Band gap engineering of TiO2 nanostructure-based dye solar cells (DSCs) fabricated via electrophoresis

This work describes a simple method utilizing electrophoretic deposition (EPD) as versatile technique to deposit of commercial TiO₂ (P25) nanopartcles (NPs) films on the fluoride-doped tin oxide (FTO) substrate. The main goal of this study is investigating the effects of surface treatment on the properties of nanoporous P25 electrodes in order to efficiently control and optimize the main fabrication step of the dye-sensitized solar cells (DSSCs). In order to increase of the electron transfer efficiency in DSSC, post-treatment of P25 films using TiCl₄ has been carried out. As a result, cell efficiencies were improved about 40%. Solar cells based on a core–shell structure, including a ZnO as shell and a P25 as core, have been investigated. Results demonstrated that ZnO/P25 film electrode was enable to enhance of short-circuit photocurrent density (J_SC) and consequently solar conversion efficiency for a DSSC by 10%, compared to those of a DSSC containing a bare P25 film electrode. The results were attributed to increase the concentration of free electrons in the conduction band (CB) of P25.     

Dye sensitized solar cells (DSSCs) based on modified iron phthalocyanine nanostructured TiO2 electrode and PEDOT:PSS counter electrode

An iron phthalocyanine with tetra-sulphonated substituents (FeTsPc) was used as photosentizer for the development of dye sensitized nanostructured TiO₂ solar cells. The influence of surface modification (TiO₂ film treated with HCl and HNO₃) and thermal annealing of TiO₂ photo-electrode on the performance of dye sensitized solar cell (DSSC) having structure FTO/TiO₂–FeTsPc/electrolyte/PEDOT:PSS (carbon added)/FTO was investigated through the analysis of current–voltage characteristics under illumination and electrochemical impedance spectra (EIS). The improvement in crystallinity of TiO₂, decrease in the internal surface area and adsorbed amount of dye and increase in the lifetime of injected electrons upon thermal annealing of TiO₂ photo-electrode affects the photovoltaic properties of DSSC. The increase in power conversion efficiency of DSSC based on nitric acid treatment for the photo-electrode is mainly attributed to the increase in photocurrent. A comparative photovoltaic investigation of DSSCs using HCl-treated TiO₂ photo-electrode, indicates that the HNO₃-treated photo-electrode retards back electron transfer at the interface with electrolyte and increases the amount of dye.     

Mesoporous (N, S)-codoped TiO2 nanoparticles as effective photoanode for dye-sensitized solar cells

(N, S)-codoped titania (TiO₂) is synthesized by a simple template-free solvothermal method as photoanode for dye-sensitized solar cells (DSSCs). The results confirm that N and S have been doped into the lattice of anatase, which can enhance the visible-light absorbance and promote the electron transportation in TiO₂. The prepared (N, S)-codoped TiO₂ exhibits pure anatase phase mesoporous nanoparticles with average diameter of 60 nm. Mixing (N, S)-codoped TiO₂ with Degussa P25 as photoanode results in the improvement of open-circuit voltage and short-circuit photocurrent density of DSSC. And the corresponding DSSC obtains a high conversion efficiency of 8.0%.     

Polymer-electrolyte-based photoelectrochemical solar energy conversion with poly(3-methylthiophene) photoactive electrode

A photoelectrochemical cell based on neutral poly(3-methylthiophene) electrochemically coated on indium—tin oxide as a photoactive electrode, an amorphous poly(ethylene oxide) complexed with an I₃⁻/I⁻ redox couple as a solid polymer electrolyte, and thin transparent platinum film vapour deposited on indium—tin oxide as a counter electrode has been constructed. At catholic potentials a cathodic photocurrent was obtained indicating that the neutral poly(3-methylthiophene) is a p-type semiconductor. The short-circuit current and open-circuit voltage obtained with white light illumination at 100 mW cm⁻² are 0.35 μA cm⁻² and 140 mV, respectively. The monochromatic photon to current conversion efficiency obtained under illumination through back and front side is 0.3 and 0.6%, respectively. Studies of the photocurrent action spectra revealed that the poly(3-methylthiophene)/solid polymer electrolyte junction is responsible for the photocurrent generation. The intensity and time dependence of the short-circuit current and open-circuit voltage have been studied.     

