On The Scalability of Dye-Sensitized Solar Cells : Effect of Photoelectrode Area on the Photovoltaic and Charge Transport Parameters

This study is aimed to provide new insights on the scalability of dye-sensitized solar cells (DSCs). The DSCs of electrode area up to ~2 cm2 were fabricated using commercially available P25 TiO2 particles, N3 dye, and iodide/triiodide electrolyte and evaluated using voltage - current and electrochemical impedance spectroscopic measurements. The photovoltaic conversion efficiency follows a biexponential decay, the main contributor to which is the short circuit current density(JSC). Interesting features were observed in the electrochemical impedance spectra and charge transport parameters in the devices as the photoelectrode areas are increased. Results show that electrons from an area above a threshold are not collected due to varied choice of diffusion pathways. Furthermore, this study identify that area of the photoelectrode for reporting the efficiency needs to be fixed at ~0.5 cm2 for 25 nm TiO2 particles because below which it strongly vary. On the other hand, the study provides opportunities to build high efficiency dye-sensitized solar cells using the current choice of materials

Standardization of Photoelectrode Area of Dye-Sensitized Solar Cells

This study is aimed to provide new insights on the scalability of dye-sensitized solar cells (DSCs). The DSCs of electrode area up to [similar]2 cm2 were fabricated using commercially available P25 TiO2 particles, N3 dye, and iodide/triiodide electrolyte. The photovoltaic conversion efficiency follows a iexponential decay, the main contributor to which is the short circuit current density (JSC). Interesting features were observed in the electrochemical impedance spectra and charge transport parameters in the devices as the photoelectrode areas were increased. Results show that electrons from an area above a threshold are not collected due to varied choice of diffusion pathways. Furthermore, this study identifies that the area of the photoelectrode for reporting the efficiency needs to be fixed at [similar]0.5 cm2 for 25 nm TiO2 particles because below this value it strongly varies. On the other hand, the study provides opportunities to build high efficiency dye-sensitized solar cells using the current choice of materials

Plasmonic Enhancement of Photoactivity by Gold Nanoparticles Embedded in Hematite Films

Semiconducting n-type nanostructured hematite (α-Fe₂O₃) is a promising photocatalyst for solar water splitting because of its favorable band gap of 2.2 eV, low cost, and abundance in nature. However, its photoactivity is limited by the poor absorptivity and short hole diffusion length. Surface plasmon resonance (SPR) of metallic (Au, Ag, and Cu) nanostructures is known to concentrate and scatter incident light over a broad wavelength range and holds the promise of enhancing the light absorption cross section of a semiconducting material around the plasmonic structures. Herein we report enhanced photoelectrochemical (PEC) performance of a smooth chemical vapor deposited hematite film embedded with Au nanoparticles (NPs). About 3 times higher light absorption and photocurrent enhancement are obtained from thin hematite films containing Au NPs than with pristine hematite films. The plasmonic enhancement increases with the amount of Au NPs for the same thickness of hematite. Thickness-dependent study of photoactivity indicates a higher enhancement in hematite thin films compared to thicker films due to reduced charge transport distance and optimal local field enhancement effect. The improved embedded configuration also has the advantage of consistent performance and protection of plasmonic nanostructures from electrochemical corrosion, resulting in long cycles of operation

Visible Light Driven Photoelectrochemical Properties of Ti@TiO₂ Nanowire Electrodes Sensitized with Core–Shell Ag@Ag₂S Nanoparticles

We present a model electrode system comprised of nanostructured Ti electrode sensitized with Ag@Ag₂S core–shell nanoparticles (NPs) for visible light driven photoelectrochemistry studies. The nanostructured Ti electrode is coated with Ti@TiO₂ nanowires (NW) to provide a high surface area for improved light absorption and efficient charge collection from the Ag@Ag₂S NPs. Pronounced photoelectrochemical responses of Ag@Ag₂S NPs under visible light were obtained and attributed to collective contributions of visible light sensitivity of Ag₂S, the local field enhancement of Ag surface plasmon, enhanced charge collection by Ti@TiO₂ NWs, and the high surface area of the nanostructured electrode system. The shell thickness and core size of the Ag@Ag₂S core–shell structure can be controlled to achieve optimal photoelectrochemical performance. XPS, XRD, SEM, high resolution TEM, AC impedance, and other electrochemical methods are applied to resolve the structure–function relationship of the nanostructured Ag@Ag₂S NP electrode

Charge Transport through Electrospun SnO₂ Nanoflowers and Nanofibers: Role of Surface Trap Density on Electron Transport Dynamics

