Publications
Results
- Showing results for:
- Reset all filters
Search results
-
Journal articleLee J, Lee J-H, Yao H, et al., 2020,
Efficient and photostable ternary organic solar cells with a narrow band gap non-fullerene acceptor and fullerene additive
, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 8, Pages: 6682-6691, ISSN: 2050-7488- Author Web Link
- Cite
- Citations: 24
-
Journal articleBack H, Kim G, Kim H, et al., 2020,
Highly stable inverted methylammonium lead tri-iodide perovskite solar cells achieved by surface re-crystallization
, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 13, Pages: 840-847, ISSN: 1754-5692- Author Web Link
- Cite
- Citations: 36
-
Journal articleSpitler MT, Modestino MA, Deutsch TG, et al., 2020,
Practical challenges in the development of photoelectrochemical solar fuels production
, SUSTAINABLE ENERGY & FUELS, Vol: 4, Pages: 985-995, ISSN: 2398-4902- Author Web Link
- Cite
- Citations: 35
-
Journal articleLin C-T, Lee J, Kim J, et al., 2020,
Origin of open-circuit voltage enhancements in planar Perovskite solar cells induced by addition of bulky organic cations
, Advanced Functional Materials, Vol: 30, ISSN: 1616-301XThe origin of performance enhancements in p‐i‐n perovskite solar cells (PSCs) when incorporating low concentrations of the bulky cation 1‐naphthylmethylamine (NMA) are discussed. A 0.25 vol % addition of NMA increases the open circuit voltage (Voc) of methylammonium lead iodide (MAPbI3) PSCs from 1.06 to 1.16 V and their power conversion efficiency (PCE) from 18.7% to 20.1%. X‐ray photoelectron spectroscopy and low energy ion scattering data show NMA is located at grain surfaces, not the bulk. Scanning electron microscopy shows combining NMA addition with solvent assisted annealing creates large grains that span the active layer. Steady state and transient photoluminescence data show NMA suppresses non‐radiative recombination resulting from charge trapping, consistent with passivation of grain surfaces. Increasing the NMA concentration reduces device short‐circuit current density and PCE, also suppressing photoluminescence quenching at charge transport layers. Both Voc and PCE enhancements are observed when bulky cations (phenyl(ethyl/methyl)ammonium) are incorporated, but not smaller cations (Cs/MA)—indicating size is a key parameter. Finally, it demonstrates that NMA also enhances mixed iodide/bromide wide bandgap PSCs (Voc of 1.22 V with a 1.68 eV bandgap). The results demonstrate a facile approach to maximizing Voc and provide insights into morphological control and charge carrier dynamics induced by bulky cations in PSCs.
-
Journal articleCorby S, Francàs L, Kafizas A, et al., 2020,
Determining the role of oxygen vacancies in the photoelectrocatalytic performance of WO3 for water oxidation
, Chemical Science, Vol: 11, Pages: 2907-2914, ISSN: 2041-6520Oxygen vacancies are common to most metal oxides, whether intentionally incorporated or otherwise, and the study of these defects is of increasing interest for solar water splitting. In this work, we examine nanostructured WO3 photoanodes of varying oxygen content to determine how the concentration of bulk oxygen-vacancy states affects the photocatalytic performance for water oxidation. Using transient optical spectroscopy, we follow the charge carrier recombination kinetics in these samples, from picoseconds to seconds, and examine how differing oxygen vacancy concentrations impact upon these kinetics. We find that samples with an intermediate concentration of vacancies (∼2% of oxygen atoms) afford the greatest photoinduced charge carrier densities, and the slowest recombination kinetics across all timescales studied. This increased yield of photogenerated charges correlates with improved photocurrent densities under simulated sunlight, with both greater and lesser oxygen vacancy concentrations resulting in enhanced recombination losses and poorer J–V performances. Our conclusion, that an optimal – neither too high nor too low – concentration of oxygen vacancies is required for optimum photoelectrochemical performance, is discussed in terms of the competing beneficial and detrimental impact these defects have on charge separation and transport, as well as the implications held for other highly doped materials for photoelectrochemical water oxidation.
