Tyrian purple : an ancient natural dye for cross-conjugated n-type charge transport

Herein, we present two novel organic semiconducting polymers synthesised from an ancient dye. By employing cross-conjugation within the polymer backbone as a synthetic strategy, we are able to engineer optical gaps such that the novel materials absorb over the entire visible spectrum. The cross-conjugated polymers exhibited relatively high n-type charge transport performance in organic field-effect transistors, a rare characteristic for this type of polymer. Quantum chemical calculations provide insight into this behaviour, suggesting that, whilst conjugation along the HOMO is indeed inhibited via molecular design, these materials possess highly delocalized LUMOs, facilitating high n-type charge transport

Copper (I) selenocyanate (CuSeCN) as a novel hole-transport layer for transistors, organic solar cells, and light-emitting diodes

The synthesis and characterization of copper (I) selenocyanate (CuSeCN) and its application as a solution-processable hole-transport layer (HTL) material in transistors, organic light-emitting diodes, and solar cells are reported. Density-functional theory calculations combined with X-ray photoelectron spectroscopy are used to elucidate the electronic band structure, density of states, and microstructure of CuSeCN. Solution-processed layers are found to be nanocrystalline and optically transparent ( > 94%), due to the large bandgap of ≥3.1 eV, with a valence band maximum located at -5.1 eV. Hole-transport analysis performed using field-effect measurements confirms the p-type character of CuSeCN yielding a hole mobility of 0.002 cm 2 V -1 s -1 . When CuSeCN is incorporated as the HTL material in organic light-emitting diodes and organic solar cells, the resulting devices exhibit comparable or improved performance to control devices based on commercially available poly(3,4-ethylenedioxythiophene):polystyrene sulfonate as the HTL. This is the first report on the semiconducting character of CuSeCN and it highlights the tremendous potential for further developments in the area of metal pseudohalides

Taming copper(I) cyanate and selenocyanate with N-heterocyclic carbenes

The synthesis of N-heterocyclic carbene (NHC) adducts of copper(I) cyanate and copper(I) selenocyanate has been successfully achieved via the reaction of [Cu(NHC)Cl] with silver(I) cyanate and potassium selenocyanate respectively. Three copper(I) cyanate complexes [Cu(IXy)(NCO)] (1), [Cu(IPr)(NCO)] (2) and [Cu(SIPr)(NCO)] (3) [IXy = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene, IPr = 1,3- bis(2,6-diisopropylphenyl)imidazol-2-ylidene, SIPr = 1,3-bis(2,6- diisopropylphenyl)imidazolin-2-ylidene] have been prepared and fully characterised. The X-ray crystal structures reveal the three complexes to be monomeric species in which the cyanate ligand is end-on, N-bound. These complexes, represent the first examples of monomeric copper(I) cyanate complexes. In addition, the copper(I) selenocyanate species [Cu(IPr)(NCSe)]2 (4) was prepared and fully characterised. The X-ray crystal structure reveals that a centrosymmetric dimer is formed with bridging selenocyanate ligands bound through both N and Se. This is in contrast to the monomeric structure observed in the previously reported and related complex [Cu(IPr)(NCS)]. Complex 4 represents a rare example of a stable dimeric adduct of copper(I) selenocyanate

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

Electronic Properties of Copper(I) Thiocyanate (CuSCN)

With the emerging applications of copper(I) thiocyanate (CuSCN) as a transparent and solution-processable hole-transporting semiconductor in numerous opto/electronic devices, fundamental studies that cast light on the charge transport physics are essential as they provide insights critical for further materials and devices performance advancement. The aim of this article is to provide a comprehensive and up-to-date report of the electronic properties of CuSCN with key emphasis on the structure–property relationship. The article is divided into four parts. In the first section, recent works on density functional theory calculations of the electronic band structure of hexagonal β-CuSCN are reviewed. Following this, various defects that may contribute to the conductivity of CuSCN are discussed, and newly predicted phases characterized by layered 2-dimensional-like structures are highlighted. Finally, a summary of recent studies on the band-tail states and hole transport mechanisms in solution-deposited, polycrystalline CuSCN layers is presented

Copper(I) Thiocyanate (CuSCN) Hole-Transport Layers Processed from Aqueous Precursor Solutions and Their Application in Thin-Film Transistors and Highly Efficient Organic and Organometal Halide Perovskite Solar Cells

This study reports the development of copper(I) thiocyanate (CuSCN) hole-transport layers (HTLs) processed from aqueous ammonia as a novel alternative to conventional n-alkyl sulfide solvents. Wide bandgap (3.4–3.9 eV) and ultrathin (3–5 nm) layers of CuSCN are formed when the aqueous CuSCN–ammine complex solution is spin-cast in air and annealed at 100 °C. X-ray photoelectron spectroscopy confirms the high compositional purity of the formed CuSCN layers, while the high-resolution valence band spectra agree with first-principles calculations. Study of the hole-transport properties using field-effect transistor measurements reveals that the aqueous-processed CuSCN layers exhibit a fivefold higher hole mobility than films processed from diethyl sulfide solutions with the maximum values approaching 0.1 cm2 V−1 s−1. A further interesting characteristic is the low surface roughness of the resulting CuSCN layers, which in the case of solar cells helps to planarize the indium tin oxide anode. Organic bulk heterojunction and planar organometal halide perovskite solar cells based on aqueous-processed CuSCN HTLs yield power conversion efficiency of 10.7% and 17.5%, respectively. Importantly, aqueous-processed CuSCN-based cells consistently outperform devices based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate HTLs. This is the first report on CuSCN films and devices processed via an aqueous-based synthetic route that is compatible with high-throughput manufacturing and paves the way for further developments

Perovskite solar cells: An integrated hybrid lifecycle assessment and review in comparison with other photovoltaic technologies

Solar cells are considered as one of the prominent sources of renewable energy suitable for large-scale adoption in a carbon-constrained world and can contribute to reduced reliance on energy imports, whilst improving the security of energy supply. A new arrival in the family of solar cells technologies is the organic-inorganic halide perovskite. The major thrust for endorsing these new solar cells pertains to their potential as an economically and environmentally viable option to traditional silicon-based technology. To verify this assertion, this paper presents a critical review of some existing photovoltaic (PV) technologies in comparison with perovskite-structured solar cells (PSCs), including material and performance parameters, production processes and manufacturing complexity, economics, key technological challenges for further developments and current research efforts. At present, there is limited environmental assessment of PSCs and consequently, a methodologically robust and environmentally expansive lifecycle supply chain assessment of two types of PSC modules A and B is also undertaken within the context of other PV technologies, to assess their potential for environmentally friendly innovation in the energy sector. Module A is based on MAPbX3 perovskite structure while module B is based on CsFAPbX3 with improved stability, reproducibility and high performance efficiency. The main outcomes, presented along with sensitivity analysis, show that PSCs offer more environmentally friendly and sustainable option, with the least energy payback period, as compared to other PV technologies. The review and analysis presented provide valuable insight and guidance in identifying pathways and windows of opportunity for future PV designs towards cleaner and sustainable energy production

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