Pawan K. Kanaujia

In Situ Intercalation Dynamics in Inorganic–Organic Layered Perovskite Thin Films

The properties of layered inorganic semiconductors can be manipulated by the insertion of foreign molecular species via a process known as intercalation. In the present study, we investigate the phenomenon of organic moiety (R-NH3I) intercalation in layered metal-halide (PbI2)-based inorganic semiconductors, leading to the formation of inorganic–organic (IO) perovskites [(R-NH3)2PbI4]. During this intercalation strong resonant exciton optical transitions are created, enabling study of the dynamics of this process. Simultaneous in situ photoluminescence (PL) and transmission measurements are used to track the structural and exciton evolution. On the basis of the experimental observations, a model is proposed which explains the process of IO perovskite formation during intercalation of the organic moiety through the inorganic semiconductor layers. The interplay between precursor film thickness and organic solution concentration/solvent highlights the role of van der Waals interactions between the layers, as well as the need for maintaining stoichiometry during intercalation. Nucleation and growth occurring during intercalation matches a Johnson–Mehl–Avrami–Kolmogorov model, with results fitting both ideal and nonideal cases.

Strong Photocurrent from Two-Dimensional Excitons in Solution-Processed Stacked Perovskite Semiconductor Sheets.

Room-temperature photocurrent measurements in two-dimensional (2D) inorganic–organic perovskite devices reveal that excitons strongly contribute to the photocurrents despite possessing binding energies over 10 times larger than the thermal energies. The p-type (C6H9C2H4NH3)2PbI4 liberates photocarriers at metallic Schottky aluminum contacts, but incorporating electron- and hole-transport layers enhances the extracted photocurrents by 100-fold. A further 10-fold gain is found when TiO2 nanoparticles are directly integrated into the perovskite layers, although the 2D exciton semiconducting layers are not significantly disrupted. These results show that strong excitonic materials may be useful as photovoltaic materials despite high exciton binding energies and suggest mechanisms to better understand the photovoltaic properties of the related three-dimensional perovskites.

Direct deposition strategy for highly ordered inorganic organic perovskite thin films and their optoelectronic applications

A direct deposition methodology has been optimized for highly crystalline inorganic-organic (IO) perovskite thin films. The simplest deposition ensures long-range order with high c-oriented thin films, thicknesses ranging from ultra-thin (~20nm) and upto 1.5 µm. These self-assembled layered perovskites are naturally aligned alternative stacking arrangement of inorganic and organic monolayers, resemble multiple quantum wells (MQWs), which offers superior optoelectronic properties such as room-temperature optical excitons, strong electrically induced photo-carrier mobilities etc. The established fabrication is having device-compatible advantage over other conventional solution–processed thin films wherein the optical features are restricted by thickness limitations (<200nm) and with possible corrugated surface morphologies with multi-phases. The universally acceptable ability has been demonstrated for wide varieties of organic moieties (R) as well as different lead halide networks in type (R-NH3)2PbX4 (X = I, Br,Cl).The potential of the direct deposition methodology for demonstrated in 3D template structure fabrication as well as in photocurrent response capability.

Effect of volatile solvent infiltration on optical and electrical characteristics of porous photonic structures

The infiltration of small chain alcohols into the deep nano sized pores of one dimensional porous silicon (PS) based photonic structures have been continuously monitored against time by simultaneous electrical and optical measurements. The in situ optical reflection studies during volatile solvent exposure reveal several dynamic processes; within a limited time duration of solvent exposure the microcavity resonant peak shifts towards higher wavelength, and after prolonged exposure and drying the cavity resonant peak shifts to a new semi-permanent lower wavelength. In situ optical and electrical responses from PS photonic structure-based low-cost multifunctional devices reveal their potential application for a wide range of chemical and biological species detection and monitor their sensor dynamic processes.

Magnetic phase transition in layered inorganic-organic hybrid (C12H25NH3)2CuCl4

Inorganic-organic (IO) hybrids are material systems which have become an interesting theme of research for physicist and chemists recently due to the possibility of engineering specific magnetic, thermal or optoelectronic properties by playing around with the transition metal, halides and the organic components. Our experiments on (C12H25NH3)2CuCl4 show that the system exhibits a long range ferromagnetic order below ∼11 K. In such an inorganic-organic hybrid system, Jahn-Teller distortion of the copper ions results into a weak ferromagnetic order as compared to the antiferromagnetic spin-spin exchange in the pure inorganic CuCl2 compound. Moreover, this particular hybrid system also exhibits photoluminescence when excited below absorption maximum related to charge transfer peak though the effect is much weaker as compared to that in extensively studied other MX4-based (M = Sn, Pb; X = Cl, Br, I) counterparts.Inorganic-organic (IO) hybrids are material systems which have become an interesting theme of research for physicist and chemists recently due to the possibility of engineering specific magnetic, thermal or optoelectronic properties by playing around with the transition metal, halides and the organic components. Our experiments on (C12H25NH3)2CuCl4 show that the system exhibits a long range ferromagnetic order below ∼11 K. In such an inorganic-organic hybrid system, Jahn-Teller distortion of the copper ions results into a weak ferromagnetic order as compared to the antiferromagnetic spin-spin exchange in the pure inorganic CuCl2 compound. Moreover, this particular hybrid system also exhibits photoluminescence when excited below absorption maximum related to charge transfer peak though the effect is much weaker as compared to that in extensively studied other MX4-based (M = Sn, Pb; X = Cl, Br, I) counterparts.

Investigating resonance energy transfer from protein molecules to van der Waals nanosheets

The resonance energy transfer (RET) from tryptophan present in bovine serum albumin (BSA) to two dimensional (2D) nanomaterials has been reported. In these bio-nano systems, BSA molecules act as efficient donors while 2D van der Waals nanosheets of graphene, molybdenum disulfide (MoS2) and tungsten disulfide (WS2) act as acceptors. The fluorescence emission from tryptophan arises at 350 nm, in presence of 2D nanosheets, the fluorescence intensity of BSA decreases. The time resolved fluorescence study shows that there is decrease in the fluorescence lifetime of BSA molecules in presence of 2D nanosheets. The decrease in fluorescence lifetime of BSA confirms the energy transfer phenomenon in bio-nano interactions.

Alkaline earth coordination polymers: photoluminescence and dielectric properties

There is considerable interest in seeking new dielectric materials due to their potential applications in modern electronic devices such as memory elements, high performance insulators and resonators.1 Search for new dielectric materials still poses formidable challenge owing to stringent permittivity requirements imposed by operative frequency, power levels, types of application and stability.2 Recently, CPs/MOFs are being sought as low dielectric constant (low-κ) materials for interlayer dielectrics with high thermal stability, electrically insulating property.3 Alkaline-earth metal coordination polymers are promising candidates for exploring dielectric and ferroelectric properties. Since the framework lacks positional freedom, dielectric constants of these solids are expected to be very low and mostly arise from mobile solvent molecules and polarizability of the organic linkers. In this work, we attempted to explore the structural landscape of calcium or strontium based dicarboxylates under solvothermal condition with an objective was to study the influence of selected aromatic dicarboxylic acid based ligands and polar aprotic solvents in dictating the crystal structures of the final solids. In this poster, we report crystal structure, photoluminescence and dielectric properties of several new alkaline-earth CPs.