-
Journal articleHamid Z, Wadsworth A, Rezasoltani E, et al., 2020,
Influence of Polymer Aggregation and Liquid Immiscibility on Morphology Tuning by Varying Composition in PffBT4T-2DT/Nonfullerene Organic Solar Cells
, ADVANCED ENERGY MATERIALS, Vol: 10, ISSN: 1614-6832 -
Journal articleFrancas L, Corby S, Selim S, et al., 2020,
Spectroelectrochemical study of water oxidation on nickel and iron oxyhydroxide electrocatalysts (vol 10, 5208, 2019)
, NATURE COMMUNICATIONS, Vol: 11, ISSN: 2041-1723 -
Journal articleHong DP, Jain SM, Li M, et al., 2020,
All-Rounder Low-Cost Dopant-Free D-A-D Hole-Transporting Materials for Efficient Indoor and Outdoor Performance of Perovskite Solar Cells
, ADVANCED ELECTRONIC MATERIALS, Vol: 6, ISSN: 2199-160X- Author Web Link
- Cite
- Citations: 45
-
BookDurrant J, 2020,
Foreword
, ISBN: 9780128178362 -
Journal articleAchilleos DS, Yang W, Kasap H, et al., 2020,
Solar Reforming of Biomass with Homogeneous Carbon Dots
, Angewandte Chemie, ISSN: 0044-8249© 2020 The Authors. Published by Wiley-VCH GmbH A sunlight-powered process is reported that employs carbon dots (CDs) as light absorbers for the conversion of lignocellulose into sustainable H2 fuel and organics. This photocatalytic system operates in pure and untreated sea water at benign pH (2–8) and ambient temperature and pressure. The CDs can be produced in a scalable synthesis directly from biomass itself and their solubility allows for good interactions with the insoluble biomass substrates. They also display excellent photophysical properties with a high fraction of long-lived charge carriers and the availability of a reductive and an oxidative quenching pathway. The presented CD-based biomass photoconversion system opens new avenues for sustainable, practical, and renewable fuel production through biomass valorization.
-
Journal articleMesa Zamora C, Francas Forcada L, Yang KR, et al., 2020,
Multihole water oxidation catalysis on hematite photoanodes revealed by operando spectroelectrochemistry and DFT
, Nature Chemistry, Vol: 12, Pages: 82-89, ISSN: 1755-4330Water oxidation is the key kinetic bottle neck of photoelectrochemical devices for fuel synthesis. Despite advances in the identification of intermediates, elucidating the catalytic mechanism of this multi-redox reactionon metal-oxidephotoanodes remains a significant experimental and theoretical challenge. Here we report an experimental analysis of water oxidation kinetics on four widely studied metal oxides, focusing particularly upon hematite.We observe that hematite is able toaccess a reaction mechanism third order in surface hole density, assigned to equilibration between three surface holes and M(OH)-O-M(OH) sites. This reaction exhibits a remarkably low activation energy (Ea~ 60 meV). Density functional theory is employedto determine the energetics of charge accumulation and O-O bond formation on a modelhematite 110 surface. The proposed mechanism shows parallels with the function of oxygen evolving complex of photosystem II,and provides new insights to the mechanism of heterogeneous water oxidation on a metal oxide surface.
