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High-performance inorganic-organic lead halide perovskite solar cells (PSCs) are often fabricated with a liquid additive such as dimethyl sulfoxide (DMSO), which retards crystallization and reduces roughness and pinholes in the perovskite layers. However, DMSO can be trapped during perovskite film formation and induce voids and undesired reaction byproducts upon later processing steps. Here, it is shown that the amount of residual DMSO can be reduced in as-spin-coated films significantly through use of preheated substrates, or a so-called hot-casting method. Hot casting increases the perovskite film thickness given the same concentration of solutions, which allows for reducing the perovskite solution concentration. By reducing the amount of DMSO in proportion to the concentration of perovskite precursors and using hot casting, it is possible to fabricate perovskite layers with improved perovskite-substrate interfaces by suppressing the formation of byproducts, which increase trap density and accelerate degradation of the perovskite layers. The best-performing PSCs exhibit a power conversion efficiency (PCE) of 23.4% (23.0% stabilized efficiency) under simulated solar illumination. Furthermore, encapsulated devices show considerably reduced post-burn-in decay, retaining 75% and 90% of their initial and post-burn-in efficiencies after 3000 h of operation with maximum power point tracking (MPPT) under high power of ultraviolet (UV)-containing continuous light exposure.

Iodine-containing volatiles are major degradation products of halide perovskite materials under irradiation, yet iodine diffusion kinetics into and throughout organic hole transport materials (HTMs...

Amorphous oxide semiconductors (AOSs), specifically those based on ternary cation systems such as Ga-, Si-, and Hf-doped InZnO, have emerged as promising material candidates for application in next-gen transparent electronic and optoelectronic devices. Third cation-doping is a common method used during the manufacturing of amorphous oxide thin film transistors (TFTs), primarily with the intention of suppressing carrier generation during the fabrication of the channel layer of a transistor. However, the incorporation of a third cation species has been observed to negatively affect the carrier transport properties of the thin film, as it may act as an additional scattering center and subsequently lower the carrier mobility from ∼20–40 cm2 V−1 s−1 of In2O3 or a binary cation system (i.e., InZnO) to ∼1–10 cm2 V−1 s−1. This study investigates the structural, electrical, optoelectronic, and chemical properties of the ternary cation material system, InAlZnO (IAZO). The optimized carrier mobility (Hall Effect) of Al-doped InZnO is shown to remain as high as ∼25–45 cm2 V−1 s−1. Furthermore, Al incorporation in InZnO proves to enhance the amorphous phase stability under thermal stresses when compared to baseline InZnO films. Thin film transistors integrating optimized IAZO as the channel layer are shown to demonstrate promisingly high field effect mobilities (∼18–20 cm2 V−1 s−1), as well as excellent drain current saturation and high drain current on/off ratios (>107). The high mobility and improved amorphous phase stability suggest strong potential for IAZO incorporation in the next generation of high performance and sustainable optoelectronic devices such as transparent displays.

While metal-halide perovskite light-emitting diodes (PeLEDs) hold the potential for a new generation of display and lighting technology, their slow operation speed and response time limit their application scope. Here, high-speed PeLEDs driven by nanosecond electrical pulses with a rise time of 1.2 ns are reported with a maximum radiance of approximately 480 kW sr-1 m-2 at 8.3 kA cm-2 , and an external quantum efficiency (EQE) of 1% at approximately 10 kA cm-2 , through improved device configuration designs and material considerations. Enabled by the fast operation of PeLEDs, the temporal response provides access to transient charge carrier dynamics under electrical excitation, revealing several new electroluminescence quenching pathways. Finally, integrated distributed feedback (DFB) gratings are explored, which facilitate more directional light emission with a maximum radiance of approximately 1200 kW sr-1 m-2 at 8.5 kA cm-2 , a more than two-fold enhancement to forward radiation output.

Solution-processed organic–inorganic hybrid perovskites have recently emerged as promising low-cost materials for optoelectronic applications. However, exposure to light or applied bias causes phas...

