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Organic and Nanostructured Electronics Lab Vladimir Bulović Mission Facili.es and Unique Approaches We are large-area nanotechnologists developing practical devices and structures from physical insights discovered at the nanoscale. Our work demonstrates that nanoscale materials such as molecules, polymers, and nanocrystal quantum dots can be assembled into large area functional optoelectronic devices that surpass the performance of today's state-of-the-art. We combine insights into physical processes within nanostructured devices, with advances in thin film processing of nanostructured material sets, to launch new technologies and glimpse into the polaron and exciton dynamics that govern the nanoscale. The ONE Lab supports over 60 users with various micro- and nano-fabrication and characterization instruments and equipment, including solar cell testing systems, thermal evaporation and sputtering chambers for deposition of organics, metals, and oxides, and optical lab space with wavelength-tunable, high power sub-picosecond laser. The research group consists of members of diverse research interests and experiences, creating a conducive environment for collaborative work. Photonic Materials, Devices, and Systems Nanoscale Science and Engineering Quantum Dot Light EmiJng Diodes (QDLEDs) The stable, highly saturated emission and tunable bandgap of solution-processed colloidal quantum dots (QDs) make them useful for light-emitting devices. Energy, Power and Electronics Quantum Dot Photovoltaic (QDPVs) With band-gaps tunable from 0.5 to 2.1 eV, PbS and PbSe QDs offer infrared spectral responsivity surpassing that of organic materials, making these QDs promising for use as absorptive layers in PVs. Field Driven Electroluminescence The dynamics of charge transport within the QD layer are studied using electrical and spectroscopic measurements to determine the main limitations of device performance in QDLEDs. Ligand Exchange in PbS QDs QD surfaces are passivated with organic ligands. By tuning the ligand length and functionality we can optimize the transport properties and interfacial energetics of QD solids. ZnO Nanowire QDPVs ZnO nanowire transport layer decouples absorption from collection, extending the effective depletion width throughout a thick QD film. Progress is rapid and promising: Engineering energy barriers Op4mal mul4junc4on subcell bandgaps: Metal oxide transport layers are used to remove barriers to electron extraction. Brown, P.R. et al, “Improved current extrac4on from ZnO/PbS quantum dot heterojunc4on photovoltaics using MoO3 interfacial layer,” Nano Le(. 11, 2955 (2011). Brown, P.R. et al. ACS Nano, in prep. Bozyifit, D et al, “Study of Field Driven Electroluminscence in Colloidal Quantum Dot Solids,” J. App. Phy., 113701 (2012). Coupled J-aggregating molecules exhibit high absorption, narrow emission, and small Stokes shift. !# DF)..9,.)/,1,3;77;8- 2.0 SJ2 MJ 0.0 -2.5 -5.0 -7.5 -0.5 0.5 1.0 Voltage ( V ) 1.5 &# # !"# DBP 1.5 ClAlPc G8-83,91)6789:/;8- A;B/01C1%'1-3 0.5 2.0 "## ""# ()*+,-./012-34 $## $"# Fluorescence Enhancement The fluorescence of the organic dye DCM is enhanced when resonantly coupled to a strongly optically absorbing structure consisting of a thin film of molecular J-aggregates in a critically coupled resonator. J-‐Aggregate Photo-‐detector 1.0 0.0 0.0 '# %# 5.0 SJ1 DE)..9,.)/,1)6789:/;8- =08/8+>3;-,7?,-?,1;-/,-7;/@ Stacked multijunction photovoltaics take advantage of narrow absorption features in organics and non-spatially-uniform optical intensity to more efficiently utilize the broadband solar spectrum. 2.5 J-‐aggregates and Op.cal Devices 56789:/;8-12<4 Noncontact-‐based nanoelectromechanical switches operate via tunneling/ percolation through a compressible organic layer controlled by electrostatically driven mechanical compression. Mul.junc.on Organic PV Extinction Coefficient Thin (~100 nm) gold membranes on cavity-patterned silicon dioxide substrates are fabricated for MEMS applications. Squeezable Switch (Squish) 2 Contact Printed Gold Membrane Organic Photovoltaics (OPVs) Current Density ( mA/cm ) Microelectromechanical Systems (MEMS) Jean, J. et al, “ZnO Nanowire Arrays for Enhanced Photocurrent in PbS Quantum Dot Solar Cells,” Adv. Mat., in prep. C60 400 500 600 700 800 900 Wavelength ( nm ) Macko, J. et al, “Multijunction Organic Photovoltaics with a Broad Spectral Response,” Phys. Chem. Chem. Phys. (2012). With their narrow absorption features, J-aggregates can be used to fabricate wavelength-resolved thin-film photodetectors. Organic PV on paper substrates In collaboration with the Gleason group in chemical engineering we fabricate functional organic PVs on paper. Murarka, A. et al, “Printed MEMS Membranes on Silicon,” MEMS, 2012 IEEE Int. Conf., 309 (2012) . Paydavosi, S. et al, “MEMS Switches Employing Active Metal-polymer Nanocomposites,” MEMS, 2012 IEEE Int. Conf., 180 (2012) . Barr, C. et al, “Direct Monolithic Integration of Organic Photovoltaic Circuits on Unmodified Paper,” Adv. Mat. 23, 3500 (2011). Osedach, T. et al, “Near-infrared Photodector Consisting of Jaggregating Cyanine Dye and Metal Oxide Thin Films,” App. Phy. Lett. 101, 113303 (2012). Akselrod, G. et al, “20-fold Enhancement of Molecular Fluorescence by Coupling to a J-Aggregate Critically Coupled Resonator,” ACS Nano 6, 467 (2012). The ONElab Team Dr. Ronny Costi, Dr. Parag Deotare, Dr. Dong Kyun, Dr. Andrea Maurano, Dr. Tim Osedach, Dr. Annie Wang Gleb Akselrod, Patrick Brown, Wendi Chang, Matthew D’Asaro, Eletha Flores, Christina Hanson, Joel Jean, Jill Macko, Thomas Mahony, Apoorva Murarka, Farnaz Niroui, Yasuhiro Shiradaki, Katherine Song, Supran, Mun Ee Woo.