Mesoporous TiO<Subscript>2</Subscript> microspheres synthesized via a facile hydrothermal method for dye sensitized solar cell applications

Mesoporous TiO₂ microspheres were successfully synthesized by a facile hydrothermal process and the obtained product was sintered at 450 °C. The sintered TiO₂ powder was characterised by powder X-ray diffraction pattern and the result shows pure anatase phase with good crystalline nature. The morphological image of field emission scanning electron microscopy and high resolution transmission electron microscopy shows spherical shape and size of the particles is around 100 to 300 nm. The Brunauer–Emmett–Teller surface area of synthesized TiO₂ material was 56.32 m² g^?1 and average pore width of synthesized materials was 7.1 and 9.3 nm. Bimodal pore structure of TiO₂ microspheres has been very effective for electrolyte diffusion into photoanode in dye sensitized solar cells. The synthesized anatase TiO₂ microsphere based dye sensitized solar cells have high surface area with light scattering effect to enhance the photocurrent and conversion efficiency than the commercial P25 photoanode material. The power conversion efficiency of synthesized mesoporous TiO₂ microspheres and commercial P25 material is 4.2 and 2.7 % respectively. Therefore bimodal mesoporous anatase TiO₂ microsphere appears to be a promising and potential candidate for dye sensitized solar cells (DSSC) application.     

Air fabrication of SnO2 based planar perovskite solar cells with an efficiency approaching 20%: Synergistic passivation of multi-defects by choline chloride

Defects in the perovskite films impose a serious issue on the PCE and stability of the SnO₂ based planar perovskite solar cells (SP–PSCs). So far, most researches have focused on regulating the SnO₂/perovskite interface to improve performance. However, defect passivation of the perovskite/HTM interface is more significant and potential. Herein, the non-toxic and cheap choline chloride was performed to passivate multiple defects of the MAPbI₃/HTM interface in ambient atmosphere. An optimal PCE of 19.93% (the average PCE was 18.60%) was obtained for the passivated device. Furthermore, the effect and mechanism of choline chloride on the humid and thermal stability of the SP-PSCs was investigated in detail. The passivated device without encapsulation retained 91% of its initial efficiency after 20 days in humid environment (20 ± 5 °C, 55 ± 5% RH) and 95% of the initial value under heating for 7 cycles (85 °C). Chloride ions with smaller radius and larger electronegativity formed stronger ionic bonding with Pb²⁺ to passivate I^? vacancy defects, while choline ions passivated MA⁺ vacancies. This work not only provides guidance for fabrication of an efficient and stable device in air, but also opens an avenue to understanding of relation between stability and defects in the SP-PSCs.     

Aminosilicate modified zinc oxide Nanorod-GO nanocomposite for DSSC photoanodes

Amine-functionalized ZnO nanorods@graphene oxide (ZnO-NR/NH₂/GO) nanocomposites prepared by a facile solution route have been investigated through X-ray diffraction, diffuse reflectance spectra, Raman spectra, scanning electron microscopy and transmission electron microscopy. The amine-functionalized ZnO-NR/NH₂/GO-2 nanocomposite exhibits very strong visible light absorption. Dye-sensitized solar cell (DSSC) made of ZnO-NR/NH₂/GO-2 nanocomposite (with optimum 2 wt % GO) photoanode delivers a power conversion efficiency (PCE) of 3.76% which is much higher than the efficiency of unmodified ZnO-NR/GO photoanodes based DSSC (2.27%). The enhancement of PCE is primarily caused by the increased current density, attributed to the incorporation of aminosilicate and GO on the surface of ZnO-NRs which facilitates rapid transfer of electron from conduction band of ZnO to conducting surface of FTO. This diminished recombination of photogenerated electrons and holes improve the electron transfer at the photoanode/electrolyte interfaces.     