-
Journal articleDaboczi M, Hamilton I, Xu S, et al., 2019,
Origin of Open-Circuit Voltage Losses in Perovskite Solar Cells Investigated by Surface Photovoltage Measurement
, ACS Applied Materials & Interfaces, Vol: 11, Pages: 46808-46817, ISSN: 1944-8244 -
Journal articleSelim S, Pastor E, García-Tecedor M, et al., 2019,
Impact of oxygen vacancy occupancy on charge carrier dynamics in BiVO4 photoanodes
, Journal of the American Chemical Society, Vol: 141, Pages: 18791-18798, ISSN: 0002-7863Oxygen vacancies are ubiquitous in metal oxides and critical to performance, yet the impact of these states upon charge carrier dynamics important for photoelectrochemical and photocatalytic applications, remains contentious and poorly understood. A key challenge is the unambiguous identification of spectroscopic fingerprints which can be used to track their function. Herein, we employ five complementary techniques to modulate the electronic occupancy of states associated with oxygen vacancies in situ in BiVO4 photoanodes, allowing us to identify a spectral signature for the ionisation of these states. We obtain an activation energy of ̴ 0.2 eV for this ionisation process, with thermally activated electron de-trapping from these states determining the kinetics of electron extraction, consistent with improved photoelectrochemical performance at higher temperatures. Bulk, un-ionised states however, function as deep hole traps, with such trapped holes being energetically unable to drive water oxidation. These observations help address recent controversies in the literature over oxygen vacancy function, providing new insights into their impact upon photoelectrochemical performance.
-
Journal articleAmbroz F, Xu W, Gadipelli S, et al., 2019,
Room Temperature Synthesis of Phosphine-Capped Lead Bromide Perovskite Nanocrystals without Coordinating Solvents
, PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Vol: 37, ISSN: 0934-0866 -
Journal articleFrancàs L, Corby S, Selim S, et al., 2019,
Spectroelectrochemical study of water oxidation on nickel and iron oxyhydroxide electrocatalysts
, Nature Communications, Vol: 10, ISSN: 2041-1723Ni/Fe oxyhydroxides are the best performing Earth-abundant electrocatalysts for water oxidation. However, the origin of their remarkable performance is not well understood. Herein, we employ spectroelectrochemical techniques to analyse the kinetics of water oxidation on a series of Ni/Fe oxyhydroxide films: FeOOH, FeOOHNiOOH, and Ni(Fe)OOH (5% Fe). The concentrations and reaction rates of the oxidised states accumulated during catalysis are determined. Ni(Fe)OOH is found to exhibit the fastest reaction kinetics but accumulates fewer states, resulting in a similar performance to FeOOHNiOOH. The later catalytic onset in FeOOH is attributed to an anodic shift in the accumulation of oxidised states. Rate law analyses reveal that the rate limiting step for each catalyst involves the accumulation of four oxidised states, Ni-centred for Ni(Fe)OOH but Fe-centred for FeOOH and FeOOHNiOOH. We conclude by highlighting the importance of equilibria between these accumulated species and reactive intermediates in determining the activity of these materials.
-
Journal articleWu J, Luke J, Lee HKH, et al., 2019,
Tail state limited photocurrent collection of thick photoactive layers in organic solar cells
, Nature Communications, Vol: 10, ISSN: 2041-1723Weanalyseorganic solar cells with four differentphotoactive blends exhibiting differing dependencies ofshort-circuit current upon photoactive layer thickness.These blends and devices are analysedbytransient optoelectronic techniques ofcarrier kinetics and densities, airphotoemission spectroscopyof material energetics, Kelvin probe measurements of work function, Mott-Schottky analyses of apparent doping density and by device modelling. We concludethat,for the device series studied, the photocurrent losswith thick active layersis primarilyassociatedwith the accumulation of photo-generated charge carriers in intra-bandgap tail states.This charge accumulation screens the device internal electricalfield, preventing efficient charge collection. Purification of one studied donor polymer is observed to reduce tail statedistribution anddensity and increase the maximal photoactive thickness forefficient operation. Ourwork suggests that selectingorganic photoactive layerswith a narrow distribution of tail states isa keyrequirement for the fabrication of efficient, high photocurrent, thick organic solar cells.
