Improved conversion efficiency in dye-sensitized solar cells based on electrospun Al-doped ZnO nanofiber electrodes prepared by seed layer treatment

The application of electrospun nanofibers in electronic devices is limited due to their poor adhesion to conductive substrates. To improve this, a seed layer (SD) is introduced on the FTO substrate before the deposition of the electrospun composite nanofibers. This facilitates the release of interfacial tensile stress during calcination and enhances the interfacial adhesion of the AZO nanofiber films with the FTO substrate. Dye-sensitized solar cells (DSSC) based on these AZO nanofiber photoelectrodes have been fabricated and investigated. An energy conversion efficiency (η) of 0.54-0.55% has been obtained under irradiation of AM 1.5 simulated sunlight (100 mW/cm²), indicating a massive improvement of η in the AZO nanofiber film DSSCs after SD-treatment of the FTO substrate as compared to those with no treatment. The SD-treatment has been demonstrated to be a simple and facile method to solve the problem of poor adhesion between electrospun nanofibers and the conductive substrate.     

Effect of clay on the corrosion protection efficiency of PMMA/Na-MMT clay nanocomposite coatings evaluated by electrochemical measurements

The preparation of PMMA-clay nanocomposites was investigated by using sodium dodecylbenzenesulfonate (SDS) and potassium peroxodisulfate (KPS) as a surfactant and chain initiator for an in situ emulsion polymerization reaction, respectively. The as-prepared nanocomposites were then characterized by Fourier transformation infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXRD) patterns and transmission electron microscopy (TEM).It should be noted that the nanocomposite coating containing 1 wt% of clay loading was found to exhibit an observable enhanced corrosion protection on cold-rolled steel (CRS) electrode at higher operational temperature of 50 °C, which was even better than that of uncoated and electrode-coated with PMMA alone at room temperature of 30 °C based on the electrochemical parameter evaluations (e.g., E_corr, R_p, I_corr, R_corr and impedance). In this work, all electrochemical measurements were performed at a double-wall jacketed cell, covered with a glass plate, through which water was circulated from a thermostat to maintain a constant operational temperature of 30, 40 and 50 ± 0.5 °C. Moreover, a series of electrochemical parameters shown in Tafel, Nyquist and Bode plots were all used to evaluate PCN coatings at three different operational temperatures in 5 wt% aqueous NaCl electrolyte. The molecular barrier properties at three different operational temperatures of PMMA and PCN membranes were investigated by gas permeability analyzer (GPA) and vapor permeability analyzer (VPA). Effect of material composition on the molecular weight and optical properties of neat PMMA and PCN materials, in the form of solution and membrane, were also studied by gel permeation chromatography (GPC) and UV-vis transmission spectra.     

Preparation of lead and tin oxide thin films by spin coating and their application on the electrodegradation of organic pollutants

In this work, lead and tin oxide films (Pb _x O _y /SnO₂) were prepared, using the spin coating technique. The influence of the temperature and duration of the thermal treatment on the final film composition were analysed. The metallic oxide films that were prepared, Pb _x O _y /SnO₂, were characterized by means of XRD, SEM/EDS and cyclic voltammetry. When different experimental preparation conditions were used different lead oxide phases were obtained. The electrochemical studies show that the films are stable and can be used as electrodes. Finally the films were tested as electrodes for the electrochemical degradation of a CHCl₃ aqueous solution.     