Enhanced electron harvesting in next generation solar cells by employing TiO2 nanoparticles prepared through hydrolysis catalytic process

Titanium dioxide (TiO₂) nanoparticles (NPs) were synthesized through solvothermal route by changing the rate of hydrolysis in the catalytic process. In order to change the hydrolysis rate, the concentration of acetic acid, as additive, was varied as 2 M, 3 M and 4 M. The synthesized NPs were examined by various physico-chemical characterization techniques. The powder X-ray diffraction (PXRD) analysis of the NPs reveals only the anatase phase of TiO_2. The spherical shaped morphology of the NPs was observed in the high-resolution transmission electron microscopy (HR-TEM) analysis. The optical behaviour such as absorption, bandgap, diffuse reflectance and photoluminescence (PL) emission of the NPs were studied. The material's nature and behaviors were scrutinized and they were employed as photoanode in dye sensitized solar cell (DSSC) and as electron transport layer (ETL) in carbon-based perovskite solar cell (C-PSC). The charge transfer at the interface of the devices was studied with electrochemical impedance spectroscopy (EIS). The fabricated DSSC and C-PSC show highest power conversion efficiency (PCE) of 6.1% and 10.6%, respectively. The highest current collection was detected in C-PSC and the results are discussed in detail.     

TiO2/CdS/CdSe quantum dots co-sensitized solar cell with the staggered-gap (type-II) heterojunctions for the enhanced photovoltaic performance

The effect of co-sensitization and ZnS passivation on the photovoltaic performance of CdS quantum dot sensitized solar cells (QDSSCs) were investigated. The deposition of CdS, CdSe quantum dots (QD) and ZnS passivation on TiO₂ photoanode was carried out by successive ionic layer adsorption and reaction (SILAR) method. CdS/CdSe co-sensitization developed two staggered type-II heterojunctions at TiO₂/CdS and CdS/CdSe interfaces and resulted a cascade energy band structure. This suitable band alignment facilitated the double charge transfer mechanism at each heterojunction and transported the electrons easily into the photoanode. The narrow bandgap sensitizers CdS and CdSe significantly improved the potential utilization of solar spectrum with more charge carrier generation. ZnS passivation on QD surface suppressed electrode/electrolyte interfacial charge recombination and facilitated more electron injection from QDs into TiO₂ photoanode. The EDAX elemental mapping results inferred that CdS, CdSe and ZnS have efficiently covered the TiO₂ surface. TiO₂/CdS and CdS/CdSe interfaces and the amorphous nature of ZnS could be verified with HRTEM images. Hence, the co-sensitization and surface passivation played a significant role to enhance the PCE of CdS QDSSC from 1.9% to 4.05%.     

TiO2–BaTiO3 nanocomposite for electron capture in dye‐sensitized solar cells

Different compositions of TiO₂–BaTiO₃ nanocomposites are synthesized with various weight ratios for dye‐sensitized solar cell (DSSC) applications. TiO₂ and BaTiO₃ nanoparticles (NPs) are synthesized by sol‐gel and solvothermal methods, respectively and are employed as the photoanode electrodes. BaTiO₃ NPs have pure cubic perovskite crystal structure with an average size of 20‐40 nm, while TiO₂ NPs show pure anatase phase with 15‐30 nm size. The power conversion efficiency (PCE) enhancement of the cells is first attained by controlling the thickness of the films for light harvesting improvement. The fabricated DSSC composed of pure BaTiO₃ NPs with an optimal thickness of 25 μm shows efficiency of 6.83%, whereas that made of pure TiO₂ NPs with 14 μm thickness has cell efficiency of 7.24%. Further improvement of cell efficiency is achieved by preparation of binary oxide nanocomposites using TiO₂ and BaTiO₃ NPs with various weight ratios. The highest PCE of 9.40% is obtained for the nanocomposite with TiO₂:BaTiO₃=85:15 (wt%). The enhancement is assigned to less recombination of photo‐generated electrons and higher incident photon to current conversion yield as a result of rapid charge collection and higher dye sensitization.     