Possessing the ability to tune the work function and band gap of transparent conducting oxides (TCOs) is widely sought after, as it allows for improved band alignment in electronic and optoelectronic applications, enhancing overall device performance. Out of the many TCOs, Al-doped zinc oxide (AZO) has received considerable interest for electrode application due to its low electrical resistivity, high optical transparency in the visible regime, and room-temperature fabrication capability. In this study, we report on the effects of post fabrication air-annealing on the work function and band alignment of AZO deposited at room temperature by DC-magnetron sputtering. AZO films were air-annealed at temperatures varying from 25 °C (as-deposited) to 600 °C. The Fermi energy levels, work function values, surface chemistry, and optical band gaps of the AZO films were investigated via X-ray photoelectron spectroscopy (XPS) and UV–Vis spectroscopy. An increase of the work function from ~5.53 eV to ~6.05 eV is observed to take place over an increase of annealing temperatures from 25 °C (as-deposited) to 600 °C, determined to be the result of a decrease in carrier concentration through the promoted extinction of oxygen vacancies. Via XPS analysis, the increased extinction of oxygen vacancies was confirmed due to a notable shift from an oxygen-deficient state to an oxygen-sufficient state in the high resolution O 1s peaks, for which the activation energy was found to be 33.3 meV. Over the course of increasing annealing temperatures, the optical band gap saw a shift from ~3.55 eV to ~3.37 eV, following the Burstein-Moss phenomenon due to a decrease in carrier concentration, further verifying an increase in oxygen vacancy extinction. The reported results confirm that work function tuning of AZO films can be achieved through simple post-fabrication air-annealing.

Extensive research has established organic-inorganic hybrid perovskites as a promising material for optoelectronic device applications. Especially for lasers, many optically driven amplified spontaneous emission and lasing reports have been demonstrated across the near infrared to the green in various configurations (distributed feedback (DFB), distributed Bragg reflectors, photonic crystals, etc) and pumping regimes (from pulsed to continuous-wave excitation) at low threshold, allowed by the tunable bandgap energy by controlling halide stoichiometry or material dimensionality. However, most reports lack red-emitting lasing action at room temperature due to undesirable halide phase separation that produces iodide-rich and bromide-rich domains in mixed-halide perovskites under intense illumination, resulting in a ‘red gap’ problem where bandgap becomes pinned to the lower iodide-rich phase. Here we demonstrate a red-emitting 2nd-order DFB laser operating at room temperature from solution-processed organic-inorganic hybrid perovskite thin films for the first time. Ultra-flat mixed-halide perovskite layers were prepared on a quartz grating to achieve single-mode surface-emitting laser emission for at least a few tens of minutes (~ 10^6 pulses) with a threshold of 85 µJ/cm^6 and full-width-half-maximum of less than 1.5 nm under picosecond-pulsed optical excitation. We effectively suppress phase separation by properly choosing self-assembled long-chain organic ammonium halide additives to enable stable lasing action over a wide range of wavelengths near the red. Our results provide a significant step towards full-color visible laser device applications from cost-effective halide perovskite material systems.

Near-infrared (NIR) light-emitting diodes (LEDs), with emission wavelengths between 800 and 950 nm, are useful for various applications, e.g., night-vision devices, optical communication, and medical treatments. Yet, devices using thin film materials like organic semiconductors and lead based colloidal quantum dots face certain fundamental challenges that limit the improvement of external quantum efficiency (EQE), making the search of alternative NIR emitters important for the community. In this work, efficient NIR LEDs with tunable emission from 850 to 950 nm, using lead-tin (Pb-Sn) halide perovskite as emitters are demonstrated. The best performing device exhibits an EQE of 5.0% with a peak emission wavelength of 917 nm, a turn-on voltage of 1.65 V, and a radiance of 2.7 W Sr-1 m-2 when driven at 4.5 V. The emission spectra of mixed Pb-Sn perovskites are tuned either by changing the Pb:Sn ratio or by incorporating bromide, and notably exhibit no phase separation during device operation. The work demonstrates that mixed Pb-Sn perovskites are promising next generation NIR emitters. ispartof: ADVANCED MATERIALS vol:31 issue:3 ispartof: location:Germany status: published

The performance of lead-halide perovskite light-emitting diodes (LEDs) has increased rapidly in recent years. However, most reports feature devices operated at relatively small current densities ( 10% to current densities as high as 2000 mA cm-2 ), and tenfold increase in operational lifetime (when driven at 100 mA cm-2 ). Furthermore, with proper thermal management, a maximum current density of 2.5 kA cm-2 and an EQE of ≈1% at 1 kA cm-2 are shown using electrical pulses, which represents an important milestone toward electrically driven perovskite lasers.