Parametric simulation of the back-surface field effect in the silicon solar cell

Recombination of minority carriers in the solar cell is a major contributing factor in the loss of quantum efficiency and cell power. While the surface recombination is dealt with by depositing a passivation layer of SiO₂ or SiN_x, the bulk recombination is minimized by use of nearly defect-free monocrystalline substrate. In addition, the back-surface field (BSF) effect has been very useful in aiding the separation of free electrons and holes in the bulk. In this study, the key BSF parameters and their effect on the performance of a typical p-type front-lit Si solar cell are investigated by use of Medici, a 2-dimensional device simulator. Of the parameters, the doping concentration of the BSF layer is found to be most significant. That is, for a p-type substrate of 1 × 10¹⁴ cm⁻³ acceptor concentration, the optimum doping concentration of the BSF layer is 1 × 10¹⁸ cm⁻³ or more, and the maximum cell power can be increased by 24%, i.e., 25.4 mW cm⁻² vs. 20.5 mW cm⁻², by using a BSF layer with optimum doping. With regards to the BSF layer thickness, the impact is less. That is, the maximum cell power is about 11% higher at 100 μm than at 5 μm, which translates to an increase of 1.2% μm⁻¹. In practice, therefore, it would be better to rely on the control of the doping concentration than the thickness in maximizing the BSF effect in real Si solar cells.     

Mini review on the performance of Schiff base and their metal complexes as photosensitizers in dye-sensitized solar cells

Abstract

For the requirement of clean and efficient energy, research toward the improvement of solar energy is increased because it directly converts the sunlight into electrical energy leaving no harmful effect on the environment. Dye-sensitized solar cells (DSSCs) are one of the best alternative approaches to conventional solar cells. The photosensitizer is one of the important components in DSSC and plays a key role to initiate the electrochemical process for electricity production by harvesting visible light. The power conversion efficiency of DSSC is typically based on the dye/sensitizer which is coated on the porous semiconductor TiO₂ film. Schiff base metal complexes have potential photosensitizing behavior, due to their photophysical properties. This article presents the current development attained in the designing and synthesis of Schiff base metal complexes and their application as photosensitizers and also co-sensitizers in dye-sensitized solar cells, and recent developments on the DSSC using Schiff based metal complexes.     

Application of ZnO nanoparticles to enhance photoluminescence in porous silicon and its possible utilization for improving the short wavelength quantum efficiency of silicon solar cell

We have formed photoluminescent porous silicon (PS) layers and over which a ZnO layer (hereafter called ZnOPS layers) is deposited. We studied the photoluminescent properties of individual layers as well as the composite layer under excitation with 405 nm wavelength. Using the data of PL a theoretical analysis of a solar cell having such a composite layer of a given photoluminescent conversion efficiency η_PL on the front surface has been done. The condition of a photoluminescent composite layer (ZnOPS) useful for enhancing the spectral response of n⁺-p-p⁺ structured silicon solar cell has been identified.     

Enhanced efficiency of ternary organic solar cells by doping a polymer material in P3HT:PC61BM

Doping a low‐bandgap polymer material (PDTBDT‐DTNT) as a complementary electron donor in poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁‐butyricacid methyl ester (PC₆₁BM) blend is experimented to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The PCE of OSCs was increased from 3.19% to 3.75% by doping 10 wt% PDTBDT‐DTNT, which was 17.55% higher than that of the OSCs based on binary blend of P3HT:PC₆₁BM (host cells). The short‐circuit current density (J_sc) was increased to 10.11 mA·cm⁻² compared with the host cells. Although the PCE improvement could partly be attributed to more photon harvest for complementary absorption of 2 donors by doping appropriate PDTBDT‐DTNT, the promotion of charge separation and transport as well as the suppression of charge recombination due to a matrix of cascade energy levels is also important. And the better morphology of the active layer films is beneficial to the optimized performance of ternary devices.     

Enhancement of thermal,mechanical and barrier properties of EVA solar cell encapsulating films by reinforcing with esterified cellulose nanofibres

Solar cell encapsulating film based on ethylene vinyl acetate copolymer (EVA) was modified by using bacterial cellulose (BC) nanofibres. Bacterial cellulose was chemically modified with propionic anhydride prior to compounding with EVA in a twin screw extruder. The effects of fibre content on the mechanical, thermal, optical and barrier properties of the EVA composite films were investigated. Better mechanical and barrier properties of the EVA films were obtained when the modified BC nanofibres were used. The results were ascribed to the different chemical functional groups on the fibre surface, as verified by FTIR spectra. Deacetylation of the EVA was delayed and visible light transparency of the EVA films above 75% was retained. Overall, our study showed that it was possible to improve the barrier properties of EVA film without sacrificing much transparency by using a suitable type and content of cellulose nanofibres.     

