Satyajit Gupta

Cesium Enhances Long-Term Stability of Lead Bromide Perovskite-Based Solar Cells

Direct comparison between perovskite-structured hybrid organic-inorganic methylammonium lead bromide (MAPbBr3) and all-inorganic cesium lead bromide (CsPbBr3), allows identifying possible fundamental differences in their structural, thermal and electronic characteristics. Both materials possess a similar direct optical band gap, but CsPbBr3 demonstrates a higher thermal stability than MAPbBr3. In order to compare device properties, we fabricated solar cells, with similarly synthesized MAPbBr3 or CsPbBr3, over mesoporous titania scaffolds. Both cell types demonstrated comparable photovoltaic performances under AM1.5 illumination, reaching power conversion efficiencies of ∼6% with a poly aryl amine-based derivative as hole transport material. Further analysis shows that Cs-based devices are as efficient as, and more stable than methylammonium-based ones, after aging (storing the cells for 2 weeks in a dry (relative humidity 15-20%) air atmosphere in the dark) for 2 weeks, under constant illumination (at maximum power), and under electron beam irradiation.

Synthesis and characterization of flexible epoxy nanocomposites reinforced with amine functionalized alumina nanoparticles: a potential encapsulant for organic devices

Research on conducting polymers, organic light emitting diodes and organic solar cells has been an exciting field for the past decade. The challenge with these organic devices is the long term stability of the active material. Organic materials are susceptible to chemical degradation in the presence of oxygen and moisture. The sensitivity of these materials towards oxygen and moisture makes it imperative to protect them by encapsulation. Polymer nanocomposites can be used as encapsulation materials in order to prevent material degradation. In the present work, amine functionalized alumina was used as a cross-linking and reinforcing material for the polymer matrix in order to fabricate the composites to be used for encapsulation of devices. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy were used to elucidate the surface chemistry. Thermogravimetric analysis techniques and CHN analysis were used to quantify grafting density of amine groups over the surface of the nanoparticles. Mechanical characterizations of the composites with various loadings were carried out with dynamic mechanical analyzer. It was observed that the composites have good thermal stability and mechanical flexibility, which are important for an encapsulant. The morphology of the composites was evaluated using scanning electron microscopy and atomic force microscopy.

Encapsulating Bi2Ti2O7 (BTO) with Reduced Graphene Oxide (RGO): An Effective Strategy to Enhance Photocatalytic and Photoelectrocatalytic activity of BTO

Multimetal oxides (AxByOz) offer a higher degree of freedom compared to single metal oxides (AOx) in that these oxides facilitate (i) designing nanomaterials with greater stability, (ii) tuning of the optical bandgap, and (iii) promoting visible light absorption. However, all AxByOz materials such as pyrochlores (A2B2O7)--referred to here as band-gap engineered composite oxide nanomaterials or BECONs--are traditionally prone to severe charge recombination at their surface. To alleviate the charge recombination, an effective strategy is to employ reduced graphene oxide (RGO) as a charge separator. The BECON and the RGO with oppositely charged functional groups attached to them can be integrated at the interface by employing a simple electrostatic self-assembly approach. As a case study, the approach is demonstrated using the Pt-free pyrochlore bismuth titanate (BTO) with RGO, and the application of the composite is investigated for the first time. When tested as a photocatalyst toward hydrogen production, an increase of ∼ 250% using BTO in the presence of RGO was observed. Further, photoelectrochemical measurements indicate an enhancement of ∼ 130% in the photocurrent with RGO inclusion. These two results firmly establish the viability of the electrostatic approach and the inclusion of RGO. The merits of the RGO addition is identified as (i) the RGO-assisted improvement in the separation of the photogenerated charges of BTO, (ii) the enhanced utilization of the charges in a photocatalytic process, and (iii) the maintenance of the BTO/RGO structural integrity after repeated use (established through reusability analysis). The success of the self-assembly strategy presented here lays the foundation for developing other forms of BECONs, belonging to perovskites (ABO3), sillenite (A12BO20), or delafossite (ABO2) groups, hitherto written off due to limited or no photoelectrochemicalactivity.

Hybrid nanocomposite films of polyvinyl alcohol and ZnO as interactive gas barrier layers for electronics device passivation

The development of low cost, easy processable, barrier encapsulant materials is of critical importance for the rapid commercialization of organic/electronic devices. In this study, flexible and thermally stable composites were prepared by simple solution processing using polyvinyl alcohol as the base polymer matrix and reactive zinc oxide nanoparticles as the dispersed phase. These materials were characterized for their applications as barrier materials for moisture and oxygen sensitive organic devices. Various studies such as thermal analysis, mechanical analysis, surface analysis and permeability studies were used to characterize the composite films for their possible use as a passivation material. The material was used to encapsulate Schottky structured devices, and the performance of these encapsulated devices under accelerated weathering was studied.

