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1.
Nat Commun ; 8: 15565, 2017 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-28569753

RESUMO

How photoexcitations evolve into Coulomb-bound electron and hole pairs, called excitons, and unbound charge carriers is a key cross-cutting issue in photovoltaics and optoelectronics. Until now, the initial quantum dynamics following photoexcitation remains elusive in the hybrid perovskite system. Here we reveal excitonic Rydberg states with distinct formation pathways by observing the multiple resonant, internal quantum transitions using ultrafast terahertz quasi-particle transport. Nonequilibrium emergent states evolve with a complex co-existence of excitons, carriers and phonons, where a delayed buildup of excitons under on- and off-resonant pumping conditions allows us to distinguish between the loss of electronic coherence and hot state cooling processes. The nearly ∼1 ps dephasing time, efficient electron scattering with discrete terahertz phonons and intermediate binding energy of ∼13.5 meV in perovskites are distinct from conventional photovoltaic semiconductors. In addition to providing implications for coherent energy conversion, these are potentially relevant to the development of light-harvesting and electron-transport devices.

2.
Opt Express ; 25(9): 10704-10709, 2017 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-28468441

RESUMO

We demonstrate enhanced absorption in solar cells and enhanced light emission in OLEDs by light interaction with a periodically structured microlens array. We simulate n-i-p perovskite solar cells with a microlens at the air-glass interface, with rigorous scattering matrix simulations. The microlens focuses light in nanoscale regions within the absorber layer enhancing the solar cell. Optimal period of ~700 nm and microlens height of ~800-1000 nm, provides absorption (photocurrent) enhancement of 6% (6.3%). An external polymer microlens array on the air-glass side of the OLED generates experimental and theoretical enhancements >100%, by outcoupling trapped modes in the glass substrate.

3.
Anal Chim Acta ; 853: 563-571, 2015 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-25467504

RESUMO

Approaches to generate porous or doped sensing films, which significantly enhance the photoluminescence (PL) of oxygen optical sensors, and thus improve the signal-to-noise (S/N) ratio, are presented. Tailored films, which enable monitoring the relative humidity (RH) as well, are also presented. Effective porous structures, in which the O2-sensitive dye Pt octaethylporphyrin (PtOEP) or the Pd analog PdOEP was embedded, were realized by first generating blend films of polyethylene glycol (PEG) with polystyrene (PS) or with ethyl cellulose (EC), and then immersing the dried films in water to remove the water-soluble PEG. This approach creates pores (voids) in the sensing films. The dielectric contrast between the films' constituents and the voids increases photon scattering, which in turn increases the optical path of the excitation light within the film, and hence light absorption by the dye, and its PL. Optimized sensing films with a PEG:PS ratio of 1:4 (PEG's molecular weight Mw ∼8000) led to ∼4.4× enhancement in the PL (in comparison to PS films). Lower Mw ∼200 PEG with a PEG:EC ratio of 1:1 led to a PL enhancement of ∼4.7×. Film-dependent PL enhancements were observed at all oxygen concentrations. The strong PL enhancement enables (i) using lower dye (luminophore) concentrations, (ii) reducing power consumption and enhancing the sensor's operational lifetime when using organic light emitting diodes (OLEDs) as excitation sources, (iii) improving performance when using compact photodetectors with no internal gain, and (iv) reliably extending the dynamic range. The effect of RH on O2 sensing is also presented. Dye:EC films are sensitive to the RH, as shown by the change of the dye's PL decay time with RH at a given O2 concentration. Surprisingly, this RH sensitivity vanishes by adding PEG to EC, including by washing PEG off. In contrast, doping EC with TiO2 nanoparticles maintains the RH effect with the advantage of significant PL enhancement. This enhancement enables differentiation of <10% changes in the RH, which is unattained with the dye:EC sensing films. The results are discussed in terms of the composition, thickness, and microstructure, whether porous or nanoparticle doped, of the composite films.

