arXiv subjects

Ifor D. W. Samuel

Publications and source records attributed to Ifor D. W. Samuel.

6 recordsLinked to original sources

arXiv2025

Interaction of Polymer of Intrinsic Microporosity PIM-1 with explosive analytes at the molecular level: Combined experiment and computational modelling

This work investigates the molecular-level interactions of a fluorescent microporous polymer (PIM-1) with nitroaromatic explosives, in the context of thin film explosive sensors. Thin films of the PIM-1 were exposed to 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), and their steady-state absorption and emission spectra measured. For comparison, the response of PIM-1 to non-explosive molecules such as benzene (BN) was also explored. Complementary electronic-structure calculations were used to predict absorption and emission spectra and to determine binding energies for the PIM-1-analyte complexes. The calculations agree well with experiment and reveal that association of nitroaromatic analyte molecules with PIM-1 alters the energy levels and the arrangements of frontier orbitals, indicating significant molecular interactions. Calculations show that the electronic properties and photo-excited electron transfer can be described by interaction with a single repeat unit of the polymer. The molecular binding, however, involves interaction with at least three repeat units, with the DNT or TNT molecule binding into a pocket in the contorted structure of the microporous polymer. Together, the experimental and theoretical results demonstrate that PIM-1 is a promising platform for selective nitroaromatic detection and provide molecular design principles that could improve sensitivity and selectivity in future sensor materials.

physics.chem-ph↗

arXiv2025

Optical Wireless Communications: Enabling the Next Generation Network of Networks

Optical wireless communication (OWC) is a promising technology anticipated to play a key role in the next-generation network of networks, especially as a complementary technology to traditional radio frequency communications, for enhancing networking capabilities beyond conventional terrestrial networks. OWC is already a mature technology with diverse usage scenarios, and can enable integrated applications via wireless access and backhaul networks, dynamic drone and satellite networks, underwater networks, inter- and intra-system interconnecting networks, and vehicular communication networks. Furthermore, novel and emerging technological opportunities such as photovoltaic cells, orbital angular momentum-based modulation, optical reconfigurable intelligent surfaces, organic light-emitting and photo diodes, and recent advances in ultraviolet communications can help enhance future OWC capabilities even further. Moreover, OWC networks can also support value-added services such as enhanced positioning and gesture recognition. Hence, OWC provides unique functionalities that can play a crucial role in building convergent and resilient future network of networks alongside radio frequency and optical fiber technologies.

eess.SP↗

arXiv2023

Achieving Bright Organic Light Emitting Field Effect Transistors with Sustained Efficiency through Hybrid Contact Design

Organic light emitting field effect transistors (OLEFETs) with bilayer structures have been widely studied due to their potential to integrate high-mobility organic transistors and efficient organic light emitting diodes. However, these devices face a major challenge of imbalance charge transport leading to severe efficiency roll-off at high brightness. Here, we propose a solution to this challenge by introducing a transparent organic/inorganic hybrid contact with specially designed electronic structures. Our design aims to steadily accumulate the electrons injected to the emissive polymer, allowing the light emitting interface to effectively capture more holes even when hole current increases. Our numerical simulations show that the capture efficiency of these steady electrons will dominate charge recombination and lead to a sustained external quantum efficiency of 0.23% over 3 orders of magnitude of brightness (4 to 7700 cd/m2) and current density (1.2 to 2700 mA/cm2) from -4 to -100 V. The same enhancement is retained even after increasing EQE to ~0.51%. The high and tunable brightness with stable efficiency offered by hybrid-contact OLEFETs make them ideal light emitting devices for various applications. These devices have the potential to revolutionize the field of organic electronics by overcoming the fundamental challenge of imbalance charge transport.

