Organic Dyad Composed of Diathiafulvalene‐Functionalized Diketopyrrolopyrrole–Fullerene for Single‐Component High‐Efficiency Organic Solar Cells

A new low‐band gap dyad DPP‐Ful, which consists of covalently linked dithiafulvalene‐functionalized diketopyrrolopyrrole as donor and fullerene (C₆₀) as the acceptor, has been designed and synthesized. Organic solar cells were successfully constructed using the DPP‐Ful dyad as an active layer. This system has a record power‐conversion efficiency (PCE) of 2.2 %, which is the highest value when compared to reported single‐component organic solar cells.     

Low‐cost Nickel Complex Dye‐sensitized Titania Nanoparticle/nanotube Composites for Solar Cells

In this work, high‐performance dye‐sensitized solar cells (DSSCs) based on new low‐cost visible nickel complex dye (VisDye), TiO₂ nanoparticle/nanotube composites electrodes, carbon nanoparticles counter electrodes, and ionic liquids electrolytes have been fabricated. The electronic structure, optical spectroscopy, and electrochemical properties of the VisDye were studied. Experimental results indicate that it is beneficial to improve the electron transport and power conversion efficiency using the nickel complex VisDye and TiO₂ nanoparticle/nanotube composites. Under optimized conditions, the solar energy conversion efficiencies were measured. The short‐circuit current density (J_SC), the open‐circuit voltage (V_OC), the fill factor (FF), and the overall efficiency (η) of the DSSCs are 10.01 mA/cm², 516 mV, 0.68, and 3.52%, respectively. This study demonstrates that the combination of new VisDye with TiO₂ nanoparticle/nanotube composites electrodes and carbon nanoparticles counter electrodes provide a way to fabricate highly efficient dye‐sensitized solar cells in low‐cost production.     

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.     

Molecular Design Rule of Phthalocyanine Dyes for Highly Efficient Near‐IR Performance in Dye‐Sensitized Solar Cells

A series of zinc–phthalocyanine sensitizers ( PcS16 – 18 ) with different adsorption sites have been designed and synthesized in order to investigate the dependence of adsorption‐site structures on the solar‐cell performances in zinc–phthalocyanine based dye‐sensitized solar cells. The change of adsorption site affected the electron injection efficiency from the photoexcited dye into the nanocrystalline TiO₂ semiconductor, as monitored by picosecond time‐resolved fluorescence spectroscopy. The zinc–phthalocyanine sensitizer PcS18 , possessing one carboxylic acid directly attached to the ZnPc ring and six 2,6‐diisopropylphenoxy units, showed a record power conversion efficiency value of 5.9 % when used as a light‐harvesting dye on a TiO₂ electrode under one simulated solar condition.     

CdSe Quantum Dots and N719‐Dye Decorated Hierarchical TiO2 Nanorods for the Construction of Efficient Co‐Sensitized Solar Cells

Three‐dimensional hierarchical TiO₂ nanorods (HTNs) decorated with the N719 dye and 3‐mercaptopropionic or oleic acid capped CdSe quantum dots (QDs) in photoanodes for the construction of TiO₂ nanorod‐based efficient co‐sensitized solar cells are reported. These HTN co‐sensitized solar cells showed a maximum power‐conversion efficiency of 3.93 %, and a higher open‐circuit voltage and fill factor for the photoanode with 3‐mercaptopropionic acid capped CdSe QDs due to the strong electronic interactions between CdSe QDs, N719 dye and HTNs, and the superior light‐harvesting features of the HTNs. An electrochemical impedance analysis indicated that the superior charge‐collection efficiency and electron diffusion length of the CdSe QD‐coated HTNs improved the photovoltaic performance of these HTN co‐sensitized solar cells.     

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.     

CuSbS2‐Sensitized Inorganic–Organic Heterojunction Solar Cells Fabricated Using a Metal–Thiourea Complex Solution

The device performance of sensitizer‐architecture solar cells based on a CuSbS₂ light sensitizer is presented. The device consists of F‐doped SnO₂ substrate/TiO₂ blocking layer/mesoporous TiO₂/CuSbS₂/hole‐transporting material/Au electrode. The CuSbS₂ was deposited by repeated cycles of spin coating of a Cu‐Sb‐thiourea complex solution and thermal decomposition, followed by annealing in Ar at 500 °C. Poly(2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene)‐alt‐4,7(2,1,3‐benzothiadiazole)) (PCPDTBT) was used as the hole‐transporting material. The best‐performing cell exhibited a 3.1 % device efficiency, with a short‐circuit current density of 21.5 mA cm^?2, an open‐circuit voltage of 304 mV, and a fill factor of 46.8 %.     

