Browsing by Author "Rajiv Kumar Pandey"

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Evolution of Edge-On Oriented Polymer Films Self-Assembled at the Air-Liquid Interface for High-Performance Electronic Device Applications
(American Chemical Society, 2022) Subhajit Jana; Rajiv Kumar Pandey; Rajiv Prakash
In the context of semicrystal growth in thin films of organic semiconducting polymers (OSPs) at the air-liquid interface, polymer self-assembly is mainly governed by convective Marangoni flow, compressive viscous force, divergent evaporation flux, and high conformational degrees of freedom of OSPs, which lead to a very complex microstructure having many cumulative and noncumulative disorders. In this regard, first time, major polythiophene derivatives such as poly(3-hexylthiophene-2,5-diyl) (P3HT), poly(3,3‴-didodecyl[2,2′:5′,2″:5′′,2′′′-quaterthiophene]-5,5′′′-diyl) (PQT), and poly[2,5-bis (3- tetradecylthiophen-2-yl) thieno[3,2-b]thiophene] (PBTTT) are collectively employed as model OSPs to explain film growth on aqueous substrates and examined using multiple characterization techniques. At first, we have investigated the degree of paracrystalline disorder along (h00) direction in three different polymer backbone structures. Then, the local in-plane orientation of the polymer chains in crystalline domains along the π-πstacking direction has been studied using the bright field HR-TEM images. Moreover, quantum mechanical penetration of localized trap states into the bandgap induced by those structural imperfections has also been quantified from optical property measurements. Finally, we have studied the charge transport properties in all three directions (out-of-plane and in-plane viz. along and across the polymer chains) of the thin solid polymeric films using vertical and planar device architectures. We have observed maximum out-of-plane mobility (μh) 3.7 × 10-5cm2/V·s for P3HT, and in-plane mobility, μh(along the polymer chains) 0.234 cm2/V·s for PBTTT. By considering the obtained results from different characterizations and all possible flow processes, we have tried to propose the exact growth mechanism of these thin films. Thus, our findings give an insight into the fundamentals of polymer self-assembly to a structure-property correlation, which is extremely important for material processing and device engineering to meet the growing technological appeal. © 2022 American Chemical Society.
Surface driven nano-morphology of poly 3-hexylthiophene film, and their photophysical, spectral and electronic traits
(Elsevier Ltd, 2020) Rajiv Kumar Pandey; Hemlata Bisht; Swatantra K. Yadav; Arun Kumar Singh; Rajiv Prakash; Hirdyesh Mishra
The present paper compiles, the substrate driven nano-morphology of fluorescent semiconducting poly 3-hexylthiophene (P3HT) polymer films and their effects on photophysical, spectral, and electronic behaviour. Surface morphological study reveals regular long sized aggregation and large crystalline structure of polymer thin film in liquid surface grown (LSG) film as compared to hard surface grown (HSG) film. Experimentally observed and computationally simulated Raman spectra show that HJ coupling dominates in LSG film compared to HSG film. LSG film yields the structured electronic absorption and emission spectra with increased radiative decay time, in comparison to HSG film. These indicate a decrease of non-radiative transitions in LSG film and support more crystalline nature of the P3HT film as well as improve intrinsic mobility and device parameters in the sandwiched structure of Schottky diode configuration. The findings show that LSG based electronic/photonic devices have a high potential for enhanced performance at a little cost. © 2020