Ramakant Sharma

An enhanced electrochemical and cycling properties of novel boronic Ionic liquid based ternary gel polymer electrolytes for rechargeable Li/LiCoO 2 cells

A new generation of boronic ionic liquid namely 1-ethyl-3-methylimidazolium difluoro(oxalate)borate (EMImDFOB) was synthesized by metathesis reaction between 1-ethyl-3-methylimiazolium bromide and lithium difluoro(oxalate)borate (LiDFOB). Ternary gel polymer electrolyte membranes were prepared using electrolyte mixture EMImDFOB/LiDFOB with poly vinylidenefluoride-co-hexafluoropropylene (PVdF-co-HFP) as a host matrix by facile solvent-casting method and plausibly demonstrated its feasibility to use in lithium ion batteries. Amongst ternary gel electrolyte membrane, DFOB-GPE3, which contained 80 wt% of EMImDFOB/LiDFOB and 20 wt% PVdF-co-HFP, showed excellent electrochemical and cycling behaviors. The highest ionic conductivity was found to be 10−3 Scm−1 at 378 K. Charge-discharge profile of Li/DFOB-GPE3/LiCoO2 coin cell displayed a maximum discharge capacity of 148.4 mAhg−1 at C/10 rate with impressive capacity retention capability and columbic efficiency at 298 K.

Dual role of boron in improving electrical performance and device stability of low temperature solution processed ZnO thin film transistors

In this paper, we have demonstrated the dual role of boron doping in enhancing the device performance parameters as well as the device stability in low temperatures (200 °C) sol-gel processed ZnO thin film transistors (TFTs). Our studies suggest that boron is able to act as a carrier generator and oxygen vacancy suppressor simultaneously. Boron-doped ZnO TFTs with 8 mol. % of boron concentration demonstrated field-effect mobility value of 1.2 cm2 V−1 s−1 and threshold voltage of 6.2 V, respectively. Further, these devices showed lower shift in threshold voltage during the hysteresis and bias stress measurements as compared to undoped ZnO TFTs.

GaAs metal-oxide-semiconductor based nonvolatile memory devices embedded with ZnO quantum dots

Ultrathin InP passivated GaAs non-volatile memory devices were fabricated with chemically synthesized 5 nm ZnO quantum dots embedded into ZrO2 high-k oxide matrix deposited through metal organic chemical vapor deposition. In these memory devices, the memory window was found to be 6.10 V and the obtained charge loss was only 15.20% after 105 s. The superior retention characteristics and a wide memory window are achieved due to presence of ZnO quantum dots between tunneling and control oxide layers. Room temperature Coulomb blockade effect was found in these devices and it was ascertained to be the main reason for low leakage. Electronic band diagram with program and erase operations were described on the basis of electrical characterizations.

Interface engineering through electron transport layer modification for high efficiency organic solar cells

In the present study, we have compared the device performance of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thio-phene-)-2-carb-oxylate-2-6-diyl)] (PTB7-Th):phenyl-C71-butyric acid methyl ester (PCBM) organic solar cells (OSCs) in an inverted geometry with ZnO, a bilayer of ZnO and Ba(OH)2 [ZnO/Ba(OH)2] and a nanocomposite of ZnO and Ba(OH)2 [ZnO:Ba(OH)2] as electron transport layers (ETLs). Our study reveals that the performance of the devices with the ZnO/Ba(OH)2 and ZnO:Ba(OH)2 nanocomposite as ETL supersedes that of devices with only ZnO as ETL. The plausible reasons for the improved performance of these devices are identified using morphological studies, contact angle measurements, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and photo-electrochemical impedance spectroscopy (EIS) measurements. It is observed that films of ZnO/Ba(OH)2 and ZnO:Ba(OH)2 nanocomposites have a low work function and are slightly more smooth and hydrophobic than ZnO films. This might have suppressed the charge recombination and thereby improved the charge collection as has been confirmed by EIS measurements.

Enhanced efficiency of inverted bulk heterojunction solar cells with embedded silica nanoparticles

Incorporation of nanoparticles in the active layer is one of the possible approaches to improve the efficiency of bulk heterojunction organic solar cells (BHJ OSCs). Here, we have synthesized silica nanoparticles (SiO2 NPs) using the modified stober method and studied the dispersion of various concentrations of SiO2 NPs in poly (3-hexylthiophene), [6, 6]-phenyl C61-butyric acid methyl ester (P3HT: PCBM) blend. It was found that the inverted geometry device with concentration of 2 wt% of SiO2 NPs and having the structure ITO/ZnO (NPs)/P3HT: PCBM: SiO2 NPs/MoO3/Al shows a maximum efficiency of 1.95 %, which is more than 32 % larger compared to devices without SiO2 NPs. UV-Vis absorption measurements suggest that the incorporation of SiO2 NPs into a P3HT: PCBM blend improves the absorption. This absorption enhancement, supported also by finite difference time domain (FDTD) calculations of Mie scattering, results in the observed efficiency improvement.

Thermal annealing study on P3HT: PCBM based bulk heterojunction organic solar cells using impedance spectroscopy

Recently, Thermal annealing is an important process for bulk heterojunction organic solar cells (BHJ OSCs) to improve the device efficiency and performance of the organic solar cells. Here in, we have examined the changes in the efficiency and morphology of P3HT: PCBM film according to the thermal annealing temperature to find the changes during the annealing process by measuring the optical absorption, atomic force microscope and X-ray diffraction. We also investigated the effect of different annealing process conditions (without, pre- and post-annealing) on the device performance of the inverted bulk heterojunction organic solar cells consist the structure of ITO/ ZnO / P3HT: PCBM / MoO3/ Al by measuring AC impedance characteristics. Particularly, the power conversion efficiency (PCE), crystalline nature of the polymer, light absorption and the surface smoothness of P3HT: PCBM films are significantly improved after the annealing process. These results indicated the improvement in terms of PCE, interface...