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Quasi-2D perovskite is considered as a promising candidate for blue perovskite light emitting diode (PeLEDs). However, the wide distribution of low-order phases, inefficient energy transfer, and defects/traps increase the non-radiative recombination, further aggravating PeLED external quantum efficiency (EQE). We demonstrate a unique quasi-2D perovskite with low-order phase suppression and defect passivation by incorporating a 2D perovskite and an excess ammonium salt into the quasi-2D perovskite. By optimizing the new quasi-2D perovskites, we achieve blue PeLEDs with brightness 1765 cd m-2, EQE 7.51%, low turn-on voltage 3.07 V, and long operation lifetime 3961 sec without any shift in electroluminescent spectra.

Hole transport layer (HTL) plays a critical role for achieving high performance solution-processed optoelectronics including organic electronics. For organic solar cells (OSCs), the inverted structure has been widely adopted to achieve prolonged stability. However, there are limited studies of p-type inorganic semiconductor-based effective HTL on top of organic active layer (hereafter named as top HTL) for inverted OSCs. Currently, the p-type top HTLs are mainly two-dimensional (2D) materials, which have vertical conduction limitation intrinsically and is too thin to function as practical HTL for large area optoelectronic applications. Here, we demonstrate a novel self-assembled quasi three-dimensional (3D) nanocomposite as a p-type top HTL [1]. Remarkably, the novel HTL achieves ~15 times enhanced conductivity and ~16 times extended thickness compared to the 2D counterpart. By applying this novel HTL in inverted OSCs covering fullerene and non-fullerene systems, device performance is significantly improved. The champion power conversion efficiency (PCE) reaches 12.13%, which is the highest reported performance of solution processed HTL based inverted OSCs. Furthermore, the stability of OSCs is dramatically enhanced compared with conventional devices. The work contributes to not only evolving the highly stable and large scale OSCs for practical applications but also diversifying the strategies to improve device performance. [1] J. Cheng, H. Zhang, Y. Zhao, J. Mao, C. Li, S. Zhang, K.S. Wong, J. Hou, W.C. H. Choy, "Self-assembled Quasi-3D Nanocomposite: A Novel p-Type Hole Transport Layer for High Performance Inverted Organic Solar Cells", Adv Funct. Mater., DOI:10.1002/adfm.201706403.

Recently, researchers have focused more to design highly efficient flexible perovskite solar cells (PVSCs), which enables the implementation of portable and roll-to-roll fabrication in large scale. Here, we demonstrated that vacuum-assisted thermal annealing can be used to control the composition, morphology, and thus the quality of the perovskite films formed from the precursors of PbCl2 and CH3NH3I. Using our vacuum-assisted thermal annealing approach to completely remove the chlorine byproduct, pure, pore-free planar CH3NH3PbI3 films with enhanced morphology can be readily formed for high efficiency PVSCs with high stability and reproducibility. In addition, we will report new room temperature approaches for forming PVSCs. Regarding the hole transport layer (HTL), NiOx is a promising material for candidate for fabricating efficient PVSCs. Here, we demonstrate the flawless and surface-nanostructured NiOx film from a simple and controllable room-temperature solution process. Meanwhile, we will propose a new room temperature scheme formation of perovskite films with the features of PbI2 residue-free, large grain-sizes, and highly crystalline. We further layout the design rules for the broad, rational extension of our scheme to form high-quality perovskite films. Using our approach, a room-temperature processed PVSC is obtained with no hysteresis, high power conversion efficiency of about 18%, which is the best of the PVSCs fabricated by low-temperature techniques to date. Additionally, the device is very stable with performance maintance of 95% after 1000 hours. This work contributes to the large-sale and low-cost production of PVSCs with high device performances.

