Narayan K. S.

Cu Doping in Ligand Free CdS Nanocrystals: Conductivity and Electronic Structure Study

2017-02-21T10:24:58Z

Cu Doping in Ligand Free CdS Nanocrystals: Conductivity and Electronic Structure Study Grandhi, G. Krishnamurthy; Swathi, K.; Narayan, K. S.; Viswanatha, Ranjani Ligand-free Cu-doped CdS nanocrystals (NCs) have been synthesized to elucidate their surface electronic structure. The Cu-doped ligand-free NCs unlike their undoped counterparts are shown to be luminescent. We used this Cu-related emission as a probe to study the nature of the surface trap states that results in negligible luminescence in the undoped NCs. The concentration of the sulfide ligands is shown to play a crucial role in the surface passivation of the NCs. Electrical conductivity of these NCs was also studied, and they were shown to exhibit significant conductivity of similar to 10(-4) S cm(-1). Further we have shown that the electrical conductivity is closely correlated to the surface charge and hence the trap states of the individual NCs have far-reaching consequences in the device optimization. Restricted Access

Morphology and electrostatics play active role in neuronal differentiation processes on flexible conducting substrates

2017-02-21T10:24:25Z

Morphology and electrostatics play active role in neuronal differentiation processes on flexible conducting substrates Srivastava, Nishit; James, Jackson; Narayan, K. S. This commentary discusses and summarizes the key highlights of our recently reported work entitled "Neuronal Differentiation of Embryonic Stem Cell Derived Neuronal Progenitors Can Be Regulated by Stretchable Conducting Polymers." The prospect of controlling the mechanical-rigidity and the surface conductance properties offers a unique combination for tailoring the growth and differentiation of neuronal cells. We emphasize the utility of transparent elastomeric substrates with coatings of electrically conducting polymer to realize the desired substrate-characteristics for cellular development processes. Our study showed that neuronal differentiation from ES cells is highly influenced by the specific substrates on which they are growing. Thus, our results provide a better strategy for regulated neuronal differentiation by using such functional conducting surfaces. Restricted Access

Organic photovoltaics: key photophysical, device and design aspects

2017-02-21T10:24:24Z

Organic photovoltaics: key photophysical, device and design aspects Joshi, Dhruv; Shivanna, Ravichandran; Narayan, K. S. Key aspects of Organic Photovoltaics (OPVs) have been reviewed in this tutorial. Issues pertaining to the choice of materials, fabrication processes, photophysical mechanisms, device characterization, morphology of active layers and manufacturing are discussed. Special emphasis has been given to recent developments in large-area modules. Current strategies in enhancing the performance using external optical engineering approaches have also been highlighted. OPVs as a technology combine low weight, flexibility, low cost, good form factor and high-throughput processing; making them a promising PV technology for the future. Restricted Access

Nanostructured Donor-Acceptor Self Assembly with Improved Photoconductivity

2017-02-21T10:24:36Z

Nanostructured Donor-Acceptor Self Assembly with Improved Photoconductivity Saibal, B.; Ashar, A. Z.; Devi, R. Nandini; Narayan, K. S.; Asha, S. K. Nanostructured supramolecular donor-acceptor assemblies were formed when an unsymmetrical N-substituted pyridine functionalized perylenebisimide (UPBI-Py) was complexed with oligo(p-phenylenevinylene) (OPVM-OH) complementarily functionalized with hydroxyl unit and polymerizable methacrylamide unit at the two termini. The resulting supramolecular complex [UPBI-Py (OPVM-OH)](1.0) upon polymerization by irradiation in the presence of photoinitiator formed well-defined supramolecular polymeric nanostructures. Self-assembly studies using fluorescence emission from thin film samples showed that subtle structural changes occurred on the OPV donor moiety following polymerization. The 1:1 supramolecular complex showed red-shifted aggregate emission from both OPV (similar to 500 nm) and PBI (similar to 640 nm) units, whereas the OPV aggregate emission was replaced by intense monomeric emission (similar to 430 nrn) upon polymerizing the methacrylamide units on the OPVM-OH. The bulk structure was studied using wide-angle X-ray diffraction (WXRD). Complex formation resulted in distinct changes in the cell parameters of OPVM-OH. In contrast, a physical mixture of 1 mol each of OPVM-OH and UPBI-Py prepared by mixing the powdered solid samples together showed only a combination of reflections from both parent molecules. Thin film morphology of the 1:1 molecular complex as well as the supramolecular polymer complex showed uniform lamellar structures in the domain range <10 rim. The donor-acceptor supramolecular complex [UPBI-Py (OPVM-OH)](1.0) exhibited space charge limited current (SCLC) with a bulk mobility estimate of an order of magnitude higher accompanied by a higher photoconductivity yield compared to the pristine UPBI-Py. This is a very versatile method to obtain spatially defined organization of n and p-type semiconductor materials based on suitably functionalized donor and acceptor molecules resulting in improved photocurrent response using self-assembly. Restricted Access