Ashwith Chilvery

Perovskites: transforming photovoltaics, a mini-review

Abstract. The recent power-packed advent of perovskite solar cells is transforming photovoltaics (PV) with their superior efficiencies, ease of fabrication, and cost. This perovskite solar cell further boasts of many unexplored features that can further enhance its PV properties and lead to it being branded as a successful commercial product. This article provides a detailed insight of the organometal halide based perovskite structure, its unique stoichiometric design, and its underlying principles for PV applications. The compatibility of various PV layers and its fabrication methods is also discussed.

Simulation of energy harvesting from roads via pyroelectricity

Power harvesting is the process of extracting useful electrical energy from ambient low grade energy sources such as solar energy, mechanical energy, and thermal energy using smart materials as transducers. These materials have the ability to convert one form of energy into another. This paper aims at thermal-electrical energy converters based on a pyroelectric effect for energy harvesting, and examines its possible use in ultralow power devices and sensor modules. The present work investigates theoretically the energy harvesting capacity of pyroelectric samples fabricated in our laboratory and commercially available pyroelectric elements/transducers by capturing thermal energy of pavements. The single- and polycrystalline elements: triglycine selenate; lithium tantalate; modified lead zirconate titanate; modified lead titanate; modified lead metaniobate; and pyroelectric polymer nanocomposites such as Portland cement; nanocarbon fibers; polymer-lithium tantalate embedded with silver nanoparticles; and others were characterized for applicable performance parameters. The modeling and numerical simulation of energy harvesting capacity of these samples with the available pavements temperature-profile data over an extended period of time were investigated. The results indicate that the electrical energy harvesting via pyroelectricity is a feasible technique for powering autonomous low-duty electric devices.Based on our analysis of a single electric-energy harvesting unit, the triglycine selenate elements shall perform better than others with regard to the amount of voltage and energy densities extracted with respect to time. Possible future work and concepts of developing promising multidomain energy harvesters or hybrid harvesters are also briefly discussed.

Efficient planar perovskite solar cell by spray and brush solution-processing methods

Abstract. Perovskite compounds have the potential to transform photovoltaics technology, as they are easy to fabricate, have better stability, and possess superior power conversion efficiency. In this research, a versatile solution-processing method called “spray+brush” (SB) has been adopted to achieve a power-conversion efficiency of 3.52% for pure organometal halide perovskite devices. It has been observed that this method is more efficient and cost effective than the perovskite devices fabricated by spray (1.95%) and brush (1.17%) methods alone. The SB method of solution processing can be promising for various other organic coatings.

A perspective on the recent progress in solution-processed methods for highly efficient perovskite solar cells

Abstract Perovskite solar cells (PSCs) were developed in 2009 and have led to a number of significant improvements in clean energy technology. The power conversion efficiency (PCE) of PSCs has increased exponentially and currently stands at 22%. PSCs are transforming photovoltaic (PV) technology, outpacing many established PV technologies through their versatility and roll-to-roll manufacturing compatibility. The viability of low-temperature and solution-processed manufacturing has further improved their viability. This article provides a brief overview of the stoichiometry of perovskite materials, the engineering behind various modes of manufacturing by solution processing methods, and recommendations for future research to achieve large-scale manufacturing of high efficiency PSCs.

Characterization of polymeric composite films with MWCNT and Ag nanoparticles

Using a solution casting technique, for sample preparation, pyroelectric multi-walled carbon nanotubes in polyvinylidene fluoride composite films have been fabricated, to allow the characterization of both the pyroelectric and dielectric properties of such composites. The properties measured include: (1) dielectric constants and (2) pyroelectric coefficient as a function of temperature. From the foregoing parameters, figures-of-merit, for infrared detection and thermal-vidicons, were calculated. The results indicated figures-of-merit of composite film were higher than pristine polyvinylidene fluoride films. Additionally, composite films, composed of pyroelectric Lithium tantalate [(LiTaO3), LT] ceramic particles and silver nanoparticles incorporated into polyvinylidene fluoride-trifluoroethylene [PVDF-TrFE) 70/30 mol%] copolymer matrix, have been prepared. The results indicate that silver nanoparticles incorporated lithium tantalate:polyvinylidene fluoride-trifluoroethylene composite films may have application for un-cooled infrared sensor.