Hybrid organic-inorganic perovskite semiconductors have shown potential to develop into a new generation of light-emitting diode (LED) technology. Herein, an important design principle for perovskite LEDs is elucidated regarding optimal perovskite thickness. Adopting a thin perovskite layer in the range of 35-40 nm is shown to be critical for both device efficiency and stability improvements. Maximum external quantum efficiencies (EQEs) of 17.6% for Cs0.2 FA0.8 PbI2.8 Br0.2 , 14.3% for CH3 NH3 PbI3 (MAPbI3 ), 10.1% for formamidinium lead iodide (FAPbI3 ), and 11.3% for formamidinium lead bromide (FAPbBr3 )-based LEDs are demonstrated with optimized perovskite layer thickness. Optical simulations show that the improved EQEs source from improved light outcoupling. Furthermore, elevated device temperature caused by Joule heating is shown as an important factor contributing to device degradation, and that thin perovskite emitting layers maintain lower junction temperature during operation and thus demonstrate increased stability.

Perovskite semiconductors are actively investigated for high performance solar cells. Their large optical absorption coefficient and facile solution-based, low-temperature synthesis of thin films make perovskites also a candidate for light-emitting devices across the visible and near-infrared. Specific to their potential as optical gain medium for lasers, early work has demonstrated amplified spontaneous emission and lasing at attractively low thresholds of photoexcitation. Here, we take an important step toward practically usable perovskite lasers where a solution-processed thin film is embedded within a two-dimensional photonic crystal resonator. We demonstrate high degree of temporally and spatially coherent lasing whereby well-defined directional emission is achieved near 788 nm wavelength at optical pumping energy density threshold of 68.5 ± 3.0 μJ/cm(2). The measured power conversion efficiency and differential quantum efficiency of the perovskite photonic crystal laser are 13.8 ± 0.8% and 35.8 ± 5.4%, respectively. Importantly, our approach enables scalability of the thin film lasers to a two-dimensional multielement pixelated array of microlasers which we demonstrate as a proof-of-concept for possible projection display applications. MOE (Min. of Education, S’pore) Accepted version

Perovskite (CH 3 NH 3 PbI 3 ) films possessing optical quality were prepared by solution-based spin-casting at room temperature. We report near infrared lasing with well-defined spatially coherent output from second-order surface-emitting distributed feedback grating structure with perovskite active media.

Red, green and blue distributed feedback lasers based on dense colloidal CdSe quantum dot thin films were optically pumped in quasi-steady state. The red lasers showed 32% internal quantum efficiency and 400 μW output power.

In this project, we: (1) demonstrated colloidal Quantum Dot (QD) based vertical-cavity surface emitting lasers (VCSELs) with record low thresholds, (2) engineered the local density of optical states (LDOS) in 1D waveguides to control the emission of randomly oriented QDs, (3) demonstrated silica cladding of commercial QDs, and thus broadened the range of QD sources suitable for on-chip integration using electrostatic self-assembly methods, (4) demonstrated a robust, reusable platform of alumina templates for the precise placement of single colloidal QDs, (5) built a custom scanning confocal microscope setup capable of performing large-scale characterization of the lifetime and g2 autocorrelation of individual QD emission in self-assembled arrays, and (6) integrated colloidal QDs in dielectric waveguides and near resonant nanostructures.

Experimental studies of amplified spontaneous emission (ASE) and lasing from various colloidal II-VI semiconductor nanocrystals have been used as inputs to several microscopic models for underlying optical gain, usually involving permutations of quantum confined multiple excitonic states. Here we focus on particular types of CdSe/ZnCdS and CdSe/ZnS/ZnCdS colloidal quantum dot (CQD) films and elucidate on the discovery of single-exciton states at the fundamental edge as a dominant mechanism for optical gain at room temperature. Pump-probe spectroscopic techniques enable us to measure the onset of gain at ensemble-average exciton occupancy per CQD, = 0.6 and 0.7 for the two types of CQD films at room temperature. Time-resolved measurements, in turn, show how optical gain persists well into the time regime associated with spontaneous emission (nanoseconds), thus providing direct evidence for how the non-radiative Auger recombination processes (~100 ps) can be thwarted. In addition to benefits of the material assets of densely packed CQD films with high luminescence efficiency (quantum yield ~90%) and nanoparticle monodispersity therein, we propose that access to the single-exciton gain regime at room temperature requires a careful spectral balance between the lowest exciton absorption resonance and its corresponding red-shifted spontaneous emission maximum (“Stokes shift”).