This paper reports the development of a remote laboratory (RemoteLab) platform for practising technologyenhanced learning of optics. The development of RemoteLab enhances students' understanding of experimental methodologies and outcomes, and enable students to conduct experiments everywhere at all times. While the initial goal of the system was for physics major undergradutes, the sytem was also made available for senior secondary school students. To gauge the impact of the RemoteLab, we evaluated two groups of students, which included 109 physics 1st-year undergraduates and 11 students from a local secondary school. After the experiments, evaluation including questionnaire survey and interviews were conducted to collect data on students' perceptions on RemoteLab and implementation issues related to the platform. The surveys focused on four main topics, including user interface, experiment setup, booking system and learning process. The survey results indicated that most of the participants’ views towards RemoteLab was positive.

The lead halide-based perovskite solar cells have emerged as a promising candidate in photovoltaic applications. However, the precise control over the morphologiy of the perovskite films (minimizing pore formation) and enhanced stability and reproducibility of the devices remain challenging, even though both will be necessary for further advancements. Here we introduce vacuum-assisted thermal annealing as a means of controlling the composition and morphology of the CH3NH3PbI3 films formed from PbCl2 and CH3NH3I as precursors. We identify the critical role that the CH3NH3Cl generated as a byproduct during the pervoskite synthesis plays for the photovoltaic performance of the perovskite film. Removing this byproduct through vacuum-assisted thermal annealing we succeeded in producing pure, pore-free planar CH3NH3PbI3 films showing high conversion efficiency (PCE) reaching 14.5%). Removal of CH3NH3Cl strongly attenuate the photocurrent hysteresis.

As the intrinsic electrostatic limit, space charge limit (SCL) for photocurrent is a universal phenomenon which is fundamental important for organic semiconductors. We will demonstrate SCL breaking by a new plasmonic-electrical concept. As a proof-ofconcept, organic solar cells (OSCs) comprising metallic planar and grating electrodes are studied. Interestingly, although strong plasmonic resonances induce abnormally dense photocarriers around a grating anode, the grating incorporated inverted OSC is exempt from space charge accumulation (limit) and degradation of electrical properties. The plasmonic-electrical concept will open up a new way to manipulate both optical and electrical properties of semiconductor devices simultaneously.

Bragg scattering by one dimensional periodic structures is investigated in order to enhance the outcoupling effciency of optically optimized planar top-emitting OLEDs. Using a soft imprint process, we fabricate extremely homogeneous gratings with sub- m period. These gratings are integrated beneath the bottom contact of topemitting OLEDs, without affecting the electrical device performance. The reflective contacts of the top emission geometry introduce pronounced micro-cavity effects for directly outcoupled and internally trapped light modes. Bragg scattering of the trapped waveguided and surface plasmon modes into the air cone, i.e. the forward direction, leads to interference with the directly outcoupled mode. As a result, constructive and destructive interference of the modes is detected and analyzed. Overall, we find that the introduction of shallow one dimensional sub- m periodic grating structures underneath top-emitting OLEDs leads to an EQE and luminous efficacy enhancement by up to 42%.

Typically, most low bandgap materials have low absorption with wavelength at around 500 nm. Besides, the restrictions of active layer thickness of thin film organic solar cells (OSCs) make the devices reduce to absorb light in long wavelength region (around 700 nm). As absorption would be a joint effect of material band properties and optical structures, well-designed light-trapping strategies for these low-bandgap PSCs will be more useful to further enhance efficiencies. We investigate the change of optical properties and device performances of organic solar cells based on our newly synthesized low-bandgap material with embedded poly-(3,4-ethylenedioxythiophene): poly(styrenesulfonate) PEDOT:PSS grating in the photoactive bulk heterojunction layer.