Synthesis of nano-TiO2 assisted by diethylene glycol for use in high efficiency dye-sensitized solar cells

The performance of dye-sensitized solar cells(DSSCs) consisting of anatase TiO_2 nanoparticles that were synthesized via a hydrothermal method was studied.The synthesized TiO_2 nanoparticles were characterized by X-ray diffraction(XRD),nitrogen sorption analysis,scanning electron microscopy(SEM),high resolution transmission electron microscopy(HRTEM),and UV-vis spectroscopy.Then the J-Vcurve,electrochemical impedance spectroscopy(EIS),and open-circuit voltage decay(OCVD) measurement were applied to evaluate the photovoltaic performance of DSSCs.Compared with the commercial TiO_2nanoparticles(P25),the synthesized-TiO_2 nanoparticles showed better performance.By adding diethylene glycol(DEG) before the hydrothermal process,the synthesized TiO_2 nanoparticles(hereafter referred to as TiO_2-DEG particles) shows narrower size distribution,larger specific surface area,higher crystallinity,and less surface defects than TiO_2(DEG free) particles.The analysis of photovoltaic properties of DSSCs based on TiO_2-DEG particles showed that the recombination of electron-hole pairs was decreased and the trapping of carries in grain boundaries restrained.It was believed that the photoelectrode fabricated with the as-prepared TiO_2 nanoparticles improved the loading amount of dye sensitizers(N719).and enhanced the photocurrent of the DSSCs.As a result,the TiO_2-DEG particle based cells achieved a photo-to-electricity conversion efficiency(η) of 7.90%,which is higher than 7.53%for the cell based on TiO2(DEG free) and 6.59%for the one fabricated with P25.     

A new quinoxaline and isoindigo based polymer as donor material for solar cells: Role of ecofriendly processing solvents on the device efficiency and stability

A new semiconducting polymer based on two different electron deficient (quinoxaline and isoindigo) and electron rich (benzodithiophene) moieties is synthesized, characterized and used as donor material for photovoltaic devices. Blade‐coated bulk heterojunction solar cells are fabricated in air by using chlorinated (o‐dichlorobenzene) and nonchlorinated (o‐xylene) solvents for the deposition of the active layer. The use of o‐xylene allows a ～10% improvement of the device efficiency in comparison to the analogous system processed from o‐dichlorobenzene. In addition, the evolution of the photovoltaic parameters of the resulting devices during thermal stress is monitored and compared, demonstrating a nearly identical resistance against temperature. The reported results not only highlight the promising properties of the new polymer in terms of environmental stability and compatibility with nonhalogenated solvents, but also show an easy and ecofriendly way to further improve the device performance without altering the corresponding thermal stability. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 234–242     

Preparation and properties of inhalable nanocomposite particles: effects of the size, weight ratio of the primary nanoparticles in nanocomposite particles and temperature at a spray-dryer inlet upon properties of nanocomposite particles

Nanoparticles are expected to be applicable to inhalation as carrier but there exist disadvantages because of their size. Their deposition dose to the lung will be small. To overcome this problem and utilize nanoparticles for inhalation, we have prepared nanocomposite particles as drug carriers targeting lungs. The nanocomposite particles are prepared as drug-loaded nanoparticles–additive complex to reach deep in the lungs and to be decomposed into nanoparticles when they deposit into lung. In this study, we examined the effect of preparation condition – inlet temperature, size of primary nanoparticles and weight ratio of primary nanoparticles – on the property of nanocomposite particles.