Study of Pb-based and Pb-free perovskite solar cells using Cu-doped Ni1-xO thin films as hole transport material

SCAPS solar cell simulation program was applied to model an inverted structure of perovskite solar cells using Cu-doped Ni_1-xO thin films as hole transport layer. The Cu-doped Ni_1-xO film were made by co-sputtering deposition under different deposition conditions. By increasing the amount of the Cu-dopant, the film crystallinity enhanced whereas the bandgap energy decreased. The transmittance of the thin films decreased significantly by increasing the sputtering power of copper. High quality, uniform, compact, and pin-hole free films with low surface roughness were achieved. The structural, chemical, surface morphology, optical, electrical, and electronic properties of the Cu doped Ni_1-xO films were used as input parameters in the simulation of Pb-based (MAPbI_3-xCl_x) and Pb-free (MAGeI₃) perovskite solar cells. Simulation results showed that the performance of both Pb-based and Pb-free perovskite solar cell devices significantly enhanced with Cu-doped Ni_1-xO film. The highest power conversion efficiency (PCE) for the Pb-free perovskite solar cell is 8.9% which is lower than the highest PCE of 17.5% for the Pb-based perovskite solar cell.     

Quasi solid state dye-sensitized solar cells with modified TiO2 photoelectrodes and triphenylamine-based dye

Quasi solid state dye-sensitized solar cells (DSSCs) have been fabricated with organic sol or TiCl₄ modified TiO₂ and porous TiO₂ photoanode and a triphenylamine-based dye (TPAR3) used as photosensitizer. Dark current measurements suggested that both modified TiO₂ photoelectrodes had significantly reduced the recombination rate of photoelectrons due to the reduced bare FTO surface in comparison to porous photoelectrode. The DSSC based on modified TiO₂ photoelectrodes showed improved photovoltaic parameters compared to the porous TiO₂ photoelectrode. The overall power conversion efficiency (PCE) is 3.27%, 4.73% and 6.8% for porous, TiCl₄ modified and sol modified TiO₂ photoelectrodes, respectively. The improved PCE with modified TiO₂ electrodes was attributed to the formation of a compact layer. This effectively improves adherence of TiO₂ to FTO surface, providing a larger TiO₂/FTO contact area and reducing the electron recombination by blocking the direct contact between redox electrolyte and the conductive FTO surface and enhances the electron collection efficiency.     

Plasmonic Effects of Infiltrated Silver Nanoparticles Inside TiO2 Film: Enhanced Photovoltaic Performance in DSSCs

The plasmonic effects of infiltrated silver (Ag) nanoparticles, with different contents, inside a nanostructured TiO₂ film on the photovoltaic performance of dye‐sensitized solar cells (DSSCs) are explored. The synthesized Ag nanoparticles are immobilized onto deposited TiO₂ nanoparticles by a new strategy using 3‐mercaptopropionic acid (MPA), a bifunctional linker molecule. Transmission electron microscope (TEM) images show that monodispersed Ag and polydispersed TiO₂ nanoparticles have an average diameter of 12 ± 3 nm and 5 ± 1 nm, respectively. Moreover, Fourier transform infrared spectroscopy (FTIR) analysis reveals that Ag nanoparticles were successfully functionalized and capped with MPA. Optical studies on the MPA‐capped Ag nanoparticles inside TiO₂ film show an increase in the total absorbance of the electrode. Moreover, EIS measurements confirm that MPA‐capped Ag nanoparticles inhibit the charge recombination and improve the stability of nanoparticles in I₃^?/I^? electrolyte. The DSSC assembled with optimal content of MPA‐capped Ag nanoparticles demonstrated an enhanced power conversion efficiency (8.82% ± 0.07%) compared with the pure TiO₂ (7.30% ± 0.05%). The increase in cell efficiency was attributed to the enhanced dye light absorption in strength and spectral range due to the surface plasmon resonance of MPA‐capped Ag nanoparticles in the photoanode.     