A phenylenevinylene copolymer with perylene bisimde units as organic sensitizer for dye-sensitized solar cells

An alternating phenylenevinylene copolymer P with perylene bisimide units has been used as organic sensitizer to fabricate dye-sensitized solar cells (DSSCs) based on porous and TiCl₄ modified TiO₂ photoelectrodes. As a consequence of the compact layer formed by TiCl₄ treatment to the porous TiO₂ thin film layer, an efficient electron network was formed. Dark current measurements and electrochemical impedance spectra (EIS) suggested that modified photoelectrode significantly reduced the recombination rate of electrons with redox couple in the electrolyte due to the reduced bare FTO surface and longer electron lifetime as compared to the porous TiO₂ photoelectrode. The power conversion efficiency of DSSCs utilizing this copolymer as sensitizer is about 2.60% and 3.98% with porous and modified TiO₂ photoelectrodes, respectively.     

Photovoltaic performance of quasi-solid state dye sensitized solar cells based on perylene dye and modified TiO2 photo-electrode

The influence of compact layer of TiO₂ between FTO and nano-porous TiO₂ on the charge transport and photovoltaic properties of quasi-solid state dye sensitized solar cells with polymer gel electrolyte and perylene derivative dye as sensitizer was investigated. The PEDOT:PSS/graphite/FTO was used as counter electrodes for present investigation. The modification of photo-electrode significantly improve the power conversion efficiency (2.94%) of the solar cells attributed to the higher electron lifetime and reduction in recombination processes as indicated by the electro-chemical impedance spectra of the solar cell. The compact layer provide a large TiO₂/FTO contact area, reduce the electron recombination by blocking the direct contact with the redox couple in the electrolyte and efficient collection of electrons by FTO electrode. Finally, the incorporation of TiO₂ nano-particle in the polymer electrolyte further improves the power conversion efficiency (3.2%) of the device attributed to the improved ion transport.     

Effects of surface-modified photoelectrode on the power conversion efficiency of dye-sensitized solar cells

The effects of Na₂SO₄ as a surface modification material on the performance of dye-sensitized solar cells (DSSCs) were studied. The surfaces of TiO₂ films were firstly modified with aqueous Na₂SO₄ solution by a dip coating process, and then the resulting electrode was applied to the photoelectrode of a DSSC. The DSSC with the Na₂SO₄-modified photoelectrode had a power conversion efficiency of 9.01% compared with that (7.97%) of the reference cell, which corresponds to an increase of about 13.0% in the efficiency due to an enhancement in short-circuit current (J _sc ) and open-circuit voltage (V _oc ). A series of measurements such as UV-visible absorption, electrochemical impedance, incident photon to current conversion (IPCE) efficiency and dark current revealed that incorporation of Na₂SO₄ onto the TiO₂ film led to an increase of dye adsorption and a longer lifetime of electrons injected from dyes to the TiO₂ electrodes, resulting in the improvement in both J _sc and V _oc , compared to those of a reference device without surface modification.     

Highly efficient and stable dye-sensitized solar cells from adding low melting point glass frits

TiO₂ films were modified by adding a low melting point glass frit as a light scattering particle and applied to an anode electrode in dye-sensitized solar cells (DSSCs) to enhance the interconnection between TiO₂ and fluorine doped transparent oxide. The optical properties, photovoltaic properties and microstructures of the photo electrodes were examined to determine the role of the low glass transition temperature (T_g) glass frit. Electrochemical impedance spectroscopy, the Brunauer-Emmett-Teller method and a scratch test were conducted to support the results. The DSSC with the TiO₂ film containing 3 wt% low T_g frit showed optimal performance (5.1%, efficiency) compared to the TiO₂-based one. The photocurrent density slightly decreased by adding 3 wt% low T_g frit due to its large size and non-conductivity. However, the decrease of current density was compensated for by the scattering effect, high surface area and low electron transfer impedance at the electrolyte-dye-TiO₂ interface.     

