Assessing the suitability of copper thiocyanate as a hole-transport layer in inverted CsSnI3 perovskite photovoltaics

We report the fndings of a study into the suitability of copper (I) thiocyanate (CuSCN) as a hole-transport layer in inverted photovoltaic (PV) devices based on the black gamma phase (B-γ) of CsSnl3 perovskite. Remarkably, when B-γ-CsSnI3 perovskite is deposited from a dimethylformamide solution onto a 180–190nm thick CuSCN flm supported on an indium-tin oxide (ITO) electrode, the CuSCN layer is completely displaced leaving a perovskite layer with high uniformity and coverage of the underlying ITO electrode. This fnding is confrmed by detailed analysis of the thickness and composition of the film that remains after perovskite deposition, together with photovoltaic device studies. The results of this study show that, whilst CuSCN has proved to be an excellent hole-extraction layer for high performance lead-perovskite and organic photovoltaics, it is unsuitable as a hole-transport layer in inverted B-γCsSnI3 perovskite photovoltaics processed from solution

Copper pseudohalides as solution-processable hole-transport materials for opto/electronic applications

This thesis presents the development of novel copper pseudohalide hole-transport layers (HTLs) for thin-film transistors (TFTs), organic photovoltaic (OPV) cells, perovskite solar cells (PSCs), and organic light-emitting diodes (OLEDs). Their impact on device performance is assessed relative to two reference HTLs: a conventional polymer HTL, and copper(I) thiocyanate (CuSCN) deposited via an n-alkyl sulphide solvent (diethyl sulphide, DES). The first experimental chapter demonstrates aqueous ammonia (NH3 (aq)) as a novel processing solvent for CuSCN, which produces HTLs with greatly enhanced electronic and structural properties. CuSCN/NH3 HTLs exhibit exceptional anode planarisation properties and mean field-effect hole mobility (µ) of 0.05 cm2 V-1 s-1. OPV cells and PSCs employing a CuSCN/NH3 HTL consistently outperform devices utilising a reference HTL by achieving maximum power conversion efficiency of 10.7% (OPV) and 17.5% (PSC). Next, a fluorinated fullerene (C60F48) is utilised as a p-dopant for CuSCN/DES. Analysis of material and device characterisation data reveal strong evidence of a successful p-doping process. Mean µ of 0.12 cm2 V-1 s-1 is measured in TFTs based on CuSCN:C60F48 (0.5 mol%), which is a twelvefold increase relative to pristine CuSCN. Additional advantages include an order of magnitude reduction in contact resistance, a dramatic increase in bias stability, and a change in the dominant hole-transport mechanism from trap limited conduction to percolation conduction. Optimised CuSCN:C60F48 HTLs also outperform reference HTLs in OPV applications; substantial increases in fill factor and device yield are observed. Finally, the third experimental chapter reports on a novel wide-bandgap (≥3.1 eV) p-type semiconductor, copper(I) selenocyanate (CuSeCN). Its electronic, structural and optical properties are predicted using density functional theory calculations and verified using numerous experimental techniques. CuSeCN/DES layers annealed at 140 ˚C exhibit excellent performance in TFTs, OPV cells, and OLEDs. Hence, this thesis demonstrates the tremendous potential of copper pseudohalides as universal HTLs for opto/electronics.Open Acces