TiO2 Nanospheres: A Facile Size‐Tunable Synthesis and Effective Light‐Harvesting Layer for Dye‐Sensitized Solar Cells

A facile route to synthesize amorphous TiO₂ nanospheres by a controlled oxidation and hydrolysis process without any structure‐directing agents or templates is presented. The size of the amorphous TiO₂ nanospheres can be easily turned from 20 to 1500 nm by adjusting either the Ti species or ethanol content in the reaction solution. The phase structure of nanospheres can be controlled by hydrothermal treatment. The TiO₂ nanospheres show excellent size‐dependent light‐scattering effects and can be structured into a light‐harvesting layer for dye‐sensitized solar cells with a quite high power conversion efficiency of 9.25 %.     

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.     

Photoanode Based on Chain‐Shaped Anatase TiO2 Nanorods for High‐Efficiency Dye‐Sensitized Solar Cells

Anatase TiO₂ nanorods with large specific surface areas and high crystallinity have been synthesized by surfactant‐free hydrothermal treatment of water‐soluble peroxotitanium acid (PTA). X‐ray diffraction and TEM analysis showed that all TiO₂ nanorods derived from PTA in different hydrothermal processes were in the anatase phase, and high aspect ratio TiO₂ nanorods with chain‐shaped structures were formed at 150 °C for 24 h by oriented growth. The nanorods were fabricated as photoanodes for high‐efficiency dye‐sensitized solar cells (DSSCs). DSSCs fabricated from the chain‐shaped TiO₂ nanorods gave a highest short‐circuit current density of 14.8 mA cm^?2 and a maximum energy conversion efficiency of 7.28 %, as a result of the presence of far fewer surface defects and grain boundaries than are present in commercial P25 TiO₂ nanoparticles. Electrochemical impedance spectroscopy also confirmed that DSSCs based on the TiO₂ nanorods have enhanced electron transport properties and a long electron lifetime.     

Enhancing the Performance of Dye‐Sensitized Solar Cells with a Gold‐Nanoflowers Box

To improve the electron collection, electron lifetime, and light‐harvesting efficiency of dye‐sensitized solar cells simultaneously, Au nanoflowers were prepared and used to cover the entire TiO₂ film. Deposition of Au nanoflowers around the TiO₂ film formed a light‐scattering “box” that covered the entire TiO₂ film. Compared with a light‐scattering layer that only covers the top surface of TiO₂, the Au‐nanoflowers box exhibited better light‐harvesting efficiency due to omnidirectional light scattering, faster electron transport (attributed to the formation of electron channels between the metallic Au nanoflowers and the electron‐collection electrode), and slower charge recombination. As a consequence, the short‐circuit photocurrent and open‐circuit photovoltage were both enhanced significantly, which improved the power conversion efficiency from 8.12 to 10.91 % (34 %) when an Au‐nanoflowers box was wrapped around the photoanode.     

Chiral Aggregates of Triphenylamine‐Based Dyes for Depleting the Production of Hydrogen Peroxide in the Photochemical Water‐Splitting Process

Recent studies on water‐splitting photoelectrochemical cells (PECs) have demonstrated the intriguing possibility of controlling the spin state in this chemical reaction to form H₂ and O₂ by exploiting the chirality of organic π‐conjugated supramolecular polymers. Although this fascinating phenomenon has been disclosed, the chiral supramolecular materials reported thus far are not optimized for acting as efficient photosensitizer for dye‐sensitized PECs. In this work we report on the design, synthesis, and characterization of chiral supramolecular aggregates based on C₃‐symmetric triphenylamine‐based dyes that are able to both absorb visible light and control the spin state of the process. Variable temperature‐dependent spectroscopic measurements reveal the assembly process of the dyes and confirm the formation of chiral aggregates, both in solution as well as on solid supports. Photoelectrochemical measurements on TiO₂‐based anodes validate the advantage of using chiral supramolecular aggregates as photosensitizer displaying higher photocurrent compared to achiral analogues. Moreover, fluorimetric tests for the quantification of the hydrogen peroxide produced, confirm the possibility of controlling the spin of the reaction exerting spin‐selection with chiral supramolecular polymers. These results represent a further step towards the next‐generation of organic‐based water‐splitting solar cells.     

Nd‐Doped TiO2 Nanorods: Preparation and Application in Dye‐Sensitized Solar Cells

Monodispersed Nd‐doped TiO₂ nanorods (20 nm×2 nm) were synthesized by solvothermal methods and characterized by TEM, XRD, and EDS. Application of the nanorods for modifying conventional photoanodes in dye‐sensitized solar cells (DSSCs) was investigated. Data show that, after modification, an enhancement of the incident‐photon‐to‐current conversion efficiency (IPCE) in the whole range of visible light was observed and an increase of 33.3 % for overall conversion efficiency was achieved. Our mechanistic proposal is that Nd ions doped on TiO₂ nanorods to some extent enhance the injection of excited electrons and decrease the recombination rate of the injected electrons.     