Highly efficient photocatalytic degradation of methylene blue using carbonaceous WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> composites

Recent improvements in the performance of photocatalysts made it possible to tackle pollution through environment friendly methods. This study investigates the modification of the photocatalytic activity of TiO₂ by employing WO₃ and conductive polymers, namely, polyaniline (Pani) and polypyrrole (Ppy). Basing on our previous improvement of TiO₂ using a conductive polymer and activated carbon (AC), this study determines the activated carbon forms of TiO₂. The prepared composites are characterized using X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, Brunauer–Emmet–Teller, and UV–Vis spectroscopy. The specific surface area of the mesoporous composites is as follows: WO₃/TiO₂·AC (Pani) > WO₃/TiO₂·AC (Ppy) > WO₃/TiO₂·Pani > WO₃/TiO₂·Ppy (127 > 98 > 68 > 44 m² g^?1), which exhibited a similar trend to the photocatalytic performances (100 > 95 > 91 > 72 % conversion rate). This result could be attributed to higher porosity, surge of charge separation, and photo-responding range extension induced by the synergistic effect of WO₃, conducting polymers, and TiO₂ in the samples.     

Improved photovoltage and performance by aminosilane-modified PEO/P(VDF-HFP) composite polymer electrolyte dye-sensitized solar cells

A PEO/P(VDF-HFP) composite polymer electrolyte was modified by different amounts of NH₂-end functional silane (3-amonopropyltriethoxysilane, APTS). Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were carried out to examine the configuration changes of the polymer electrolyte. The newly formed Si-O-Si network and interactions influenced the ionic conductivity of the APTS-modified polymer electrolyte and also enhanced the connection of the polymer electrolyte with the electrodes of the dye sensitized solar cells (DSSCs). The cyclic voltammograms and electrochemical impedance measurements indicated that the APTS deprotonated the TiO₂ photoanode surface and negatively changed the Fermi energy level and the conduction band edge to the vacuum level. This effectively reduced the interface recombination in the DSSC and improved the open circuit voltage. With moderate APTS content (0.1 M) modification, the DSSC exhibited a 58 mV improvement of photovoltage and an improved performance of 5.08% compared with 3.74% of the original DSSC.     

QUASI-SOLID-STATE DYE-SENSITIZED SOLAR CELLS BASED ON ZnO PHOTOANODE

ZnO photoanode in dye-sensitized solar cells (DSSCs) has been successfully prepared by the electro-hydrodynamic (EHD) technique. The sandwich solar cells exhibited a short-circuit photocurrent density of 7.0 mA cm^?2 and conversion efficiency of 1.65% with a quasi-solid-state electrolyte under simulated sun illumination (AM-1.5, 100 mW cm^?2). The stability and the influencing factors, such as film thickness and light intensity, on solar cell performance were discussed.     

Formation of nanotubes in poly (vinylidene fluoride): Application as solid polymer electrolyte in DSC fabricated using carbon counter electrode

In the present work, we report the incorporation of 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) in poly(vinylidene fluoride) (PVDF) along with the redox couple (I⁻/I₃⁻). When ABTS, a π-electron donor, is used to dope PVDF, the polymer composite forms brush-like nanotubes and has been successfully used as a solid polymer electrolyte in dye-sensitized solar cells. Under the given conditions, the electrolyte composition forms nanotubes while it is doped with ABTS, a π-electron donor. With this new electrolyte, a dye-sensitized solar cell was fabricated using N3 dye adsorbed over TiO₂ nanoparticles as the photoanode and conducting carbon cement coated FTO as counter electrode.     

