For photovoltaic biointerfaces AgBiS2 quantum dots (QDs) offer favorable properties such as two-orders of magnitude higher absorption coefficient at near-infrared (NIR) in comparison with silicon for ultra-thin and flexible device formation and non-toxic material content. We demonstrate AgBiS2 QD based photovoltaic biointerface that stimulates cells within the spectral tissue transparency window by using NIR light (λ = 780 nm). The biointerface converts light energy below the ocular safety limit of light exposure to safe capacitive photocurrents that leads to reproducible action potentials on primary hippocampal neurons with high success rates.
Disk lasers offer the beneficial properties of low thermal lensing, excellent heat dissipation, and the amplification of ultrashort pulses. Biomaterials can be used to produce flexible and wearable devices due to their suitable mechanical characteristics and non-toxicity. In this study, we demonstrate biomaterial disk lasers using the suppression of the coffee stain effect. They show whispering gallery mode laser emission with low threshold levels below 10 nJ/µm2. Their modes and threshold levels are controlled by varying the size of the disks. They are transferrable on curved surfaces and still continue their operation on those surfaces.
Biointerfaces based on photovoltaic substrates has gained substantial attention for neural photostimulation[1, 2]. The control of Faradaic and capacitive charge transfer mechanisms by these substrates is important for effective and safe photostimulation of neurons. Faradaic mechanism uses charge transfer between electrode and electrolyte with oxidation and reduction reactions, and capacitive mechanism electrostatically perturb local ion concentration in the electrode/electrolyte interface[3, 4]. In this study, we show the control of light-activated Faradaic and capacitive charge transfer mechanisms by bulk heterojunction photovoltaic biointerfaces. We tuned the strength of the mechanisms via spatial control of the photogenerated electrons and holes in the biointerface architecture. For that, we explored three different architectures (Fig. 1) using intermediate ZnO and MoOx layers and without any intermediate layer between the transparent metal oxide (ITO) and photoactive layer. The photoactive layer is composed of organic-inorganic ternary blend of poly(3-hexylthiophene-2,5-diyl (P3HT), [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) and PbS quantum dots that lead to strong displacement currents. Moreover, we observed that integration of PbS quantum dots in the active blend of P3HT:PCBM enhances both capacitive and faradaic photocurrents due to well-aligned energy diagram, stronger absorption and better surface morphology. To characterize the photostimulation, we seeded SHSY-5Y cells on our biointerfaces and recorded the membrane depolarization of single cells. The results are also supported by two-domain stimulation model[4, 5].
KEYWORDS: Neurons, Quantum dots, Optoelectronics, Photostimulation, Spatial resolution, In vitro testing, In vivo imaging, Absorption, Organic semiconductors, Group III-V semiconductors
A large number of health problems, such as diabetes, hearing loss and retinal degeneration, can be cured by stimulation of neurons. One of the effective strategies for neural stimulation is through light-induced photoactive surfaces owing to the non-invasive and remotely accessible characteristics of light. Quantum dots are suitable candidate for such applications due to their absorption of visible light, bandgap tunability through quantum confinement effect and ease of integration into device structures due to their nanoscale size. In this study, we show that proper engineering of quantum dot nanostructure and band alignment of optoelectronic biointerface allow for bidirectional optical stimulation of neurons with high level control on stimuli strength.
Colloidal quantum dots (QDs) are intriguing materials due to their outstanding properties like spectral tunabilty, high quantum efficiency, narrow emission spectra and solution processability. Many past and on-going researches on quantum dot light-emitting devices (QLEDs) have led to achieving efficiency levels comparable to organic LEDs and semiconductor LEDs. However, most QLED studies are based on toxic QDs, which raises concerns about environmental and health issues. Our study demonstrates the application of a new non-toxic nanomaterial, InP/ZnO QDs, to LEDs. Integrating InP/ZnO QDs into device architecture, we produced low turn-on voltage (2.8 V), saturated color devices, which have luminance levels (600 cd/m2) suitable for display technology.
For high-quality general lighting, a white light source is required to exhibit good photometric and colorimetric
performance along with a high level of electrical efficiency. For example, a warm white shade is desirable for indoors,
corresponding to correlated color temperatures ≥4000 K, together with color rendering indices ≥90. Additionally, the
luminous efficacy of optical radiation (LER) should be high, preferably ≥380 lm/Wopt. Conventional white LEDs cannot
currently satisfy these requirements simultaneously. On the other hand, color-conversion white LEDs (WLEDs)
integrated with quantum dots (QDs) can simultaneously reach such high levels of photometric and colorimetric
performance. However, their electrical efficiency performance and limits have been unknown. To understand their
potential of luminous efficiency (lm/Welect), we modeled and studied different QD-WLED architectures based on layered
QD films and QD blends, all integrated on blue LED chips. The architecture of red, yellow and green emitting QD films
(in this order from the chip outwards) is demonstrated to outperform the rest. In this case, for photometrically efficient
spectra, the maximum achievable LE is predicted to be 327 lm/Welect. Using a state-of-the-art blue LED reported with a
power conversion efficiency (PCE) of 81.3%, the overall WLED PCE is shown to be 69%. To achieve LEs of 100, 150
and 200 lm/Welect, the required minimum quantum efficiencies of the color-converting QDs are found to be 39, 58 and
79%, respectively.
We present a novel dual-operation InGaN/GaN based quantum optoelectronic device (QOD) that operates as a quantum electroabsorption modulator in reverse bias and as a light emitter in forward bias in the spectral range of near-ultraviolet (UV). Here we report the design, epitaxial growth, fabrication, and characterization of such QODs that incorporate ~2-3 nm thick InGaN/GaN quantum structures for operation between 380 nm and 400 nm. In reverse bias, our QODs show an optical absorption coefficient change of ~14000 cm-1 with a reverse bias of 9 V (corresponding to ~40 cm-1 absorption coefficient change for 1 V/&mgr;m field swing) at 385 nm, reported for the first time for InGaN/GaN quantum structures in the near-UV range. In forward bias, though, our QODs exhibit optical electroluminescence spectrum centered around 383 nm with a full width at half maximum of 20 nm and photoluminescence spectrum centered around 370 nm with a full width at half maximum of 12 nm. This dual operation makes such quantum optoelectronic devices find a wide range of optoelectronics applications both as an electroabsorption modulator and a light emitting diode (LED).
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