Epitaxial-like colloidal quantum dot films are demonstrated as potential single material system for red, green, and blue lasing. These prospects derive in part from the access to single exciton gain in the optically dense films.

Wavelength engineered nanocrystal colloidal quantum dots were used to create a thin solid films. Very low thresholds for light amplification were achieved in these red, green and blue film by a single exciton gain mechanism which also enables optical gain with quasi-steady pumping source.

We report on wavelength-variable lasing from optical gain media composed of colloidal quantum-dots (CQD) thin films across the visible spectrum. Exploiting single exciton gain enables amplified spontaneous emission (ASE) and vertical cavity lasing at very low optical pump thresholds. The average number of exciton per CQD at the ASE threshold is ∼ 0.8, which significantly reduces losses from enhanced nonradiative multiexciton Auger recombination in nanometer sized semiconductor particle, enabling quasi-continuous-wave CQD laser performance in densely packed nanocomposites.

First, it is concluded that re-designing the objective lens of system is a good method to obtain maximum performance at fixed refractive index of media. Also, two systems cutting SIL and none cutting SIL were compared as re-designing objective lens. The result says that two systems are the same practically. Therefore, in designing the system, it does not need to consider the cutting the SIL. In comparing with Opti and Hyper, Opti has more tolerance that Hyper in certain respects. Hence Opti can be a suitable system for Optical data storage. Adding to this, it is possible to minimize the error due to production process by moving the collimate lens.

Holography has a considerable advantage to retrieve the three-dimensional (3D) information of an object from only one interference recording. For several decades, the technology of digital holography (DH), which uses numerical reconstruction as opposed to illuminating the reference beam to the hologram plate, has progressed with the assistance of improvements in 2D array detectors and computers. In this paper, a dual-type inline digital hologram microscope (DHM) system that can be used with both transmission imaging and reflection imaging in a single device is developed. The proper method depending on the modes (transmission imaging or reflection imaging) can be changed easily in this system according to the characteristics of the object. Illumination with a plane wave is the necessary condition for retrieving the correct phase information. In the case of reflection imaging, unlike in transmission imaging, a special relay lens in addition to the microscope objectives (MOs) is needed to meet the needs of this condition. However, the quality of the 3D information can deteriorate significantly due to the overlapping twin image that is inherent in holography. This study suggests an effective and convenient method for eliminating the twin image that is entangled in the reconstructed information. The proposed method does not require extra components, numerical iterations, and restrictions on the object.

We demonstrate surface emitting distributed feedback (DFB) lasers across the red, green, and blue from densely packed colloidal quantum dot (CQD) films. The solid CQD films were deposited on periodic grating patterns to enable 2nd-order DFB lasing action at mere 120, 280, and 330 μJ/cm2 of optical pumping energy densities for red, green, and blue DFB lasers, respectively. The lasers operated in single mode operation with less than 1 nm of full-width-half-maximum. We measured far-field patterns showing high degree of spatial beam coherence. Specifically, by taking advantage of single exciton optical gain regime from our engineered CQDs, we can significantly suppress the Auger recombination to reduce lasing threshold and achieve quasi-steady state, optically pumped operation. Published version

Colloidal quantum dots (CQD) are now making their entry to full-color displays, endowed by their brightness and single-material base. By contrast, many obstacles have been encountered in their use towards lasers. We demonstrate here optically pumped distributed feedback (DFB) lasers, based on close-packed, solid films self-assembled from type-I CQDs. Notably, the single mode CQD-DFB lasers could reach such a low threshold as to be pumpable with a compact pulsed source in a quasi-continuous wave regime. Our results show the spatially and temporally coherent laser beam outputs with power of 400 μW and a quantum efficiency of 32%. Accepted version

Novel distributed feedback lasers were created in densely packed colloidal quantum dot single exciton gain media. The optically pumped lasers demonstrated internal efficiency of 28%, spatially coherent beams, average power of 400 μW.

We have reached the long-sought single exciton gain regime in dense colloidal II-VI semiconductor quantum dot films. Transient spectroscopy details their exciton dynamics, informing further development of single material based lasers across the visible.