Although various optical designs and physical mechanisms have been studied both experimentally and theoretically to improve the optical absorption of organic solar cells (OSCs) by incorporating metallic nanostructures, the effects of plasmonic nanostructures on the electrical properties of OSCs is still not fully understood. Hence, it is highly desirable to study the changes of electrical properties induced by plasmonic structures and the corresponding physics for OSCs. In this work, we develop a multiphysics model for plasmonic OSCs by solving the Maxwell’s equations and semiconductor equations (Poisson, continuity, and drift-diffusion equations) with unified finite-difference method. Both the optical and electrical properties of OSCs incorporating a 2D metallic grating anode are investigated. For typical active polymer materials, low hole mobility, which is about one magnitude smaller than electron mobility, dominates the electrical property of OSCs. Since surface plasmon resonances excited by the metallic grating will produce concentrated near-field penetrated into the active polymer layer and decayed exponentially away from the metal-polymer interface, a significantly nonuniform and extremely high exciton generation rate is obtained near the grating. Interestingly, the reduced recombination loss and the increased open-circuit voltage can be achieved in plasmonic OSCs. The physical origin of the phenomena lies at direct hole collections to the metallic grating anode with a short transport path. In comparison with the plasmonic OSC, the hole transport in a multilayer planar OSC experiences a long transport path and time because the standard planar OSC has a high exciton generation rate at the transparent front cathode. The unveiled multiphysics is particularly helpful for designing high-performance plasmonic OSCs.

To enhance the light trapping of organic solar cells (OSCs), metallic (e.g. Au, Ag) nanoparticles (NPs) have been incorporated into the polymer layers conveniently in solution process. Although power conversion efficiency (PCE) of OSCs has been shown to improve by incorporating metallic NPs in either the buffer layer such as poly-(3,4-ethylenedioxythiophene) :poly(styrenesulfonate) (PEDOT:PSS)[1] or the active layer[2], the understanding on the changes is still not quite clear. Moreover, there are very limited studies on incorporating metallic NPs in more than one organic layer and investigating their effects on the optical and electrical properties as well as the performances of OSCs. In this work, monofunctional poly(ethylene glycol) (PEG)-capped Au NPs of sizes 18 nm and 35 nm are doped in the PEDOT:PSS and poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) layers respectively, leading to an improvement of PCE by ~22% compared to the optimized control device. We will firstly identify the impact of NPs in each polymer layer on OSC characteristics by doping Au NPs in either the PEDOT:PSS or P3HT:PCBM layer. Then, we will investigate Au NPs incorporated in all polymer layers. We demonstrate that the accumulated benefits of incorporating Au NPs in all organic layers of OSCs can achieve larger improvements in OSC performances.

In this work, we focus on introducing an alternative approach to realize transparent graphene anodes. We report the use of very thin thermally evaporated gold (Au) nanoclusters with proper UVO treatments to facilitate efficient hole collection at graphene electrodes, which significantly benefits device performance while avoiding issues arising from PEDOT:PSS. We will investigate the effects of Au thickness and UVO treatments for optimizing device performance. Ultraviolet photoemission spectroscopy (UPS) is conducted to further analyze the WF shift at the graphene/polymer interface modified by UVO-treated Au.

Bright and efficient stacked color-tunable organic light emitting devices (OLEDs) using an intermediate Al/Au electrode have been reported. The effects of the thicknesses of Al and Au layers on the luminance characteristics have been comprehensively studied. After optimization, the bottom-emission single-unit OLED of 4,4′,4′′-Tris(N-3-methylphenyl-N-phenyl-amino) triphenylamine/N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine/tris(8-hydroxyquinoline) aluminum has a maximum luminance efficiency (ηL) of 3.37 cd/A by using Al/Au as the cathode and 2.92 cd/A by using Al/Au as the anode. Meanwhile, by introducing the optimized intermediate Al/Au electrode into the stacked color-tunable (red to blue) OLEDs, a red unit with maximum ηL of 4.73 cd/A and a blue unit with maximum ηL of 3.96 cd/A have been obtained. The color can be tuned efficiently along a linear route from pure red with the Commission Internationale de l’Eclairage (CIE) coordinates of (0.662, 0.330) to sky blue with the CIE coordinates of (0.155, 0.340). This scheme can be a potential candidate for achieving high-brightness and efficient stacked color-tunable OLEDs.