Laser-induced grating spectroscopy in non-uniform temperature fields and flames

The application of Laser-Induced Grating Spectroscopy (LIGS) to thermometry of temperature-controlled ethylene flows and an ethylene-air flame from a Gülder burner is studied. A model for simulating the effect of contributions from regions of different temperature within the LIGS probe volume is developed for comparison with experimental data. The model includes a weighted sum of contributions from regions at a single temperature to the total signal intensity. An appropriate experimental set-up is constructed for this study, with careful consideration given to the dimensions of the probe volume. Temperature measurements are made in a dual flow of ethylene, where the probe volume contains two distinct temperature regions: one from an unheated flow and the second from a temperature-controlled hot flow. The model is shown to correspond well with experimental data; the presence of two discrete contributions, 293 ± 2 K and 310 ± 2K (0.6 – 0.7% precision), is identified in the LIGS signal from the cooler region. LIGS signals are recorded at several spatial positions in the lower region of a flame with fixed stoichiometry. Signals measured in the 0.0 – 5.0 mm height above burner (HAB) range and the 0.0 – 3.5 mm radial position range are analysed using MATLAB; temperature information is extracted with precisions of 0.9 – 4.4%. The OH* distribution in the flame is recorded during a chemiluminescence experiment to identify the location of the reaction zone. The model is used to demonstrate that derived temperatures are the spatial average of a continuous temperature gradient within the probe volume. The suitability of LIGS for thermometry in environments with unknown temperature gradients is thus verified. Comparisons are made between the flame measurements and ethylene flow data; simple changes to improve the model are proposed. Strong non-oscillatory decay features in the LIGS signal, indicative of the laser heating of soot, are reported at HAB 20.0 – 50.0 mm; relevant implications are discussed.</p

Laser-induced grating spectroscopy in non-uniform temperature fields and flames

The application of Laser-Induced Grating Spectroscopy (LIGS) to thermometry of temperature-controlled ethylene flows and an ethylene-air flame from a Gülder burner is studied. A model for simulating the effect of contributions from regions of different temperature within the LIGS probe volume is developed for comparison with experimental data. The model includes a weighted sum of contributions from regions at a single temperature to the total signal intensity. An appropriate experimental set-up is constructed for this study, with careful consideration given to the dimensions of the probe volume. Temperature measurements are made in a dual flow of ethylene, where the probe volume contains two distinct temperature regions: one from an unheated flow and the second from a temperature-controlled hot flow. The model is shown to correspond well with experimental data; the presence of two discrete contributions, 293 ± 2 K and 310 ± 2K (0.6 – 0.7% precision), is identified in the LIGS signal from the cooler region. LIGS signals are recorded at several spatial positions in the lower region of a flame with fixed stoichiometry. Signals measured in the 0.0 – 5.0 mm height above burner (HAB) range and the 0.0 – 3.5 mm radial position range are analysed using MATLAB; temperature information is extracted with precisions of 0.9 – 4.4%. The OH* distribution in the flame is recorded during a chemiluminescence experiment to identify the location of the reaction zone. The model is used to demonstrate that derived temperatures are the spatial average of a continuous temperature gradient within the probe volume. The suitability of LIGS for thermometry in environments with unknown temperature gradients is thus verified. Comparisons are made between the flame measurements and ethylene flow data; simple changes to improve the model are proposed. Strong non-oscillatory decay features in the LIGS signal, indicative of the laser heating of soot, are reported at HAB 20.0 – 50.0 mm; relevant implications are discussed.This thesis is not currently available in ORA

Radiofrequency Schottky diodes based on p-doped copper(I) thiocyanate (CuSCN)

Schottky diodes based on inexpensive materials that can be processed using simple manufacturing methods are of particular importance for the next generation of flexible electronics. Although a number of high-frequency n-type diodes and rectifiers have been demonstrated, the progress with p-type diodes is lagging behind, mainly due to the intrinsically low conductivities of existing p-type semiconducting materials that are compatible with low-temperature, flexible, substrate-friendly processes. Herein, we report on CuSCN Schottky diodes, where the semiconductor is processed from solution, featuring coplanar Al–Au nanogap electrodes (&lt;15 nm), patterned via adhesion lithography. The abundant CuSCN material is doped with the molecular p-type dopant fluorofullerene C60F48 to improve the diode’s operating characteristics. Rectifier circuits fabricated with the doped CuSCN/C60F48 diodes exhibit a 30-fold increase in the cutoff frequency as compared to pristine CuSCN diodes (from 140 kHz to 4 MHz), while they are able to deliver output voltages of &gt;100 mV for a VIN = ±5 V at the commercially relevant frequency of 13.56 MHz. The enhanced diode and circuit performance is attributed to the improved charge transport across CuSCN induced by C60F48. The ensuing diode technology can be used in flexible complementary circuits targeting low-energy-budget applications for the emerging internet of things device ecosystem