Double‐Layer Structure Photoanode with TiO2 Nanotubes and Nanoparticles for Dye‐Sensitized Solar Cells

Here, we report a novel double‐layer structure photoanode with TiO₂ nanotube (TNT) layer and TiO₂ nanoparticle (TP) layer via a two‐step method of electrochemical anodization and screen printing for dye‐sensitized solar cells (DSSCs). The results indicate that DSSCs with this double‐layer structure have significant advantages of large surface area, long electron lifetime, superior electron recombination restraint characteristics, and high light scattering. The layer thickness of nanotubes and nanoparticles is also investigated and finally an optimized double‐layer structure with excellent performance is prepared. With such a double‐layer structure photoanode, DSSC with a relative high conversion efficiency of 6.43% and a short‐circuit photocurrent density of 16.40 mA·cm^?2 is obtained.     

Fabrication of Three-Dimensionally Ordered Macroporous TiO2 Films with Enhanced Photovoltaic Conversion Efficiency

Negative-charged polystyrene (PS) microspheres were prepared through a soap-free emulsion polymerization method using potassium persulfate as initiator. Three-dimensionally ordered macroporous TiO₂ films were fabricated using the high-quality PS colloidal crystals templates obtained via a horizontal deposition method. The as-prepared macroporous TiO₂ films were applied as the photoanodes in dye-sensitized solar cell (DSSC). The microstructure of the products were characterized by X-ray diffractometer, fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption–desorption analyzer. The results showed that the macroporous TiO₂ films replicated well the 3D ordered structure derived from PS colloidal crystal templates and revealed a relatively large specific surface area (69.99 m²/g), which could increase the capacity of TiO₂ film anode for absorbing dyes and scattering light. The photocurrent–voltage (I–V) characteristics of DSSC were measured by a digital source meter under simulated solar light. The results indicated that the introduction of an ordered macroporous TiO₂ interfacial layer increased the photovoltaic conversion efficiency, which was improved by 68 % from 3.61 to 6.08 %, as compared to a device using a bare P25 TiO₂ photoanode. Our results showed that the hierarchically ordered macroporous TiO₂ bilayer films photoanode for DSSC could be helpful to improve the photovoltaic conversion efficiency.     

Dependence of the electrocatalytic performance of platinized counter electrodes on the redox mediator employed in dye-sensitized solar cells

The electrocatalytic properties of platinized counter electrodes (Pt CEs) prepared by various coating methods were investigated with respect to the redox mediator, including the widely used iodide/tri-iodide (I^?/I ₃ ^? ) and the more recently introduced cobalt(II/III)tris(2,2′-bipyridine) (Co(bpy) ₃ ^2+/3+ ), for application in dye-sensitized solar cells (DSCs). The coating methods controlled Pt loading and the surface morphology of the Pt CEs. For a high-performance DSC with a fill factor >0.7, the charge-transfer resistance at the Pt CE/electrolyte interface should be <4.5 Ω cm² for both redox mediators. The I^?/I ₃ ^? -mediated DSCs were insensitive to Pt loading as low as 0.001 mg cm^?2, while the Co(bpy) ₃ ^2+/3+ -mediated DSCs required relatively large Pt loadings of > 0.005 mg cm^?2. Our results indicated that care should be taken in the preparation of Pt CEs with high transparency and low loading to obtain high-performance DSCs employing cobalt–ligand redox electrolyte.     

A natural tomato slurry as a photosensitizer for dye-sensitized solar cells with TiO2/CuO composite thin films

We have studied the performance of dye-sensitized solar cells by employing natural dye “anthocyanins” extracted from the tomato slurry as a sensitizer for the TiO₂/CuO photoanode. The extracts were anchored on TiO₂/CuO films deposited on an ITO substrate which was used as a photoanode. The dye adsorbed TiO₂/CuO films electrode, the copper plate as a counter electrode, and iodolyte as an electrolyte were assembled into DSSCs. The conversion efficiency of the DSSCs was found to be 2.96% with a V_OC of 0.615 V, J_SC of 6.6 mA/cm², and an FF of 0.73. This work highlights the use of contribution of the tomato slurry as a natural sensitizer to enhance the efficiency of DSSCs.     