When the size of primary nanoparticles was 400 nm and inlet temperature was 90 °C, only the nanocomposite particles containing between 45 and 55% of primary nanoparticles could be decomposed into nanoparticles in water. On the other hand, when the inlet temperature was 80 °C, nanocomposite particles were decomposed into nanoparticles independent of the weight ratio of primary nanoparticles. Also, the aerodynamic diameter of the nanocomposite particles was between 1.5 and 2.5 μm, independent of the weight ratio of primary nanoparticles.

When the size of primary nanoparticles was 200 nm and inlet temperature was 70 °C, nanocomposite particles were decomposed into nanoparticles independent of the weight ratio of primary nanoparticles. Also, the aerodynamic diameters of them were almost 2.0 μm independent of the weight ratio of primary nanoparticles. When the nanocomposite particles containing nanoparticles with the size of 200 nm are prepared at 80 °C, no decomposition into nanoparticles was observed in water.

Fine particle values, FPF, of the nanocomposite particles were not affected by the weight ratio of primary nanoparticles when they were prepared at optimum inlet temperature.     

Enhancement of the efficiency of dye-sensitized solar cell with multi-wall carbon nanotubes/polythiophene composite counter electrodes prepared by electrodeposition

For the purpose of increasing the energy conversion efficiency of dye-sensitized solar cells (DSSCs), multi-wall carbon nanotube (MWCNT)/polythiophene (PTh) composite film counter electrode has been fabricated by electrophoresis and cyclic voltammetry (CV) in sequence. The morphology and chemical structure have been characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), and Raman spectroscopy respectively. The overall energy conversion efficiency of the DSSC employing the MWCNT/PTh composite film has reached 4.72%, which is close to that of the DSSC with a platinum (Pt) counter electrode (5.68%). Compared with a standard DSSC with MWCNT counter electrode whose efficiency is 2.68%, the energy conversion efficiency has been increased by 76.12% for the DSSC with MWCNT/PTh counter electrode. These results indicate that the composite film with high conductivity, high active surface area, and good catalytic properties for I₃⁻ reduction can potentially be used as the counter electrode in a high-performance DSSC.     

Influence of light scattering particles in the TiO2 photoelectrode for solid-state dye-sensitized solar cell

A TiO₂ film was modified by adding light scattering particles and applied to an anode electrode in solid-state dye-sensitized solar cells (DSSCs). The TiO₂ films with 10 wt% (vs. TiO₂ weight) light scattering particles showed enhanced performance (28%), compared with nanocrystalline TiO₂ films, which were used as the controls. In particular, the photocurrent density (J_sc) reached approximately 12.6 mA/cm² under a one-sun condition. This was attributed to the light scattering effect and decrease in internal resistance through the macroporous structure with a minor loss of electron transport. However, in the case of a larger concentration of light scattering particles (>10 wt%), there was a decrease in the efficiency of DSSCs, which resulted from the decreased surface area and degraded electron transport and charge recombination properties, as confirmed by the measurement of stepped light-induced photocurrent and photovoltage transients. Furthermore, the diffusion properties and kinetics of the composite polymer electrolyte with the nanoporous and macroporous TiO₂ films were compared and evaluated from the electrochemical impedance spectra.     

Improvement of Power Conversion Efficiency of P3HT/PCBM Polymer Solar Cell Systems by Optimization of the Process Steps

In this work, different steps involved in the fabrication of polymer solar cells were optimized using P3HT/PCBM heterojunction. Steps included spinning speed for coating of the PEDOT:PSS layer, use of filter for the PEDOT:PSS layer, spinning speed for coating of the active layer, sequence of annealing of the active layer either before or after electrode deposition, and modification of the cooling mechanism (either by cooling rapidly or slowly after heating of the active layer). Investigation of these steps led to an improvement of the power-conversion efficiency (PCE) of the polymer solar cells, especially the last step involving the change of cooling mechanism, which improved PCE by 25%.     