Effect of process parameters on the efficiency of dye sensitized solar cells

The impact of process parameters on the efficiency of dye-sensitized solar cell (DSSC) was studied in order to improve its performance. TiO₂ working electrodes were prepared on FTO glass for various TiO₂ mixing time. Also these electrodes were sintered at four different temperatures (400, 450, 500, and 550°C) for one hour in ambient atmosphere. Platinum-sputtered counter electrodes were prepared at different light transmittance (70, 50, 30, and 0%). Microstructural charecterization of these electrodes were studied by X-ray diffraction method (XRD) and Scanning electron microscope (SEM). I–V characteristics of DSSCs made up of different working and counter electrodes were studied using solar simulator. Maximum efficiency (open circuit voltage (V_oc)∼0.68 V and short-circuit current density (J_sc) ∼ 12.3 mA/cm²) was observed for DSSC consisting of TiO₂ working electrode (12h mixing time, 500°C sintering temperature) and 0% transmittance Pt counter electrode. These results indicate that enhancement possibility of overall performance in DSSC was obtained by controlling process parameters, especially TiO₂ mixing time, sintering temperature and counter electrode transmittance.     

Effect of the thickness of the Ru-coating on a counter electrode on the performance of a dye-sensitized solar cell

A ruthenium (Ru) catalytic layer was assessed as the counter electrode (CE) in dye sensitized solar cells (DSSCs) by examining the effect of the Ru thickness on the DSSC performance. Ru films with different thicknesses (34, 46, 69 and 90 nm) were deposited on glass/fluorine-doped tin oxide (FTO) substrates as the CE by atomic layer deposition (ALD) at 250 °C using RuDi as the precursor and O₂ as the reaction gas. Finally, a 0.45 cm² DSSC of glass/FTO/TiO₂/dye(N719)/electrolyte(C6DMII, GSCN)/Ru CE structure was prepared. The properties of the DSSCs were examined by field emission scanning electron microscopy (FESEM), four-point-probe, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), current-voltage (I–V), incident photon-to-current conversion efficiency (IPCE), and dark current measurements. FESEM showed that the crystallized Ru films had been deposited quite uniformly and conformally on the glass/FTO surface. The sheet resistance of the Ru film decreased with increasing Ru thickness. CV profiling revealed an increase in catalytic activity with increasing film thickness. The charge transfer resistance at the interface between the Ru-coated CE and electrolyte decreased with increasing Ru thickness. I–V profiling showed that the energy conversion efficiency was increased up to 3.40 % by increasing the Ru thickness. Moreover, the IPCE and dark current results showed the efficiency of the Ru-coated CE was comparable to that of a conventional platinum (Pt) CE.     

Solid-state photoelectrochemical device using poly(o-methoxy aniline) as sensitizer and an ionic conductive elastomer as electrolyte

We report on a photoelectrochemical cell based on polymers (electrolyte and sensitizer) and TiO₂. Poly(epichlorohydrin-co-ethylene oxide) filled with NaI/I₂ was used as electrolyte and poly(o-methoxy aniline) doped with p-toluenesulfonic (PoAni-TSA) as dye. The short-circuit current and open-circuit voltage obtained with illumination at 120 mW cm⁻² are 12.2 μA cm⁻² and 0.048 V, respectively, indicating that the ionic conductive elastomer is appropriated for assembling a totally solid device. The monochromatic photon-to-current conversion efficiency decreases from 1.3% to 0.1%, from 410 to 600 nm, respectively, showing that the conducting polymer acts as a dye for TiO₂, injecting electrons into its conduction band.     

Preparation of doping metal TiO2 particle/nanotube composite layer and their applications in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) are composed of a dye-adsorbed nanoporous TiO₂ layer on a fluorinedoped tin oxide (FTO) glass substrate, redox electrolytes, and a counter electrode. DSSCs are constructed through the application of nano-metals and TiO₂ nanoparticle/TiO₂ nanotube (TNT) composite particles with various compositions. The use of oxide semiconductors in the form of nanorods, nanowires, and nanotubes is an interesting approach to improve electron transport through the film. In addition, a suitable amount of TNT in the film could provide a large surface area for the adsorption of the dye. A nano-metal is proposed, wherein the conduction band (CB) prohibits the trapping effects of electrons within the TiO₂ conduction band. This result is attributed to the prevention of electron recombination between the electrons in the TiO₂ conduction band with dye or electrolytes. A TiO₂ composite layer was coated onto FTO glass using a screen-printing method. The dye-sensitized solar cells were fabricated using N719 ruthenium (II) dye and I₃/I₃ ^? electrolyte. The impedance results indicate improved electron transport at the TiO₂/dye/electrolyte interface. The DSSC based on the Fe₂O₃/TiO₂/TNT composite particle hybrids exhibits better photovoltaic performance than the cell made from only TiO₂ nanoparticles.     

