Debdutta Ray

Bio: Debdutta Ray is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Pentacene & Charge carrier. The author has an hindex of 4, co-authored 10 publications receiving 37 citations. Previous affiliations of Debdutta Ray include Indian Institutes of Technology.

Spatial Extent of Interaction between Excitons and Polarons in a Bilayer Organic Field-Effect Transistor

Abstract: A major loss mechanism in high intensity organic light-emitting devices is the quenching of excitons in the presence of polarons. In this work, the interaction of excitons in N,N′-di(1-naphthyl)-N,...

Optical polarization anisotropy induced by molecular alignment in pentacene films confined in micron sized grooves etched in SiO2 substrate

Abstract: Pentacene thin films grown on SiO2 substrates with few micron-spaced patterns were found to show anisotropy in their photoluminescence (PL) responses. PL emission was maximum for excitation polarization parallel to the groove direction. Detailed analysis of polarized Raman spectra gave insight on the intermolecular coupling. The anisotropy in PL was found to arise from preferential in-plane molecular alignment of pentacene, induced by the walls of the grooves. This was verified by spatial scan of the polarized micro-PL emission. Though earlier reports have shown anisotropy for nanoscale patterned substrates, to our knowledge, controlled orientation of molecules induced by micron spaced patterning has not been reported so far. This work reports observation of six fold increase in PL response for polarization parallel to the groove of widths 5 μm.

Identification of the nature of excitons in PPDT2FBT using electroabsorption spectroscopy

Abstract: Electroabsorption (EA) measurements can be used to identify the type of excitons contributing to the absorption spectra of semiconductors which have applications in optoelectronics. However, the inferences from the EA measurement greatly depend on the method of fitting and extraction of parameters from the measured spectra. We deconstruct the absorption spectrum by fitting multiple Gaussians and obtain the relative contribution of first and second derivative of each absorption band in EA spectrum, which gives indication of the Frenkel, charge transfer or mixed nature of the excitons involved. We check the applicability of the method for pentacene which is widely used and well studied organic semiconductor. We report EA measurements of poly[(2,5-bis(2-hexyldecyloxy)-phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]-thiadiazole)] (PPDT2FBT). Our analysis shows that besides the feature around 3.07 eV, which is strongly Frenkel-like, most of the absorption bands for PPDT2FBT are mixed states, having relatively high charge transfer contributions. Since charge transfer excitons have higher dissociation efficiencies, we infer PPDT2FBT to be a promising candidate for photovoltaic applications.

Programmable Metal Nanoclusters with Atomic Precision.

Abstract: With the recent establishment of atomically precise nanochemistry, capabilities toward programmable control over the nanoparticle size and structure are being developed. Advances in the synthesis of atomically precise nanoclusters (NCs, 1-3 nm) have been made in recent years, and more importantly, their total structures (core plus ligands) have been mapped out by X-ray crystallography. These ultrasmall Au nanoparticles exhibit strong quantum-confinement effect, manifested in their optical absorption properties. With the advantage of atomic precision, gold-thiolate nanoclusters (Aun (SR)m ) are revealed to contain an inner kernel, Au-S interface (motifs), and surface ligand (-R) shell. Programming the atomic packing into various crystallographic structures of the metal kernel can be achieved, which plays a significant role in determining the optical properties and the energy gap (Eg ) of NCs. When the size increases, a general trend is observed for NCs with fcc or decahedral kernels, whereas those NCs with icosahedral kernels deviate from the general trend by showing comparably smaller Eg . Comparisons are also made to further demonstrate the more decisive role of the kernel structure over surface motifs based on isomeric Au NCs and NC series with evolving kernel or motif structures. Finally, future perspectives are discussed.

Indication of current-injection lasing from an organic semiconductor

Abstract: In this study, we investigate the lasing properties of 4,4'-bis[(N-carbazole)styryl]biphenyl thin films under electrical pumping. The electroluminescent devices incorporate a mixed-order distributed feedback SiO2 grating into an organic light-emitting diode structure and emit blue lasing. The results provide an indication of lasing by direct injection of current into an organic thin film through selection of a high-gain organic semiconductor showing clear separation of the lasing wavelength from significant triplet and polaron absorption and design of a proper feedback structure with low losses at high current densities. This study represents an important advance toward a future organic laser diode technology.