By engineering a new cohosting system of tris(8-hydroxyquinoline) and 4,7-diphenyl-1,10-phenanthroline in the electron transport layer, the cu rrent efficiency of the organic light emitting diode is improved by more than 20% while the bias is reduced by ~40% as compared to the device with a single host of Alq 3 as the electron transport layer. The maximum luminance is over 16000 cd/m 2 at the bias of 22V and the current of 475mA/cm , which is ~73% higher than the single host Alq 3 device without optimizing the layer thickness. The lifetime under ambient environment is enhanced by a factor of ~1.8. The reasons for the improveme nt will be investigated. The results strongly indicate that the knowledge of bulk conductivity engineering of organic n-type transporters shows practical significance in OLED applications. Keywords: Tris (8-hydroxyquinoline) aluminum, 1,10-phenanthro line, mobility, electron transport, co-host 1. INTRODUCTION Tris (8-hydroxyquinoline) aluminum (Alq

Electroluminescent bipolar small molecules have been attracted with great interests recently. They are found to exhibit many interesting features such as (i) reducing the structural complexity of organic light emitting diodes (OLEDs) from multilayer heterojunction to monolayer homojunction devices; (ii) offering molecular p/n junction, and (iii) minimizing the formation of exciplexes. In this paper, the optical and electrical properties of novel oxadiazole-triphenylamine derivatives will be investigated. The derivatives are N-phenyl-N-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)phenylamine (POT) and N-phenyl-N-(4-(5-p-tolyl-1,3,4-oxadiazol-2-yl)phenyl)phenylamine (m-POT). The absolute absorption coefficient and refractive index have been investigated by ellipsometry and modeling. The electron mobility of POT at room temperature has been studied. The results show that the derivatives have bipolar characteristics. The electron-transporting properties of POT is better than that of m-POT. The EL emission peaks of POT and m-POT are the same at 435nm which match with their photoluminescent (PL) peaks.

In this paper, the effects of hole injection layer (HIL) on the performance of typically used tris-(8-hydroxyquinoline) aluminum (Alq 3 ) based OLEDs have been investigated. Three different HIL materials were used: copper phthalocyanine (CuPc), magnesium phthalocyanine (MgPc) and zinc phthalocyanine (ZnPc). The Metallophthalocyanines (MPcs) will be used to construct single hole injection layer (HIL) and double HIL ( d -HIL). In the OLEDs, Alq 3 acts as the emitting layer and electron transport layer. Although d -HIL structures show higher efficiency than that of the reference device, the highest current efficiency ~ 4.02 cd/A corresponds to the 15 nm ZnPc HIL device. Compared to an current efficiency of ~3.29 cd/A and a power efficiency of ~0.99 lm/W (at 100 cd/m 2 luminance) of the reference device, an 15 nm ZnPc HIL device has ~22% higher current efficiency and ~67% higher power efficiency. The reasons for the improvements will be discussed.

Laterial p-i-n photodiodes have been produced in a standard, unmodified commercial GaAs integrated circuit process (Vitesse Semiconductor Inc. HGaAs IV and V). The devices were modelled using the MEDICI simulation package, achieving a very good fit to both capacitance and DC light response measuremnts. The simulation recreated an interesting feature of the devices, wherein the detectors go from a low-performance to high-performance regime abruptly at a specific reverse bias. An analysis of the simulated behavior of the depletion region in the nominally intrinsic region of the device provided a partial answer to the physics behind this bias point. A second generation of devices of different geometries was fabricated and tested. The newer fabrication process showed a lower performance transition (~0.6 V) than the previous process (~4 V) for an identical layout geometry. Preliminary high-speed measurements of the newer devices are quite encouraging.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Diffused quantum wells (DFQW) optical devices have been widely investigated for use in optical electronics integrated circuits. In this paper, we report on the performance of five-period DFQW optical amplifiers and modulators. The result show that the QW amplifiers and modulators maintain at single guiding mode operation after the QW structure has been annealed. The running range of the operation l wavelength of QW optical amplifiers is 34 meV without a significant degradation in the modal gain peak by interdiffusing the QWs. The QW interdiffusion was accomplished by P + ion implantation to the upper region of the top cladding layer of the multilayer structure and followed by rapid thermal annealing such that the implanted ions did not damage the QW structures. The I-V characteristics of the implanted QW are similar to that of the unimplanted. Concerning the TE electro-absorptive modulation, a large contrast ratio of 35dB can be obtained at (lambda) op equals 1.55 micrometers under a small bias of -1.5V fora 500 micrometers long modulator. For TM mode, a slightly higher CR Of 37dB can be obtained at the operation wavelength although the reverse bias voltage is double.