Enhancement of light harvesting in dye-sensitized solar cells by using Först-type resonance energy transfer

The improvement of solar energy-to-electricity conversion efficiency has continued to be an important research area for various solar cell devices. The fluorescence material was adsorbed on the TiO₂ photo-electrode with sensitizers in dye-sensitized solar cell (DSSC) to enhance the photon-to-current efficiency. The improved light harvesting efficiency which was achieved by the judicious choice/design of fluorescence material and sensitizing dyes enhances the photovoltaic performance of the DSSCs with the Först-type resonance energy transfer (FRET). The energy acceptor (N719) should absorb the fluorescence emitted from the energy acceptor on the photo-electrode surface which could enhance the light harvesting property of sensitizer in DSSC. We achieved the significant enhancement of short circuit current density (J _sc ) in DSSC by the FRET system on the photo-electrode surface. The photovoltaic performance of DSSCs containing FRET system was observed with I-V curve and incident photon-to-current efficiency. The electrical property and electron life time of DSSC was measured by using the impedance measurement method.     

Preparation and characterization of polyaniline film on stainless steel by electrochemical polymerization as a counter electrode of DSSC

Polyaniline (PANI) films were electrodeposited on stainless steel 304 (SS) from 0.5 M H₂SO₄ solution containing 0.3 M aniline by potentiostatic techniques to prepare a low cost and non-fragile counter electrode in dye-sensitized solar cell (DSSC). The compact layer, micro-particles, nanorods and fibrils were observed on the top of PANI films with different applied potentials (E_appl) by SEM. Then the conductivity and electrochemical test illuminated that a polyaniline film with the highest conductivity and best electrocatalytic activity for I₃^?/I^? reaction was electrodeposited at 1.0 V E_appl. Finally, the photoelectric measurement showed that the energy conversion efficiency of DSSC with the PANI electrode was increased with the E_appl decreasing. And the efficiency of DSSC with PANI counter electrode at 1.0 V was higher than that with Pt electrode, owing to the loosely porous structure, high conductivity and excellent catalytic activity of PANI electrode.     

Cascade structure of TiO2/ZnO/CdS film for quantum dot sensitized solar cells

Quantum dot sensitized solar cells based on cascade structure of TiO₂/ZnO/CdS electrode and polysulfide electrolyte were fabricated. The ZnO layer was deposited on screen-printed TiO₂ layer by ultrasonic spray pyrolysis method. The structure, morphology and impedance of TiO₂/ZnO film photoanode and the photovoltaic performance of TiO₂/ZnO/CdS cell were investigated. It is found that the short circuit current density and conversion efficiency are significantly improved by the introduction of ZnO layer into TiO₂/CdS film. A power conversion efficiency of about 1.56% has been obtained for TiO₂/ZnO/CdS cell, which is about 57% higher than that for TiO₂/CdS cell (0.99%). The formation of an inherent energy barrier between TiO₂ and CdS films and the passivation of surface traps on the TiO₂ film caused by the introduction of ZnO layer, which reduces the charge recombination and favors the electron transport, should be mainly responsible for the performance enhancement of TiO₂/ZnO/CdS cell.     

氢化TiO2纳米棒的制备及其对Q235碳钢的光生阴极保护特性

随着海洋开发的逐步推进,海洋工程中的金属防腐蚀问题显得愈加重要。目前,可利用半导体的光电效应实现对金属的光生阴极保护,为改善常用的TiO₂光电极材料的弱光吸收和低转换效率问题,文中利用水热法在FTO导电玻璃表面构建一维有序TiO₂纳米棒阵列,并通过氢化处理提高TiO₂对太阳光的吸收和光电流密度。考察了氢化TiO₂纳米棒阵列在海水环境下对Q235碳钢的光生阴极保护特性,结果表明氢化TiO₂纳米棒的光电流密度达到了2.12 mA/cm²,且稳定性良好;当Q235碳钢耦连于模拟太阳光照下的氢化TiO₂纳米棒电极时,其界面反应电阻变小,电极电位较原先的腐蚀电位降低约349 mV,说明氢化TiO₂纳米棒阵列能够对碳钢产生良好的光生阴极保护效应,且该效应在无光条件下能保持至少7 h。     

