Tejendra Dixit

Influence of potassium permanganate on the anisotropic growth and enhanced UV emission of ZnO nanostructures using hydrothermal process for optoelectronic applications

The effect of in situ addition of potassium permanganate (KMnO4) in controlling morphology, composition, structural and optical properties of the ZnO nanostructures prepared by hydrothermal technique has been investigated. The influence of synthesis conditions on the growth of ZnO nanorods was meticulously studied by field-emission scanning electron microscope, X-ray diffractometer, transmission electron microscopy (TEM) and high-resolution TEM. It is demonstrated that the KMnO4 concentration has great influence on the morphology and on the alignment of ZnO nanorods. Further the optical properties of nanostructures were investigated by photoluminescence (PL) spectroscopy and ultraviolet–visible diffuse reflectance spectroscopy. The PL spectrum divulged a continuous suppression of defect-related broadband emission by increasing the concentration of the KMnO4, which produced the quenching of surface defects present in the nanorods. The intensity ratio of the peaks corresponding to near-band emission (NBE) to that of deep-level emission of the KMnO4-modified ZnO nanorods was found to increase by eightfold of magnitude. Further it must be noted that nearly 17-fold enhancement in the PL emission of the peak corresponding to NBE was observed in KMnO4-modified ZnO compared to the ZnO grown without any additive. The I–V plot showed dependence of current values under dark and illumination over the amount of KMnO4 added during the growth stage.Graphical Abstract

Improved Photoresponse of Hybrid ZnO/P3HT Bilayered Photodetector Obtained Through Oriented Growth of ZnO Nanorod Arrays and the Use of Hole Injection Layer

We report highly oriented one-dimensional (1-D) growth of zinc oxide (ZnO) nanorod arrays (NRA) which were later utilized to fabricate hybrid photodiodes having the typical photodiode configuration of indium tin oxide (ITO)/ZnO/poly(3-hexylthiophene) (P3HT)/Ag. These functional hybrid bilayered photodiodes were found to have high rectification ratio under dark conditions and demonstrated enhanced responsivity under light illumination. Further, we studied the effect of an intermediate electron blocking layer of poly(ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) on the photodiode characteristics and demonstrated ITO/ZnO/P3HT/PEDOT:PSS/Ag photodiodes, reporting very high rectification ratio and responsivity in this bilayered configuration. The observed results are explained on the basis of the increased surface area of contact between the ZnO nanorods and the P3HT, and also the efficient hole injection into the P3HT layer from the top Ag electrode.

Insights into non-noble metal based nanophotonics: exploration of Cr-coated ZnO nanorods for optoelectronic applications

Herein, the room temperature photoluminescence and Raman spectra of hydrothermally grown ZnO nanorods coated with Cr are investigated for optoelectronic applications. A thorough examination of the photoluminescence spectra of Cr coated ZnO nanorods showed the suppression of deep level emissions by more than twenty five times with Cr coating compared to that of pristine ZnO nanorods. Moreover, the underlying mechanism was proposed and can be attributed to the formation of Schottky contacts between Cr and ZnO resulting in defect passivation, weak exciton–plasmon coupling, enhanced electric field effect and formation of hot carriers due to interband transitions. Interestingly, with the increase in sputtering time, the ratio of the intensities corresponding to the band gap emission and deep level emission was observed to increase from 6.2 to 42.7, suggesting its application for UV only emission. Further, a planar photodetector was fabricated (Ag–ZnO–Ag planar configuration) and it was observed that the dark current value got reduced by more than ten times with Cr coating, thereby opening up its potential for transistor applications. Finally, Cr coated ZnO nanorods were employed for green light sensing. Our results demonstrated that ZnO nanorods decorated with Cr shed light on developing stable and high-efficiency non-noble metal based nanoplasmonic devices such as photodetectors, phototransistors and solar cells.

Improved photo response of hybrid ZnO/P3HT bilayered photo diode

In this work we present the fabrication & characterization of hybrid bilayer photodiode based on aligned zinc oxide (ZnO) nanorods and poly(3-hexylthiophene) (P3HT). These functional hybrid bi-layered photodiodes showed excellent diode characteristics & were found to have a high rectification ratio under dark conditions & demonstrated enhanced responsivity under illumination. It was observed that highly anisotropic growth of ZnO occurred with the addition of KMnO4 resulting in oriented growth of ZnO nanorod arrays. Further the effect of in situ addition of KMnO4 on ZnO/P3HT photodiode. Further we studied the effect of ZnO grown for various KMnO4 concentrations on ZnO/P3HT photodiode. The results indicate that the increased surface area of contact between the ZnO nanorods & the P3HT, & reduction in defect states of ZnO led to the better responsivity of photodiode.