Push–pull effect on the geometries,electronic and optical properties of thiophene based dye-sensitized solar cell materials

Geometries, electronic structure and electronic absorption spectra of thiophene based dye-sensitized solar cells were performed using Density Functional Theory (DFT) and time dependent density functional theory (TD-DFT). Different electron donating and electron withdrawing groups have been substituted. Geometries and electronic properties have been computed at B3LYP/6-31G⁷ and absorption spectra at TD-B3LYP/6-31G⁷ level of theory. Major change in bond lengths and bond angles occurs in the system where there is electron withdrawing or electron donating groups have been substituted. In SYSTEM-2 and SYSTEM-3 intra charge transfer has been observed. HOMO of SYSTEM-2 and SYSTEM-3 is delocalized on left side while LUMO on right side of the molecule. In SYSTEM-1, HOMO is on left side while LUMO is in the center. The designed systems show two absorption peaks for each of the system. In short, choice of appropriate electron withdrawing and donating groups is very important for improving the performance of dye-sensitized solar cells.     

Stability of dye-sensitized solar cell under reverse bias condition: Resonance Raman spectroscopy combined with spectrally resolved analysis by transmittance and efficiency mapping

In this work, resonance Raman spectroscopy (RRS) together with a spectrally resolved analysis by transmittance and efficiency mapping (SATEM) have been applied as a powerful tool to detect and to understand deeply the degradation mechanisms suffered by a series-connected dye-sensitized solar cell (DSC) in a module under real working condition. When shadowing phenomena occur on the module, the shadowed cell works as a load rather than as a generator and suffers reverse bias (RB) condition that induces a progressive degradation until the complete device⬢s breakdown. The reported analysis follows the degradation processes involving both the electrolyte solution and the sensitizer during the aging time. In particular, polyiodides formation has been pointed out as crucial triiodide depletion mechanism in the electrolyte solution leading to a strong unbalance in the redox couple and to a slowdown in dye regeneration process. The final device breakdown occurs when hydrogen production within the electrolyte solution causes the breaking of the sealing and the partial electrolyte leakage from the active area. RRS demonstrated the irreversible structural changes suffered by dye molecules during this final stage by identifying the main degradation products. Finally, a spectrally resolved comparison between incident to photon current conversion efficiency (IPCE) for photo (PE) and counter electrode (CE) illumination were used, along with transmittance analysis, in order to derive detailed information about the structural modification suffered by the cell constituents. The combination between SATEM and RRS techniques exhaustively provided a deep comprehension of the DSC degradation processes by giving a route to further stabilize the devices for a feasible next commercialization.     

Influence of the bridging atom in fluorene analogue low‐bandgap polymers on photophysical and morphological properties of copper indium sulfide/polymer nanocomposite solar cells

This contribution presents the correlation between structural, morphological, and fluorescence properties as well as device performance of nanocomposite solar cells comprising two low‐band gap polymers, poly[[9‐(1‐octylnonyl)?9H‐carbazole‐2,7‐diyl]‐2,5‐thiophenediyl‐2,1,3‐benzothiadiazole‐4,7‐diyl‐2,5‐thiophenediyl] (PCDTBT) and poly[2,1,3‐benzothiadiazole‐4,7‐diyl‐2,5‐thiophenediyl(9,9‐dioctyl‐9H‐9‐silafluorene‐2,7‐diyl)?2,5‐thiophenediyl] (PSiF‐DBT) and copper indium sulfide (CIS). It shows that, in analogy to organic solar cells, the device efficiency is strongly determined by different polymer structures leading to a different packing of the polymer chains and consequently to diverse morphologies. X‐ray diffraction investigation indicates increased semicrystallinity in PSiF‐DBT compared with the nitrogen analogue PCDTBT. The photoluminescence (PL) quenching of this polymer indicates that the higher photogeneration achieved in PSiF‐DBT based films can be correlated to a favorable donor‐acceptor phase separation. Transmission electron microscopy studies of PCDTBT:CIS blended films suggest the formation of polymer agglomerates in the layer resulting in a decreased PL quenching efficiency. For the considered polymer:CIS system, the combination of these effects leads to an enhanced overall device efficiency. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2013, 51, 1400–1410