4.
Anal Chim Acta ; 778: 70-8, 2013 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-23639401

RESUMO

Key issues in using organic light emitting diodes (OLEDs) as excitation sources in structurally integrated photoluminescence (PL)-based sensors are the low forward light outcoupling, the OLEDs' broad electroluminescence (EL) bands, and the long-lived remnant EL that follows an EL pulse. The outcoupling issue limits the detection sensitivity (S) as only ~20% of the light generated within standard OLEDs can be forward outcoupled and used for sensor probe excitation. The EL broad band interferes with the analyte-sensitive PL, leading to a background that reduces S and dynamic range. In particular, these issues hinder designing compact sensors, potentially miniaturizable, that are devoid of optical filters and couplers. We address these shortcomings by introducing easy-to-employ multiple approaches for outcoupling improvement, PL enhancement, and background EL reduction leading to novel, compact all-organic device architectures demonstrated for simultaneous monitoring of oxygen and pH. The sensor comprises simply-fabricated, directionally-emitting, narrower-band, multicolor microcavity OLED excitation and small molecule- and polymer-based organic photodetectors (OPDs) with a more selective spectral response. Additionally, S and PL intensity for oxygen are enhanced by using polystyrene (PS):polyethylene glycol (PEG) blends as the sensing film matrix. By utilizing higher molecular weight PS, the ratio τ0/τ100 (PL decay time τ at 0% O2/τ at 100% O2) that is often used to express S increases ×1.9 to 20.7 relative to the lower molecular weight PS, where this ratio is 11.0. This increase reduces to ×1.7 when the PEG is added (τ0/τ100=18.2), but the latter results in an increase ×2.7 in the PL intensity. The sensor's response time is <10s in all cases. The microporous structure of these blended films, with PEG decorating PS pores, serves a dual purpose. It results in light scattering that reduces the EL that is waveguided in the substrate of the OLEDs and consequently enhances light outcoupling from the OLEDs by ~60%, and it increases the PL directed toward the OPD. The multiple functional structures of multicolor microcavity OLED pixels/microporous scattering films/OPDs enable generation of enhanced individually addressable sensor arrays, devoid of interfering issues, for O2 and pH as well as for other analytes and biochemical parameters.


Assuntos
Eletrônica , Medições Luminescentes/métodos , Oxigênio/análise , Concentração de Íons de Hidrogênio , Porosidade
5.
Adv Mater ; 24(31): 4337-42, 2012 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-22786793

RESUMO

This paper demonstrates extremely efficient (η(P,max) = 118 lm W(-1) ) ITO-free green phosphorescent OLEDs (PHOLEDs) with multilayered, highly conductive poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) films as the anode. The efficiency is obtained without any outcoupling-enhancing structures and is 44% higher than the 82 lm W(-1) of similar optimized ITO-anode PHOLEDs. Detailed simulations show that this improvement is due largely to the intrinsically enhanced outcoupling that results from a weak microcavity effect.


Assuntos
Compostos de Estanho/química , Eletrodos , Substâncias Luminescentes/química , Poliestirenos/química , Solventes/química , Tiofenos/química
6.
Opt Express ; 19 Suppl 6: A1272-80, 2011 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-22109624

RESUMO

Thin microporous films were formed by dropcasting a toluene solution containing various ratios of polystyrene:polyethylene glycol blends on a glass substrate, with OLEDs on the ITO that coated the opposite side of that substrate. We demonstrate for the first time that such easily-fabricated films with surface and bulk micropores in the index-matching polystyrene can serve as random microlens-like arrays to improve forward OLED light extraction by up to ~60%. A theoretical interpretation of the angular emission profile of the device, considering the geometrical change at the substrate/air interface and the scattering by the pores within the films, was established in excellent agreement with the experiments. The use of such blended thin films provides an economical method, independent of the OLED fabrication technique, for improving the outcoupling efficiency.

7.
Opt Express ; 19 Suppl 4: A786-92, 2011 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-21747547

RESUMO

Very uniform 2 µm-pitch square microlens arrays (µLAs), embossed on the blank glass side of an indium-tin-oxide (ITO)-coated 1.1 mm-thick glass, are used to enhance light extraction from organic light-emitting diodes (OLEDs) by ~100%, significantly higher than enhancements reported previously. The array design and size relative to the OLED pixel size appear to be responsible for this enhancement. The arrays are fabricated by very economical soft lithography imprinting of a polydimethylsiloxane (PDMS) mold (itself obtained from a Ni master stamp that is generated from holographic interference lithography of a photoresist) on a UV-curable polyurethane drop placed on the glass. Green and blue OLEDs are then fabricated on the ITO to complete the device. When the µLA is ~15 × 15 mm(2), i.e., much larger than the ~3 × 3 mm(2) OLED pixel, the electroluminescence (EL) in the forward direction is enhanced by ~100%. Similarly, a 19 × 25 mm(2) µLA enhances the EL extracted from a 3 × 3 array of 2 × 2 mm(2) OLED pixels by 96%. Simulations that include the effects of absorption in the organic and ITO layers are in accordance with the experimental results and indicate that a thinner 0.7 mm thick glass would yield a ~140% enhancement.