氧化参数对TiO_2纳米管结构及双室光电化学池产氢性能的影响

采用乙二醇电解液,在不同氧化电压、氧化时间条件下通过阳极氧化纯钛片制备了一系列TiO_2纳米管阵列薄膜。使用场发射扫描电镜(FESEM)表征TiO_2纳米管的表面、断面形貌,探讨氧化时间及氧化电压对纳米管生长速率的影响。同时通过电化学方法测试TiO_2纳米管的光电化学性能,以无外加电压下双室光电化学池中的产氢量考察其光催化活性。结果表明,相比延长氧化时间,提高氧化电压更容易获得高长/径比的TiO_2纳米管阵列,同时可显著提高TiO_2纳米管的光电流、光电转换效率及产氢量。     

Ionic liquid doped poly(N-methyl 4-vinylpyridine iodide) solid polymer electrolyte for dye-sensitized solar cell

Ion conducting polymer electrolyte, poly(N-methyl 4-vinylpyridine iodide) (PVPI) is synthesized for dye-sensitized solar cell (DSSC) application. A new solid polymer electrolyte composite containing low viscosity ionic liquid (IL) 1-ethyl 3-methylimidazolium dicyanamide (EMImDCN) doped PVPI is developed and its structural, electrical and photoelectrochemical studies are presented in detail. Fourier transform infrared (FTIR) spectroscopy, proton NMR and atomic force microscopy (AFM) affirms the modified polymer and its composite nature with porous surface morphology. The developed solid polymer electrolyte shows enhancement in ionic conductivity (σ) due to IL doping. The maximum σ value of 9.12 × 10^?6 S cm^?1 was obtained at 40 wt% IL concentration. The redox behavior of the electrolyte has been verified by the cyclic voltammetry studies. For device application, we have fabricated a DSSC using this solid polymer–IL electrolyte system which shows energy conversion efficiency of the solid-state cell as 0.65% under irradiation of simulated sunlight (AM 1.5, 100 mW cm^?2).     

堇青石表面化学气相沉积二氧化钛的负载机理及负载动力学

以酸蚀改性堇青石为基体,利用化学气相沉积法（CVD）在基体上负载TiO₂,采用扫描电子显微镜、能谱仪、X射线衍射仪、BET比表面积法等对负载了TiO₂的堇青石进行表征,测定不同温度下的负载速度。结果表明：负载了TiO₂的堇青石主要由（211）及（200）取向的锐钛矿TiO₂组成,呈八面体和立方体形态,BET比表面积达78.80 m²·g^-1,平均孔径为9.80 nm,具有双峰分布特征。负载过程为TiCl₄及O₂向堇青石基体扩散吸附,TiCl₄分解为Ti⁴⁺并在高氧势下进入基体晶格形成TiO₂晶核,并经过择优取向和外延式生长,其负载沉积速率方程为,其中T为负载温度,为气相TiCl₄的分压。     

Two-dimensional X-shaped organic dyes bearing two anchoring groups to TiO2 photoanode for efficient dye-sensitized solar cells

Novel two-dimensional X-shaped donor–π–acceptor (D–π–A)-type dyes were designed and successfully synthesized for use in a dye-sensitized solar cell (DSSC). Two triphenylamine units in these dyes act as electron donor units, while two cyanoacrylic acid groups act as electron acceptor units and anchoring groups to the TiO₂ photoanode. The photovoltaic properties of the newly synthesized dye-containing DSSCs were investigated to identify the effects of conjugation length between the electron donors and acceptors, and the molecular energy levels of the dyes. Among the three dyes we synthesized, (2E,2′E)-3,3′-(5′,5″-(4,5-bis(4-(bis(4-tert-butylphenyl)amino)styryl)-1,2-phenylene)bis(2,2′-bithiophene-5′,5-diyl))bis(2-cyanoacrylic acid) (11) showed the highest power conversion efficiency of 3.14% (η_max = 4.06% with TiCl₄ treatment) under AM 1.5G illumination (100 mW cm⁻²) in a photoactive area of 0.418 cm² with short circuit current density of 7.27 mA cm⁻², open circuit photovoltage of 612 mV, and a fill factor of 70.6%.