-
Journal articleJia D, Chen J, Zheng S, et al., 2019,
Highly Stabilized Quantum Dot Ink for Efficient Infrared Light Absorbing Solar Cells
, Advanced Energy Materials, Vol: 9, Pages: 1902809-1902809, ISSN: 1614-6832 -
Journal articleTian L, Törndahl T, Lin J, et al., 2019,
Mechanistic Insights into Solid-State p-Type Dye-Sensitized Solar Cells
, The Journal of Physical Chemistry C, Vol: 123, Pages: 26151-26160, ISSN: 1932-7447 -
Journal articleCorby S, Francàs L, Kafizas A, et al., 2019,
Determining the Role of Oxygen Vacancies in the Photocatalytic Performance of WO3 for Water Oxidation
<jats:p>Oxygen vacancies are common to most metal oxides, whether intentionally incorporated or otherwise, and the study of these defects is of increasing interest for solar water splitting. In this work, we examine nanostructured WO<jats:sub>3</jats:sub> photoanodes of varying oxygen content to determine how the concentration of bulk oxygen-vacancy states affects the photocatalytic performance for water oxidation. Using transient optical spectroscopy, we follow the charge carrier recombination kinetics in these samples, from picoseconds to seconds, and examine how differing oxygen vacancy concentrations impact upon these kinetics. We find that samples with an intermediate concentration of vacancies (~2% of oxygen atoms) afford the greatest photoinduced charge carrier densities, and the slowest recombination kinetics across all timescales studied. This increased yield of photogenerated charges correlates with improved photocurrent densities under simulated sunlight, with both greater and lesser oxygen vacancy concentrations resulting in enhanced recombination losses and poorer J-V performances. Our conclusion, that an optimal – neither too high nor too low – concentration of oxygen vacancies is required for optimum photoelectrochemical performance, is discussed in terms of the impact of these defects on charge separation and transport, as well as the implications held for other highly doped materials for photoelectrochemical water oxidation.</jats:p>
-
Journal articleLuo H, Papaioannou N, Salvadori E, et al., 2019,
Manipulating the Optical Properties of Carbon Dots by Fine-Tuning their Structural Features
, CHEMSUSCHEM, Vol: 12, Pages: 4432-4441, ISSN: 1864-5631- Author Web Link
- Cite
- Citations: 6
-
Journal articleHe Q, Shahid M, Wu J, et al., 2019,
Fused Cyclopentadithienothiophene acceptor enables ultrahigh short‐circuit current and high efficiency >11% in as‐cast organic solar cells
, Advanced Functional Materials, Vol: 29, Pages: 1-7, ISSN: 1616-301XA new method to synthesize an electron‐rich building block cyclopentadithienothiophene (9H‐thieno‐[3,2‐b]thieno[2″,3″:4′,5′]thieno[2′,3′:3,4]cyclopenta[1,2‐d]thiophene, CDTT) via a facile aromatic extension strategy is reported. By combining CDTT with 1,1‐dicyanomethylene‐3‐indanone endgroups, a promising nonfullerene small molecule acceptor (CDTTIC) is prepared. As‐cast, single‐junction nonfullerene organic solar cells based on PFBDB‐T: CDTTIC blends exhibit very high short‐circuit currents up to 26.2 mA cm−2 in combination with power conversion efficiencies over 11% without any additional processing treatments. The high photocurrent results from the near‐infrared absorption of the CDTTIC acceptor and the well‐intermixed blend morphology of polymer donor PFBDB‐T and CDTTIC. This work demonstrates a useful fused ring extension strategy and promising solar cell results, indicating the great potential of the CDTT derivatives as electron‐rich building blocks for constructing high‐performance small molecule acceptors in organic solar cells.
-
Journal articleMacdonald TJ, Batmunkh M, Lin C-T, et al., 2019,
Origin of performance enhancement in TiO2-carbon nanotube composite perovskite solar cells
, Small Methods, Vol: 3, Pages: 1-10, ISSN: 2366-9608Carbon nanotubes are shown to be beneficial additives to perovskite solar cells, and the inclusion of such nanomaterials will continue to play a crucial role in the push toward developing efficient and stable device architectures. Herein, titanium dioxide/carbon nanotube composite perovskite solar cells are fabricated, and device performance parameters are correlated with spectroscopic signatures of the materials to understand the origin of performance enhancement. By probing the charge carrier dynamics with photoluminescence and femtosecond transient absorption spectroscopy, the results indicate that charge transfer is not improved by the presence of the carbon nanotubes. Instead, carbon nanotubes are shown to passivate the electronic defect states within the titanium dioxide, which can lead to stronger radiative recombination in the titanium dioxide/carbon nanotube films. The defect passivation allows the perovskite solar cells made using an optimized titanium dioxide/carbon nanotube composite to achieve a peak power conversion efficiency of 20.4% (19% stabilized), which is one of the highest values reported for perovskite solar cells not incorporating a mixed cation light absorbing layer. The results discuss new fundamental understandings for the role of carbon nanomaterials in perovskite solar cells and present a significant step forward in advancing the field of high‐performance photovoltaics.