9.
Adv Mater ; 22(37): 4157-61, 2010 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-20803757

RESUMO

A photoluminescence (PL)-based oxygen and glucose sensor utilizing inorganic or organic light emitting diode as the light source, and polythiophene: fullerene type bulk-heterojunction devices as photodetectors, for both intensity and decay-time based monitoring of the sensing element's PL. The sensing element is based on the oxygen-sensitive dye Pt-octaethylporphyrin embedded in a polystyrene matrix.


Assuntos
Fulerenos/química , Polímeros/química , Tiofenos/química , Técnicas Biossensoriais/instrumentação , Técnicas Biossensoriais/métodos , Glucose/análise , Medições Luminescentes/métodos , Oxigênio/análise , Platina/química , Porfirinas/química
10.
Lab Chip ; 10(8): 1051-6, 2010 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-20358113

RESUMO

This paper describes the development of a compact platform for simultaneous photoluminescence (PL)-based sensing of multiple bioanalytes using a lab-on-CD. The platform is based on microfluidic features generated on foamed polypropylene (PP) surfaces by ultrasonic micro-embossing, sub-micron thick organic light-emitting diode (OLED) pixels that serve as the PL excitation sources, and a compatible array of compact photodetectors (PDs). The localized heating resulting from the ultrasonic micro-embossing enables generation of flash-free micro-patterns on the foamed PP surfaces. The embossed features are designed to function as reservoirs, channels, valves, and reaction chambers, to allow, in combination with compact OLED/PD arrays, the simultaneous monitoring of glucose, lactate, ethanol, and dissolved oxygen (DO) in four separate single CD segments using a standard PC-CD player. The analytes' concentrations are determined following CD rotation for reagent mixing by measuring the DO level via the PL decay time of an oxygen-sensitive dye following an OLED excitation pulse. Glucose, lactate, and ethanol are monitored following their oxidation in sealed cells in the presence of oxygen and their specific oxidase enzyme, which results in consumption of DO. Calibration curves for each of the analytes and their concentrations in mixtures were monitored on the four separate segments of the bio-CD. The attributes and utility of the compact OLED-bio-CD-PD platform for sensitive and accurate monitoring of multiple analytes, and its potential field-deployability, are discussed.


Assuntos
Biopolímeros/análise , Técnicas Biossensoriais/instrumentação , Discos Compactos , Iluminação/instrumentação , Técnicas Analíticas Microfluídicas/instrumentação , Compostos Orgânicos/química , Polipropilenos/química , Misturas Complexas/análise , Desenho de Equipamento , Análise de Falha de Equipamento , Semicondutores
11.
Anal Chim Acta ; 568(1-2): 190-9, 2006 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-17761260

RESUMO

A compact photoluminescence (PL)-based O2 sensor utilizing an organic light emitting device (OLED) as the light source is described. The sensor device is structurally integrated. That is, the sensing element and the light source, both typically thin films that are fabricated on separate glass substrates, are attached back-to-back. The sensing elements are based on the oxygen-sensitive dyes Pt- or Pd-octaethylporphyrin (PtOEP or PdOEP, respectively), which are embedded in a polystyrene (PS) matrix, or dissolved in solution. Their performance is compared to that of a sensing element based on tris(4,7-diphenyl-l,10-phenanthroline) Ru II (Ru(dpp)) embedded in a sol-gel film. A green OLED light source, based on tris(8-hydroxy quinoline Al (Alq3), was used to excite the porphyrin dyes; a blue OLED, based on 4,4'-bis(2,2'-diphenylviny1)-1,1'-biphenyl, was used to excite the Ru(dpp)-based sensing element. The O2 level was monitored in the gas phase and in water, ethanol, and toluene solutions by measuring changes in the PL lifetime tau of the O2-sensitive dyes. The sensor performance was evaluated in terms of the detection sensitivity, dynamic range, gas flow rate, and temperature effect, including the temperature dependence of tau in pure Ar and O2 atmospheres. The dependence of the sensitivity on the preparation procedure of the sensing film and on the PS and dye concentrations in the sensing element, whether a solid matrix or solution, were also evaluated. Typical values of the detection sensitivity in the gas phase, S(g) identical with tau(0% O2)/tau(100% O2), at 23 degrees C, were approximately 35 to approximately 50 for the [Alq3 OLED[/[PtOEP dye] pair; S(g) exceeded 200 for the Alq3/PdOEP sensor. For dissolved oxygen (DO) in water and ethanol, S(DO) (defined as the ratio of tau in de-oxygenated and oxygen-saturated solutions) was approximately 9.5 and approximately 11, respectively, using the PtOEP-based film sensor. The oxygen level in toluene was measured with PtOEP dissolved directly in the solution. That sensor exhibited a high sensitivity, but a limited dynamic range. Effects of aggregation of dye molecules, sensing film porosity, and the use of the OLED-based sensor arrays for O2 and multianalyte detection are also discussed.