Efficient Solution‐Processed Bulk Heterojunction Solar Cells by Antiparallel Supramolecular Arrangement of Dipolar Donor–Acceptor Dyes

A series of dipolar donor–acceptor (D –A) chromophores with aminothiophene donor and different heterocyclic acceptor units is reported. By modulation of the acceptor strength, absorption bands over the whole visible spectrum are accessible as well as adjustment of the frontier molecular orbital levels. The performance of the chromophores in blends with fullerene acceptors in solution‐processed bulk heterojunction solar cells was studied and related to the molecular properties of the dyes. In particular, the effect of the large ground‐state dipole moments of these dyes was investigated by single crystal X‐ray analysis, which revealed antiparallel dimers, resulting in an annihilation of the dipole moments. This specific feature of supramolecular organization explains the excellent performance of merocyanine dyes in organic solar cells. With blends of HB366 :PC₇₁BM, the most efficient solar cell with a V_OC of 1.0 V, a J_SC of 10.2 mA cm⁻², and a power‐conversion efficiency of 4.5 % was achieved under standard AM1.5, 100 mW cm⁻² conditions. Under reduced lighting conditions, even higher efficiencies up to 5.1 % was obtained.     

Structural Control of Hierarchically‐Ordered TiO2 Films by Water for Dye‐Sensitized Solar Cells

A facile way of controlling the structure of TiO₂ by changing the amount of water to improve the efficiency of dye‐sensitized solar cells (DSSCs) is reported. Hierarchically ordered TiO₂ films with high porosity and good interconnectivity are synthesized in a well‐defined morphological confinement arising from a one‐step self‐assembly of preformed TiO₂ (pre‐TiO₂) nanocrystals and a graft copolymer, namely poly(vinyl chloride)‐g‐poly(oxyethylene methacrylate). The polymer–solvent interactions in solution, which are tuned by the amount of water, are shown to be a decisive factor in determining TiO₂ morphology and device performance. Systematic control of wall and pore size is achieved and enables the bifunctionality of excellent light scattering properties and easy electron transport through the film. These properties are characterized by reflectance spectroscopy, incident photon‐to‐electron conversion efficiency, and electrochemical impedance spectroscopy analyses. The TiO₂ photoanode that is prepared with a higher water ratio, [pre‐TiO₂]:[H₂O]=1:0.3, shows a larger surface area, greater light scattering, and better electron transport, which result in a high efficiency (7.7 %) DSSC with a solid polymerized ionic liquid. This efficiency is much greater than that of commercially available TiO₂ paste (4.0 %).     

Sub‐Bandgap Excitation‐Induced Electron Injection from CdSe Quantum Dots to TiO2 in a Directly Coupled System

We show that the sub‐bandgap excitation of a directly coupled CdSe quantum dot (QD)–TiO₂ system induces electron injection from CdSe levels to the conduction band of TiO₂, leading to spectral extension of the light response. We anticipate that this study presents a useful guideline for improving the conversion efficiency of QD‐sensitized solar cells.     

Photocurrent Enhancement of Dye‐Sensitized Solar Cells owing to Increased Dye‐Adsorption onto Silicon‐Nanoparticle‐Coated Titanium‐Dioxide Films

The inverse‐micellar preparation of Si nanoparticles (Nps) was improved by utilizing sodium naphthalide. The Si Nps were subsequently functionalized with 4‐vinylbenzoic acid for their attachment onto TiO₂ films of dye‐sensitized solar cells (DSSCs). The average diameter of the COOH‐functionalized Si (Si? COOH) Nps was 4.6(±1.7) nm. Depth profiling by secondary‐ion mass spectrometry revealed that the Si Nps were uniformly attached onto the TiO₂ films. The number of Ru^II dye molecules adsorbed onto a TiO₂ film that was treated with the Si? COOH Nps was 42 % higher than that on the untreated TiO₂ film. As a result, DSSCs that incorporated the Si? COOH Nps exhibited higher short‐circuit photocurrent density and an overall energy‐conversion efficiency than the untreated DSSCs by 22 % and 27 %, respectively. This enhanced performance, mostly owing to the intramolecular charge‐transfer to TiO₂ from the dye molecules that were anchored to the Si? COOH Nps, was confirmed by comparing the performance with two different Ru^II–bipyridine dyes (N719 and N749).     

Sb2Se3‐Sensitized Inorganic–Organic Heterojunction Solar Cells Fabricated Using a Single‐Source Precursor

The photovoltaic performance of Sb₂Se₃‐sensitized heterojunction solar cells, which were fabricated by a simple deposition of Sb₂Se₃ on mesoporous TiO₂ by an approach that features multiple cycles of spin coating with a single‐source precursor solution and thermal decomposition, is reported. Poly[2,6‐(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene)‐alt‐4,7(2,1,3‐benzothioadiazole)] was used as the hole‐transporting material. The most efficient cell exhibited a short‐circuit current density of 22.3 mA cm^?2, an open‐circuit voltage of 304.5 mV, and a fill factor of 47.2 %, yielding a power conversion efficiency of 3.21 % under standard test conditions (irradiation of 1000 W m^?2, air mass=1.5 G). The results of this study imply that the developed approach has a high potential as a simple and effective route for the fabrication of efficient and inexpensive solar cells.