Professor Robert Taylor

Abstract:

Halide perovskite light-emitting diodes (PeLEDs) exhibit great potential for use in next-generation display technologies. However, scale-up will be challenging due to the requirement of very thin transport layers for high efficiencies, which often present spatial inhomogeneities from improper wetting and drying during solution processing. Here, we show how a thin Al2O3 layer grown by atomic layer deposition can be used to preferentially cover regions of imperfect hole transport layer deposition and form an intermixed composite with the organic transport layer, allowing hole conduction and injection to persist through the organic hole transporter. This has the dual effect of reducing nonradiative recombination at the heterojunction and improving carrier selectivity, which we infer to be due to the inhibition of direct contact between the indium tin oxide and perovskite layers. We observe an immediate improvement in electroluminescent external quantum efficiency in our p-i-n LEDs from an average of 9.8% to 13.5%, with a champion efficiency of 15.0%. The technique uses industrially available equipment and can readily be scaled up to larger areas and incorporated in other applications such as thin-film photovoltaic cells.

Abstract:

The optical modal gain of Cd_0.6Zn_0.4Te/ZnTe double quantum dots was measured using a variable stripe length method, where large and small quantum dots are separated with a ZnTe layer. With a large (~18 nm) separation layer thickness of ZnTe, two gain spectra were observed, which correspond to the confined exciton levels of the large and small quantum dots, respectively. With a small (~6 nm) separation layer thickness of ZnTe, a merged single gain spectrum was observed. This can be attributed to a coupled state between large and small quantum dots. Because the density of large quantum dots (4 × 10¹⁰ cm⁻²) is twice the density of small quantum dots (2 × 10¹⁰ cm⁻²), the density of the coupled quantum dots is determined by that of small quantum dots. As a result, we found that the peak gain (123.9 ± 9.2 cm⁻¹) with the 6 nm separation layer is comparable to that (125.2 ± 29.2 cm⁻¹) of the small quantum dots with the 18 nm separation layer.

Abstract:

A piezoelectric energy generating device that produces electricity using plasmon-enhanced solar radiation pressure (SRP) is developed. The SRP is greatly enhanced on the operational region of the device with a unique crater-like structure, and direct current is generated successfully on the device. By optimizing the material and thickness of top electrode, a maximum power density of 396 µW cm−2 is obtained. In addition, by using Raman measurements, finite-difference time-domain simulation, and COMSOL Multiphysics analysis, it is confirmed that the SRP is greatly amplified on the operational region with the nanoscale surface roughness due to resonance between the incident light and surface plasmons. By increasing the rotational speed of an optical chopper used to measure the change in the output characteristics of the device, and comparing this with the simulated result, it is found that the constant charge produced by the piezoelectric effect arose due to the superposition of charge phases in the device.

Abstract:

2D-layered transition metal chalcogenides are useful semiconductors for a wide range of opto-electronic applications. Their similarity as layered structures offers exciting possibility to modify their electronic properties by creating new heterojunction assemblies from layer-by-layer restacking of individual monolayer sheets, however, the lack of specific interaction between these layers could induce phase segregation. Here, we employed a chemical method using n-BuLi to exfoliate MoS₂ and In₂Se₃ into their monolayer-containing colloids in solution. The bulky Se atoms can be selectively leached from In₂Se₃ during Li treatment which gives positively charged surface monolayers in neutral pH whereas the strong polarization of Mo–S with moderate S leaching gives a negatively charged surface. Specific interlayer electrostatic attraction during their selective assembly gives a controllable atomic AB-type of layer stacking as supported by EXAFS, STEM with super-EDX mapping, TAS/TRPL and DFT calculations. Using this simple but inexpensive bottom-up solution method, a new photocatalyst assembled from layers for photo water splitting can be tailor-made with high activity.

Abstract:

Experimental research data collected in laboratories at the Clarendon Laboratory, 2020-2022.