A theoretical study of the polarization independent quantum-well gain using interdiffusion is presentedhere. Group V sublattice interdiffusion in InGaAs/InP quantum wells is used to produce polarizationindependent optical gain. The reverse bias and carrier effects on the subband structures, transition energy and optical gain of the interdiffused quantum well are discussed. The interdiffused quantum well structures are optimized in terms of their subband structure, carrier density, structural parameters and properties of optical gain spectra. The results show that an optimized interdiffused quantum well structure can produce polarization independent optical gain over a range of operation wavelengths around 1.5jim, although the differential gain and linewidth enhancement factor are slightly degraded. The required tensile strain for the polarization independence of a lattice-matched quantum well structure isgenerated here using interdiffusion. These results suggest that polarization independent optical devicescan be fabricated using interdiffusion using a lattice-matched InGaAsP quantum well structure.KEYWORDS: optical polarization independence QW, electro-absorption, optical gain, quantum wellamplifier, diffused quantum well, carrier effects, reverse bias effects

Electro-optic modulators using the interaction of surface acoustic waves (SAWs) with III-V semiconductor multiple quantum well structures have gained interests. A SAW induces potential field which provides the phase modulation. In order to improve the phase modulation, an AlGaAs/GaAs asymmetric double quantum well (DQW) optical phase modulator using SAWs is investigated theoretically. The optimization steps of the DQW structure are discussed. The optimized phase modulator structure is found to contain a five-period DQW active region. Analysis of the modulation characteristics show that by using the asymmetric DQW, the large change of the induced potential at the surface and thus large modification of the QW structure can be utilized. The modification of each QW structure is consistent, although this consistency is not always preserved in typical SAW devices. Consequently, the change of refractive index in each of the five DQWs is almost identical. Besides, the change of effective refractive index is 10 times larger here in comparison to a modulator with a five periods single QW as the active region and thus produces a larger phase modulation. In addition, a long wavelength and a low SAW power required here increase the size of the SAW transducer and simplify its fabrication.

The characteristics of Al 0.3 Ga 0.7 As/GaAs QW acousto- absorption and acousto-optic modulators using the interaction between surface acoustic wave (SAW) and quantum well (QW) optical waveguide structures are analyzed here theoretically. The QW structures are optimized by maximizing the optical confinement of modal field in the active region and the piezoelectric effect of SAW and QWs. The electric field induced by SAW reduces non-uniformly in depth, which limits in the development of high efficiency modulators, especially for devices with a large number of QWs in the active region. For devices with thin active regions, the QW structures are designed so that at the top surface strong SAW effects can be obtained while for the 25 periods structure, the QWs located at a depth of 2/3 SAW wavelength in order to obtain an uniform SAW induced electric field. The results show that the single and five QW devices are suitable for absorptive modulation and optical modulation respectively while the 25-QW modulators can shorten the modulation interaction length and thus increase modulation bandwidth. The effective index change of these devices are at least 10 times larger than the conventional surface acoustic wave devices. These result make the quantum-well modulators more attractive for the development of acousto- optic device applications.

This paper examines the current NCAR MSS, MSS use requirements, a possible optical systems design, MSS magnetic-to-optical conversion plans, and some cost considerations.