A Unique Architecture Based on 1 D Semiconductor, Reduced Graphene Oxide, and Chalcogenide with Multifunctional Properties

A unique heterostructured optoelectronic material (HOM), consisting of a reduced graphene oxide (RGO) layer with spatially distributed CdS, suspended by zinc oxide (ZnO) nanorods, is presented. The key features of this HOM are the assembly of the components in a manner so as to realize an effective integration between the constituents and the ability to modify the electronic properties of the RGO. For the first time, the location of RGO (as a suspended layer) along with the tuning of its charge-transport properties (n-/p-type) and its influence on the photo(electro)chemical processes has been examined systematically by using this ZnO/RGO/CdS HOM as a case study. The n-type RGO interlayer facilitates >100 % increase in the photocurrent density and 25 % increase in the photodegradation of a dye, compared to ZnO/CdS, thus demonstrating its multifunctionality. At 3.2 mA cm(-2) , this HOM architecture helps to achieve the highest photocurrent density utilizing ZnO, RGO, and CdS as building blocks in any form. The work is significant for the following reasons: i) other one dimensional (1D) oxides/chalcogenides or 1D oxides/dyes may be designed with similar architectures; ii) HOMs with tunable optical absorbance and charge-transport properties could be realized; iii) related application areas (e.g., sensing or solar fuel generation) should be greatly benefited.

Role of reduced graphene oxide in the critical components of a CdS-sensitized TiO2 -based photoelectrochemical cell.

Nitrogen (N)-doped reduced graphene oxide (nRGO) is systematically incorporated into a TiO(2) -CdS photoelectrochemical (PEC) cell and its role is examined in the three main components of the cell: 1) the CdS-sensitized TiO(2) photoanode, 2) the cathode, and 3) the S(2-)/S(.-) aqueous redox electrolyte. The nRGO layer is sandwiched between TiO(2) nanorods (deposited by using a solvothermal method) and CdS (deposited by using the successive ionic-layer-adsorption and -reaction method). Scanning electron microscopy with energy dispersive X-ray analysis (EDS) reveals the spatial distribution of CdS and nRGO, whereas nRGO formation is evident from Mott Schottky analysis. Chronoamperometry and PEC analysis indicate that upon incorporation of nRGO, a photocurrent density that is at least 27 times higher than that of pristine TiO(2) is achieved; this increase is attributable to the ability of the nRGO to efficiently separate and transport charges. Stability analysis performed by continuous photoillumination over ∼3 h indicates a 26% and 42 % reduction in the photocurrent in the presence and absence of the nRGO respectively. Formation of SO(4)(2-) is identified as the cause for this photocurrent reduction by using X-ray photoelectron spectroscopy. It is also shown that nRGO-coated glass is as effective as a Pt counter electrode in the PEC cell. Unlike the benefits offered by nRGO at the anode and cathode, introducing it in the redox electrolyte is detrimental. Systematic and complementary electrolyte and film-based studies on this aspect reveal evidence of the capacitive behavior of nRGO. Competition between the nRGO and the oxidized electrolyte is identified, based on linear-sweep voltammetry analysis, as the limiting step to efficient charge transport in the electrolyte.

Synthesis and characterization of silicone polymer/functionalized mesostructured silica composites

A thermally stable and flexible composite has been synthesized by following a consecutive ‘two–step’, solvent free route. Silicone polymer containing internal hydrides was used as a polymer matrix and mesoporous silica functionalized with allytrimethoxysiloxane was used as a filler material. In the second step, the composite preparation was carried out using the hydrosilylation reaction mediated by ‘Karastedt’ platinum catalyst. The results of the studies suggest that the composites are thermally stable, hydrophobic and flexible and can be potentially used for encapsulating flexible electronic devices.

A one-pot strategy for coupling chalcogenide nanocrystals with 1D oxides for solar-driven processes

This work presents a simple approach to the synthesis of CdS coatings on TiO2 nanotubes (T_NTs) and to form a heterostructured composite. A non-pressure based, single precursor one-pot approach performed at a temperature of 160 °C is used to assemble CdS on the TiO2 surface. Surface characterization using microscopy, X-ray diffraction, and elemental analysis indicates the formation of dense hexagonal 〈002〉 CdS nanocrystals along the nanotube walls and inter-tubular spacing. Optical measurements indicate that the CdS absorbs in the visible region and demonstrates a red shift with increased loading: up to 12 nm red shift is noted when the precursor concentration is increased from 0.1–3 mM. The 0D CdS/1D T_NT was also tested as an anode in a photoelectrochemical cell. The electrode produced the highest reported photocurrent of 9.3 mA cm−2 under UV-visible illumination when compared with similar systems. The method may be used in assembling efficient photoanodes for multifunctional solar-driven processes.

Future Scope of Silicone Polymer based Functionalized Nanocomposites forDevice Packaging: A Mini Review

Organic electronic devices, such as conducting polymer and/or perovskite based solar cells are highly promising and emerging, but they are highly unstable in the presence of moisture and oxygen. It is important to protect these devices from these deterrent gases by using a suitable encapsulant and to improve the lifetime of these promising devices. “Silicone polymer” impregnated with suitable functionalized nano fillers/moisture or oxygen scavengers can be potentially used for sensitive organic device encapsulation applications, where a combined property of flexibility, thermal stability, transparency, and low moisture permeation is critical. Suitable fillers can also enhance the thermomechanical properties of silicone polymers, which is also important for hermitic sealing applications. Silicone polymer have a wide range of applications in electronic, mechanical, and biological industries, due to their flexibility over a broad temperature window, resiliency, transparency, superior thermal stability, resistant to aging and degradation from sunlight. This polymer also coats a surface conformally, having moisture resistance property and inertness. In this minireview, functionalized composites based on silicone polymers, which have been developed for the potential organic device encapsulation application, has been discussed. In addition to that, future direction towards the fabrication of new functionalized nanocomposites, based on silicone polymers is also discussed briefly.