-
Journal articleSung MJ, Hong J, Cha H, et al., 2019,
Acene-Modified Small-Molecule Donors for Organic Photovoltaics
, Chemistry - A European Journal, Vol: 25, ISSN: 0947-6539Invited for the cover of this issue is the group of Tae Kyu An at the Korea National University of Transportation, Soon-Ki Kwon and Yun-Hi Kim at the Gyeongsang National University. The image depicts organic photovoltaics, in which fused acene cores have been used to modulate the conjugation lengths and the bulk heterojunction morphologies. Read the full text of the article at 10.1002/chem.201902177.
-
Journal articleCorby S, Pastor E, Dong Y, et al., 2019,
Charge separation, band-bending, and recombination in WO3 photoanodes
, Journal of Physical Chemistry Letters, Vol: 10, Pages: 5395-5401, ISSN: 1948-7185In metal oxide-based photoelectrochemical devices, the spatial separation of photogenerated electrons and holes is typically attributed to band-bending at the oxide/electrolyte interface. However, direct evidence of such band-bending impacting upon charge carrier lifetimes has been very limited to date. Herein we use ultrafast spectroscopy to track the rapid relaxation of holes in the space-charge layer and their recombination with trapped electrons in WO3 photoanodes. We observe that applied bias can significantly increase carrier lifetimes on all time scales from picoseconds to seconds and attribute this to enhanced band-bending correlated with changes in oxygen vacancy state occupancy. We show that analogous enhancements in carrier lifetimes can be obtained by changes in electrolyte composition, even in the absence of applied bias, highlighting routes to improve photoconversion yields/performance, through changes in band-bending. This study thus demonstrates the direct connection between carrier lifetime enhancement, increased band-bending, and oxygen vacancy defect state occupancy.
-
Journal articleBakulin A, Pastor E, Park J-S, et al., 2019,
In situ observation of picosecond polaron self-localisation in α-Fe2O3 photoelectrochemical cells
, Nature Communications, Vol: 10, ISSN: 2041-1723Hematite (α-Fe2O3) is the most studied artificial oxygen-evolving photo-anode and yet its efficiency limitations and their origin remain unknown. A sub-picosecond reorganisation of the hematite structure has been proposed as the mechanism which dictates carrier lifetimes, energetics and the ultimate conversion yields. However, the importance of this reorganisation for actual device performance is unclear. Here we report an in situ observation of charge carrier self-localisation in a hematite device, and demonstrate that this process affects recombination losses in photoelectrochemical cells. We apply an ultrafast, device-based optical-control method to resolve the subpicosecond formation of small polarons and estimate their reorganisation energy to be ~0.5 eV. Coherent oscillations in the photocurrent signals indicate that polaron formation may be coupled to specific phonon modes (<100 cm-1). Our results bring together spectroscopic and device characterisation approaches to reveal new photophysics of broadly-studied hematite devices.
