Shweta Agarwala

Perovskite Solar Cells: Beyond Methylammonium Lead Iodide

Organic-inorganic lead halide based perovskites solar cells are by far the highest efficiency solution-processed solar cells, threatening to challenge thin film and polycrystalline silicon ones. Despite the intense research in this area, concerns surrounding the long-term stability as well as the toxicity of lead in the archetypal perovskite, CH3NH3PbI3, have the potential to derail commercialization. Although the search for Pb-free perovskites have naturally shifted to other transition metal cations and formulations that replace the organic moiety, efficiencies with these substitutions are still substantially lower than those of the Pb-perovskite. The perovskite family offers rich multitudes of crystal structures and substituents with the potential to uncover new and exciting photophysical phenomena that hold the promise of higher solar cell efficiencies. In addressing materials beyond CH3NH3PbI3, this Perspective will discuss a broad palette of elemental substitutions, solid solutions, and multidimensional families that will provide the next fillip toward market viability of the perovskite solar cells.

A maskless synthesis of TiO2-nanofiber-based hierarchical structures for solid-state dye-sensitized solar cells with improved performance.

TiO2 hierarchical nanostructures with secondary growth have been successfully synthesized on electrospun nanofibers via surfactant-free hydrothermal route. The effect of hydrothermal reaction time on the secondary nanostructures has been studied. The synthesized nanostructures comprise electrospun nanofibers which are polycrystalline with anatase phase and have single crystalline, rutile TiO2 nanorod-like structures growing on them. These secondary nanostructures have a preferential growth direction [110]. UV–vis spectroscopy measurements point to better dye loading capability and incident photon to current conversion efficiency spectra show enhanced light harvesting of the synthesized hierarchical structures. Concomitantly, the dye molecules act as spacers between the conduction band electrons of TiO2 and holes in the hole transporting medium, i.e., spiro-OMeTAD and thus enhance open circuit voltage. The charge transport and recombination effects are characterized by electrochemical impedance spectroscopy measurements. As a result of improved light harvesting, dye loading, and reduced recombination losses, the hierarchical nanofibers yield 2.14% electrochemical conversion efficiency which is 50% higher than the efficiency obtained by plain nanofibers.

Fabrication of titanium based biphasic scaffold using selective laser melting and collagen immersion

Tissue engineering approaches have been adopted to address challenges in osteochondral tissue regeneration. Single phase scaffolds, which consist of only one single material throughout the whole structure, have been used extensively in these tissue engineering approaches. However, a single phase scaffold is insufficient in providing all the properties required for regeneration and repair of osteochondral defects. Biphasic scaffolds with two distinct phases of titanium/type 1 c ollagen and titanium-tantalum/type 1 collagen were developed for the first time using selective laser melting and collagen infiltration. Observation of the biphasic scaffolds demonstrated continuous interface between the two phases and mechanical characterization of the metallic scaffolds support the feasibility of the newly developed scaffolds for tissue engineering in osteochondral defects.

Novel method for the fabrication of ultrathin, free-standing and porous polymer membranes for retinal tissue engineering

Retinal degeneration causes permanent visual loss and affects millions of people worldwide. Cell transplantation may have the potential for retinal regeneration. However, several problems hinder the successful repair of the retina including cell delivery, integration, and survival. Recent studies have shown that the use of scaffolds can address these obstacles. Synthetic scaffolds are being explored to mimic the functions of Bruchs membrane, an extracellular matrix that acts as a molecular sieve, to maintain the metabolic exchange between the vasculature and outer retina. This work aims at fabricating an ultrathin and porous membrane, which mimics Bruchs membrane, using a novel method. We have developed a fast, easy and single-step method to create a free-standing, porous and ultrathin PCL membrane, through dropcasting of a polymer blend on a liquid interface. The free-standing scaffold with nanometer pores is investigated for human retinal pigment epithelial (RPE) cell response. The results demonstrate that the synthesised membrane can act as a potential prosthetic Bruchs membrane for RPE transplantation.

Optimizing aerosol jet printing process of silver ink for printed electronics

Aerosol jet is an additive manufacturing technique that writes electronic inks directly onto the surface. The process has great potential for printed electronics as it is non-contact method that works well with variety of materials- metals, insulators, semiconductors, epoxy and encapsulation materials for conformal writing. This paper explores the effect of some parameters like ultrasonic power and atomizer flow on overall print quality, thus establishing a process window.

Aerosol jet printed pH sensor based on carbon nanotubes for flexible electronics

The monitoring of pH is valuable for many environmental, industrial, and biological applications. Here, we develop a flexible pH sensor using CNT material using aerosol jet technology. The chemiresistive pH sensor is fabricated with a CNT-based miniaturized serpentine sensing element printed on top of the silver electrodes. Aerosol jet printing parameters are optimized to achieve high resolution printing. The fabricated pH sensor shows good sensitivity and repeatability.

High resolution aerosol jet printing of conductive ink for stretchable electronics

Stretchable electronics is gaining wide spread attention due to its application in many applications such as wearable devices, soft robotics, biomedical and consumer products. Aerosol jet printing, which is capable of printing very fine features, can be used to fabricate high performance flexible electronic devices. In this paper, we explore aerosol jet process technique to print conductive stretchable ink for fabricating new-age electronic circuits. Functional composite ink made of silicone and silver composite were used to print directly on stretchable silicone rubber substrate. Electronic functional devices such as flexible circuit and strain gauge were successfully printed, characterized and tested for stretchability.