physics.app-ph↗

arXiv2023

Triple Halide Wide Bandgap Perovskites for Efficient Indoor Photovoltaics

Indoor photovoltaics are receiving tremendous attention due to the continuous development of the Internet of Things (IoT). Here we report a triple anion (TA) perovskite CH3NH3PbI2.6(BrCl)0.2 with a tailored bandgap suitable for maximizing indoor light harvesting compared to methyl ammonium lead iodide CH3NH3PbI3. The best-performing TA perovskite indoor-photovoltaic device achieved a steady-state power conversion efficiency (PCE) of 25.1% with an output power density of ~ 75 microW/cm2 under 1000 lux indoor illumination (0.3 mW/cm2 irradiance). This PCE is almost 40% higher than that of equivalent CH3NH3PbI3-based devices (PCE of 17.9%). Longer carrier lifetime, reduced density of trap states and improved crystalline quality were achieved by the triple anion alloying method. The decisive role of chlorine (Cl) in the better performance of TA-based indoor photovoltaic devices was further investigated by successively reducing the Cl content and correlating it with the corresponding photovoltaic device performance. Replacing the commonly used hole transporting layer of Spiro-MeOTAD with undoped P3HT was found to significantly reduce the current-voltage hysteresis under indoor lighting conditions. A graphene-coated textile fiber-based temperature sensor was successfully powered by the triple anion perovskite indoor photovoltaic devices. The results from the present study demonstrate a novel route to maximize the PCE of halide perovskite indoor photovoltaic devices and their potential for application in the IoT industry.

physics.app-ph↗

arXiv2019

Efficient indoor p-i-n hybrid perovskite solar cells using low temperature solution processed NiO as hole extraction layers

Hybrid perovskites have received tremendous attention due to their exceptional photovoltaic and optoelectronic properties. Among the two widely used perovskite solar cell device architectures of n-ip and p-i-n, the latter is interesting in terms of its simplicity of fabrication and lower energy input. However this structure mostly uses PEDOT:PSS as a hole transporting layer which can accelerate the perovskite solar cell degradation. Hence the development of stable, inorganic hole extraction layers (HEL), without compromising the simplicity of device fabrication is crucial in this fast-growing photovoltaic field. Here we demonstrate a low temperature (~100 oC) solution - processed and ultrathin (~ 6 nm) NiO nanoparticle thin films as an efficient HEL for CH3NH3PbI3 based perovskite solar cells. We measure a power conversion efficiency (PCE) of 13.3 % on rigid glass substrates and 8.5 % on flexible substrates. A comparison with PEDOT:PSS based MAPbI3 solar cells (PCE ~ 7.9 %) shows that NiO based solar cells have higher short circuit current density and improved open circuit voltage (1.03V). Apart from the photovoltaic performance under 1 Sun, the efficient hole extraction property of NiO is demonstrated for indoor lighting as well with a PCE of 23.0 % for NiO based CH3NH3PbI2.9Cl0.1 p-i-n solar cells under compact fluorescent lighting. Compared to the perovskite solar cells fabricated on PEDOT:PSS HEL, better shelf-life stability is observed for perovskite solar cells fabricated on NiO HEL. Detailed microstructural and photophysical investigations imply uniform morphology, lower recombination losses, and improved charge transfer properties for CH3NH3PbI3 grown on NiO HEL.

physics.app-ph↗

arXiv2018

Influence of Perfluorinated Ionomer in PEDOT:PSS on the Rectification and Degradation of Organic Photovoltaic Cells

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is widely used to build optoelectronic devices. However, as a hygroscopic water-based acidic material, it brings major concerns for stability and degradation, resulting in an intense effort to replace it in organic photovoltaic (OPV) devices. In this work, we focus on the perfluorinated ionomer (PFI) polymeric additive to PEDOT:PSS. We demonstrate that it can reduce the relative amplitude of OPV device burn-in, and find two distinct regimes of influence. At low concentrations there is a subtle effect on wetting and work function, for instance, with a detrimental impact on the device characteristics, and above a threshold it changes the electronic and device properties. The abrupt threshold in the conducting polymer occurs for PFI concentrations greater than or equal to the PSS concentration and was revealed by monitoring variations in transmission, topography, work-function, wettability and OPV device characteristics. Below this PFI concentration threshold, the power conversion efficiency (PCE) of OPVs based on poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) are impaired largely by low fill-factors due to poor charge extraction. Above the PFI concentration threshold, we recover the PCE before it is improved beyond the pristine PEDOT:PSS layer based OPV devices. Supplementary to the performance enhancement, PFI improves OPV device stability and lifetime. Our degradation study leads to the conclusion that PFI prevents water from diffusing to and from the hygrosopic PEDOT:PSS layer, which slows down the deterioration of the PEDOT:PSS layer and the aluminum electrode. These findings reveal mechanisms and opportunities that should be taken into consideration when developing components to inhibit OPV degradation.

physics.app-ph↗