钙钛矿太阳能电池中D-A-D型空穴传输材料的研究进展

钙钛矿太阳能电池(Perovskite Solar Cells, PSCs)作为一种新型太阳能电池,由于其短时间内快速提升的光电转换效率而获得了全世界范围内的广泛关注。空穴传输材料(Hole Transporting Materials, HTM)是钙钛矿太阳能电池的重要组成部分,因此,设计开发经济、高效、稳定的HTM对PSCs的发展具有重要意义。本文综述了2009年以来线型给体-受体-给体(Donor-Acceptor-Donor, D-A-D)结构有机小分子空穴传输材料在PSCs中的应用,详细介绍了各空穴传输材料分子结构对PSCs的光电转换效率和器件稳定性等性能的影响。在此基础上,对未来线型D-A-D型空穴传输材料的发展进行了展望。     

Effect of silver (Ag) ions irradiation on the structural,optical and photovoltaic properties of Mn doped TiO2 thin films based dye sensitized solar cells

Dye sensitized solar cell (DSSC) is an emerging energy harvesting tool which converts direct sunlight into electrical energy. These cells have much better properties in contrast with silicon based solar cells because of their flexible nature, light weight, low cost, environment friendly nature, and involvement of a simple manufacturing process. Since, a photoanode is the backbone of DSSC, we synthesized a pure and 1% manganese (Mn) doped titanium dioxide (TiO₂) films by sol-gel method which are irradiated with silver (Ag) ions at two different concentrations (2 × 10¹⁴ and 4 × 10¹⁴) ions-cm^?2. X-ray diffraction revealed that Mn doping followed by Ag irradiation transformed TiO₂ from pure anatase to rutile phase. Ultraviolet–visible spectroscopy exposed the reduction in band gap of TiO₂ film during this doping and irradiation process. Therefore, absorption is enhanced with red shift in UV-range. When these films are used as a photoanode in DSSC, 1% Mn doped TiO₂ film exposed with Ag at the concentration of (2 × 10¹⁴) ions-cm^?2 exhibited maximum efficiency of 2.40%.     

Optimization of TiO2 paste concentration employed as electron transport layers in fully ambient air processed perovskite solar cells with a low-cost architecture

The optimization of thickness and surface roughness of the TiO₂ layer as an efficient electron transporting layer (ETL) plays a significant role on the performance improvement of perovskite solar cells (PSCs). In the present investigation, TiO₂ pastes synthesized with various concentrations under hydrothermal conditions were utilized to deposit the TiO₂ films of tunable porosities as the ETLs of PSCs. Also, the PSCs were fabricated with a structure of FTO/block-TiO₂ (b-TiO₂)/m-TiO₂/CH₃NH₃PbI₃ (MAPbI₃)/CuInS₂ (CIS)/carbon as a low-cost architecture. Moreover, the effect of the TiO₂ paste concentration was studied on the performances of PSCs under fully ambient conditions. The optimal TiO₂ layer was constructed with 20 wt% TiO₂ paste concentration, which resulted in the formation of a hole‐free, smooth, and compact ETL layer. The champion perovskite solar cell fabricated with the 20 wt% TiO₂ paste concentration showed the highest power conversion efficiency (PCE) of 13.09% (J_SC = 20.80 mA cm^?2, V_OC = 0.98 V and FF = 0.64) but the champion PSC device made with the 10 wt% TiO₂ paste exhibited the lowest PCE = 8.05% (J_SC = 19.83 mA cm^?2, V_OC = 0.91 V and FF = 0.45). These results illustrated that the optimal 20 wt% TiO₂ paste caused ～163% enhancement in the PCE of the device. Consequently, it could be suggested for application in fabrication of cost-effective and large scale PSCs.