A larger amount of tin precursor was dispersed in electrospun polyvinyl acetate fibers than that required for SnO₂ fiber formation upon annealing, thereby creating a constraint such that all nuclei formed during annealing could not be accommodated within the fiber, which leads to enhanced reaction kinetics and formation of highly crystalline–cum–higher surface area SnO₂ flowers. The flowers are shown to have a lower density of surface trap states than fibers by combining absorption spectra and open circuit voltage decay (OCVD) measurements. Charge transport through the SnO₂ flowers in the presence of the iodide/triiodide electrolyte was studied by OCVD, electrochemical impedance spectroscopy, and transient photodecay techniques. The study shows that the flowers are characterized by higher chemical capacitance, higher recombination resistance, and lower transport resistance compared with fibers. Photocurrent transients were used to extract the effective electron diffusion coefficient and mobility which were an order of magnitude higher for the flowers than that for the fibers. The flowers are also shown to have an enhanced Fermi energy, on account of which as well as higher electron mobility, dye-sensitized solar cells fabricated using the SnO₂ flowers gave <i>V</i>_OC ∼700 mV and one of the highest photoelectric conversion efficiencies achieved using pure SnO₂

NanoCOT: Low-Cost Nanostructured Electrode Containing Carbon, Oxygen, and Titanium for Efficient Oxygen Evolution Reaction

Developing high-efficiency, durable, and low-cost catalysts based on earth-abundant elements for the oxygen evolution reaction (OER) is essential for renewable energy conversion and energy storage devices. In this study, we report a highly active nanostructured electrode, NanoCOT, which contains carbon, oxygen, and titanium, for efficient OER in alkaline solution. The NanoCOT electrode is synthesized from carbon transformation of TiO₂ in an atmosphere of methane, hydrogen, and nitrogen at a high temperature. The NanoCOT exhibits enhanced OER catalytic activity in alkaline solution, providing a current density of 1.33 mA/cm² at an overpotential of 0.42 V. This OER current density of a NanoCOT electrode is about 4 times higher than an oxidized Ir electrode and 15 times higher than a Pt electrode because of its nanostructured high surface area and favorable OER kinetics. The enhanced catalytic activity of NanoCOT is attributed to the presence of a continuous energy band of the titanium oxide electrode with predominantly reduced defect states of Ti (e.g., Ti¹⁺, Ti²⁺, and Ti³⁺) formed by chemical reduction with hydrogen and carbon. The OER performance of NanoCOT can also be further enhanced by decreasing its overpotential by 150 mV at a current density of 1.0 mA/cm² after coating its surface electrophoretically with 2.0 nm IrO_<i>x</i> nanoparticles

Functional Films of Polymer-Nanocomposites by Electrospinning for Advanced Electronics, Clean Energy Conversion, and Storage

An approach for making functional films of polymer – nanocomposites under the framework of nanotechnology is presented. In this methodology, nanowires of an inorganic functional material are dispersed in a functional polymeric medium and the resultant solution is developed into solid films by electrospinning technique. The final structure is a nanofibrous film – each nanofiber contains a percolating network of inorganic nanowires. The nanowires reduce the percolation threshold compared to those nanoparticles and maintain the flexibility and/or light weight of the polymers and nanomaterials. This methodology has been tested for a number of material architectures for electronic and energy devices

Electrochemical and spectroscopic properties of boron dipyrromethene-thiophene-triphenylamine-based dyes for dye-sensitized solar cells

© 2016 American Chemical Society. Because of the current increase in consumption of fossil fuels and its negative impact on the environment, clean energy technologies such as solar cells are highly desirable to address this global energy challenge. Among these, dye-sensitized solar cells (DSSCs) have emerged as potential substitutes to traditional silicon-based solar cells. In this study, a series of boron dipyrromethene (BODIPY)-based dyes (1-5) which contain thiophene and/or triphenylamine (TPA) as redox relays of chromophorebridges are synthesized and characterized using electrochemical and optical spectroscopic methods for their potential applications in DSSCs. Their electrochemical and photophysical properties are investigated and compared with the computational results. DSSCs made of these BODIPY-based dyes exhibit incident photon-to-current conversion efficiencies (IPCE) that correspond to their absorption profiles. BODIPY dye 5 bearing TPA provides the highest power efficiency because of its reversible redox activities, while the dyes bearing thiophene yield a decrease in overall solar cell efficiency because of the irreversible oxidation and electropolymerization of thiophene. Despite their low overall conversion efficiencies, these dyes show interesting structural dependence in their DSSC performance. TiO2 electrodes loaded with these BODIPY dyes are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared analysis to illustrate the surface bonding characteristics of these dyes