12.
Biosens Bioelectron ; 19(6): 547-56, 2004 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-14683638

RESUMO

A monoclonal antibody (MAb)-gold biosensor chip with low-temperature laser-induced fluorescence detection for analysis of DNA-carcinogen adducts is described. Optimization of the detection limit, dynamic range, and biosensing applicability of the MAb-gold biosensor chip was achieved by: (1) using dithiobis(succinimidyl propionate (DSP)) as a protein linker and (2) employing recombinant protein A to provide oriented immobilization of the MAbs. The use of DSP, which has a short methylene chain length, led to faster protein binding kinetics and higher protein surface density than a longer dithiobis(succinimidyl undecanoate) (DSU) linker. The incorporation of recombinant protein A increased the distance between the oriented MAb-bound analytes and the gold surface. The increased distance minimized fluorescence quenching, resulting in about a 10-fold increase in the fluorescence signal in comparison with a chip without protein A. The improved chip architecture was used to demonstrate that biosensing of two structurally similar benzo[a]pyrene (BP)-derived DNA adducts, BP-6-N7Gua and BP-diolepoxide-10-N2dG, bound to two specific MAbs immobilized from a mixture at the same address on the chip, is feasible. These mutagenic adducts are formed by one-electron oxidation and monooxygenation pathways, and are depurinating and stable DNA adducts, respectively. It is shown that the DNA adducts can be easily identified at the same address using time-resolved, low-temperature laser-based fluorescence spectroscopy. The current limit of detection is in the low femtomole range. These results indicate that a single biosensor chip consisting of a Au/DSP/protein A/MAb nano-assembly, with analyte-specific MAbs and low-temperature fluorescence detection should be suitable for simultaneous detection and quantitation of the above adducts, as well as the luminescent antigens for which selective MAbs exist.


Assuntos
Benzo(a)pireno/análise , Técnicas Biossensoriais/instrumentação , Carcinógenos/análise , Adutos de DNA/análise , Fluorimunoensaio/instrumentação , Guanina/análogos & derivados , Benzo(a)pireno/química , Benzopirenos/análise , Benzopirenos/química , Técnicas Biossensoriais/métodos , Carcinógenos/química , Temperatura Baixa , Adutos de DNA/química , Desenho de Equipamento , Análise de Falha de Equipamento , Fluorimunoensaio/métodos , Guanina/análise , Guanina/química , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Espectrometria de Fluorescência/instrumentação , Espectrometria de Fluorescência/métodos
13.
Anal Chem ; 74(24): 6383-91, 2002 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-12510763

RESUMO

The performance of quartz crystal oscillator-based volatile organic compound (VOC) sensors has been enhanced by using coatings made from poly(styrene-block-ethylene-co-butylene-block-styrene) block copolymers blended with resins and homopolymers. Enhanced performance is characterized by a wider operational temperature range (-10 to +50 degrees C) over which the sensors displayed, concurrently, an analyte sensitivity of >0.2 Hz/ppm toluene, minimal energy loss (resistance <120 ohms), and response times of <20 min (time required to reach 90% of full response). Atomic force microscopy images are consistent with a process in which the additive associates with the polystyrene portions of the microphase-separated block copolymer. This association reinforces the rigidity of the polystyrene network while allowing the rapid uptake of VOCs by the softer polyethylene/butylene phase.


Assuntos
Poluentes Atmosféricos/análise , Monitoramento Ambiental/instrumentação , Polímeros/química , Quartzo , Tolueno/análise , Microscopia de Força Atômica , Polienos/química , Polietileno/química , Poliestirenos/química , Temperatura , Tolueno/química
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