Energy harvesting roads via pyroelectric effect: a possible approach

Thermal energy in the environment is a potential and possible source of electric energy for low-power electronics. The ambient temperature variation can be converted into electrical current or voltage via pyroelectric effect. The possibility of the utilizing pyroelectric materials in energy harvesting from roads warrants systematic exploration to take advantage of heat absorbed by the pavements. In terms of voltage generated, the simulated performances, of a few important pyroelectric materials, including fabricated in our laboratory, shall be described by employing real pavement temperature data obtained from climatic database of MEPDG.

Reducing the Bandgap Energy via Doping Process in Lead-Free Thin Film Nanocomposites

There are numerous applications for the pyroelectric composite films in the medical field, military field and environmental applications field. The main focus of this research is to fabricate the higher efficiency thin films that are flexible like the polymers. PVDF is ideal when it comes to making detectors as they are flexible; possess high pyroelectric current and resistance, low dielectric constant and density. Pure PVDF and PVDF films doped with CNT and MWCNT, PVDF: LiTaO3, PVDF: LiTaO3 films doped with MWCNT thin films were fabricated using the solution casting technique. Films fabricated were characterized for their electrical, optical and structural properties using FTIR Spectroscopy, UV-Vis Spectroscopy, and Raman Spectrum. From UV-Vis spectroscopy analysis it is calculated that the indirect bandgap energy of pure PVDF is 5.99 eV, 4.85 eV for PVDF+0.5%-CNT, 4.76 eV for PVDF+1%-CNT, 5.22 eV for PVDF+LT, 4.95 eV for PVDF+LT+2%-MWCNT and 4.85 eV PVDF+LT+2.5%-MWCNT. The calculated direct bandgap energy of pure PVDF is 6.25 eV, 5.95 eV for PVDF+0.5%-CNT, 4.85 eV for PVDF+1%- CNT, 5.42 eV for PVDF+LT, 5.12 eV for PVDF+LT+2%-MWCNT and 4.95 eV PVDF+LT+2.5%-MWCNT. The decrease in the bandgap may be attributed to the presence of unstructured bulk defects. Obtained results show that doping of PVDF and its nanocomposite materials with CNT and MWCNT is enhancing the key characteristics of the materials that are beneficial for the optical devices industry.

Development of nanostructured biocompatible materials for chemical and biological sensors

This research is focused on the fabrication of thin films followed by Surface Enhanced Raman Spectroscopy (SERS) testing of these films for various applications. One technique involves the mixture of nanoparticles with twophoton material to be used as an indicator dye. Another method involved embedding silver nanoparticles in a ceramic nano-membrane. The substrates were characterized by both Atom Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). We applied the nanostructured substrate to measure the SERS spectra of 10^-6 Mol/L Rhodomine 6G(Rh6G), e-coli bacteria and RDX explosive. Our results showed that silver coated ceramic membranes can serve as appropriate substrates to enhance Raman signals. In addition, we demonstrated that the in-house-made colloidal silver can work for enhancement of the Raman spectra for bacteria. We measured the Raman spectra of Rh6G molecules on a substrate absorbed by a nanofluid of silver. We observed several strong Raman bands – 613cm-¹,768 cm^-1,1308cm^-1 1356 cm^-1,1510cm^-1, which correspond to Rh6G vibrational modes υ₅₃,υ6₅,υ1₁₅,υ₁₁₇,υ₁₄₆ respectively, using a ceramic membrane coated by silver. The Raman spectra of Rh6G absorbed by silver nanofluid showed strong enhancement of Raman bands 1175cm^-1 and 1529cm^-1, 1590 cm^-1. Those correspond to vibrational frequency modes – υ₁₀₃,υ₁₅₁,₁₅₂. We also measured the Raman spectra of e-coli bacteria, both absorbed by silver nanofluid, and on nanostructured substrate. In addition, the Fourier Transfer Infrared Spectra (FTIR) of the bacteria was measured.