-
Journal articleDurrant J, 2019,
(Keynote) Transient Absorption Studies of Charge Carrier Dynamics in Photocatalysts and Photoelectrodes for Solar Driven Water Splitting
, ECS Meeting Abstracts, Vol: MA2019-02, Pages: 1915-1915<jats:p> In my talk I will focus on the underlying charge carrier dynamics which determine the efficiency of solar driven water splitting by a range of photoelectrodes and photocatalyst suspensions, including metal oxide photoanodes and carbon nitride and polymer based photocatalysts. The key kinetic challenge in these materials is to match the lifetimes of photogenerated carriers with the timescales of water oxidation / reduction catalysis. I will discuss our studies addressing this kinetic challenge on timescales from picoseconds to seconds. Key factors which will be considered will include the relevant timescales of bulk carrier recombination, and how these differ between materials, the timescales of catalysis, the role of space charge layers and junctions in separating charges, the impact of charge trapping on charge carrier lifetimes and reactivity, and the impact of polaron formation. </jats:p>
-
Journal articleWang Y, Vogel A, Sachs M, et al., 2019,
Current understanding and challenges of solar-driven hydrogen generation using polymeric photocatalysts
, Nature Energy, Vol: 4, Pages: 746-760, ISSN: 2058-7546The use of hydrogen as a fuel, when generated from water using semiconductor photocatalysts and driven by sunlight, is a sustainable alternative to fossil fuels. Polymeric photocatalysts are based on Earth-abundant elements and have the advantage over their inorganic counterparts in that their electronic properties are easily tuneable through molecular engineering. Polymeric photocatalysts have developed rapidly over the past decade, resulting in the discovery of many active materials. However, our understanding of the key properties underlying their photoinitiated redox processes has not kept pace, and this impedes further progress to generate cost-competitive technologies. Here, we discuss state-of-the-art polymeric photocatalysts and our microscopic understanding of their activities. We conclude with a discussion of five outstanding challenges in this field: non-standardized reporting of activities, limited photochemical stability, insufficient knowledge of reaction mechanisms, balancing charge carrier lifetimes with catalysis timescales and the use of unsustainable sacrificial reagents.
-
Journal articlePont S, Osella S, Smith A, et al., 2019,
Evidence for strong and weak phenyl-C61-butyric acid methyl ester photodimer populations in organic solar cells
, Chemistry of Materials, Vol: 31, Pages: 6076-6083, ISSN: 0897-4756In polymer/fullerene organic solar cells, the photochemical dimerization of phenyl-C61-butyric acid methyl ester (PCBM) was reported to have either a beneficial or a detrimental effect on device performance and stability. In this work, we investigate the behavior of such dimers by measuring the temperature dependence of the kinetics of PCBM de-dimerization as a function of prior light intensity and duration. Our data reveal the presence of both “weakly” and “strongly” bound dimers, with higher light intensities preferentially generating the latter. DFT simulations corroborate our experimental findings and suggest a distribution of dimer binding energies, correlated with the orientation of the fullerene tail with respect to the dimer bonds on the cage. These results provide a framework to rationalize the double-edged effects of PCBM dimerization on the stability of organic solar cells.
-
Journal articleWay A, Luke J, Evans AD, et al., 2019,
Fluorine doped tin oxide as an alternative of indium tin oxide for bottom electrode of semi-transparent organic photovoltaic devices
, AIP Advances, Vol: 9, Pages: 085220-1-085220-5, ISSN: 2158-3226Indium tin oxide (ITO) is commonly used as the transparent bottom electrode for organic solar cells. However, it is known that the cost ofthe ITO is quite high due to the indium element, and in some studies ITO coated glass substrate is found to be the most expensive componentof device fabrication. Moreover, indium migration from ITO can cause stability issues in organic solar cells. Nevertheless, the use of ITO asthe bottom electrode is still dominating in the field. Here, we explore the possibility of using fluorine doped tin oxide (FTO) as an alternativeto ITO for the bottom electrode of organic solar cells particularly on semi-transparent cells. We present side-by-side comparisons on theiroptical, morphological and device properties and suggest that FTO could be more suitable than ITO as the bottom electrode for glass substratebased organic photovoltaic devices.
-
Journal articleSung MJ, Hong J, Cha H, et al., 2019,
Acene-Modified Small-Molecule Donors for Organic Photovoltaics
, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 25, Pages: 12316-12324, ISSN: 0947-6539- Author Web Link
- Cite
- Citations: 3
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.