I19-Small Molecule Single Crystal Diffraction
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Cara J.
Hawkins
,
Jon A.
Newnham
,
Batoul
Almoussawi
,
Nataliya L.
Gulay
,
Samuel L.
Goodwin
,
Marco
Zanella
,
Troy D.
Manning
,
Luke M.
Daniels
,
Matthew S.
Dyer
,
Tim D.
Veal
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Diamond Proposal Number(s):
[30461]
Open Access
Abstract: Mixed anion halide-chalcogenide materials have recently attracted attention for a variety of applications, owing to their desirable optoelectronic properties. We report the synthesis of a previously unreported mixed-metal chalcohalide material, CuBiSeCl2 (Pnma), accessed through a simple, low-temperature solid-state route. The physical structure is characterized through single-crystal X-ray diffraction and reveals significant Cu displacement within the CuSe2Cl4 octahedra. The electronic structure of CuBiSeCl2 is investigated computationally, which indicates highly anisotropic charge carrier effective masses, and by experimental verification using X-ray photoelectron spectroscopy, which reveals a valence band dominated by Cu orbitals. The band gap is measured to be 1.33(2) eV, a suitable value for solar absorption applications. The electronic and thermal properties, including resistivity, Seebeck coefficient, thermal conductivity, and heat capacity, are also measured, and it is found that CuBiSeCl2 exhibits a low room temperature thermal conductivity of 0.27(4) W K–1 m–1, realized through modifications to the phonon landscape through increased bonding anisotropy.
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Apr 2024
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I09-Surface and Interface Structural Analysis
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Theodore D. C.
Hobson
,
Luke
Thomas
,
Laurie J,
Phillips
,
Leanne A. H.
Jones
,
Matthew J.
Smiles
,
Christopher H.
Don
,
Pardeep K.
Thakur
,
Huw
Shiel
,
Stephen
Campbell
,
Vincent
Barrioz
,
Vin
Dhanak
,
Tim
Veal
,
Jonathan D.
Major
,
Ken
Durose
Diamond Proposal Number(s):
[31170]
Open Access
Abstract: We explored the in-situ doping of cadmium telluride thin films with indium to produce n-type absorbers as an alternative to the near-universal choice of p-type for photovoltaic devices. The films were grown by close space sublimation from melt-synthesised feedstock. Transfer of the indium during film growth was limited to 0.0014 – 0.014% - unless reducing conditions were used which yielded 14 – 28% efficient transport. While chunks of bulk feedstock were verified as n-type by the hot probe method, carrier type of thin film material was only able to be verified by using hard x-ray photoelectron spectroscopy to determine the Fermi level position within the band gap. The assignment of n-type conductivity was consistent with the rectification behaviour of a p-InP/CdTe:In junction. However, chloride treatment had the effect of compensating n-CdTe:In to near-intrinsic levels. Without chloride, the highest dopant activation was 20% of the chemical concentration of indium, this being for a film having a carrier concentration of n = 2 x 1015 cm-3. However, the activation was often much lower, and compensation due to over-doping with indium and native defects (stoichiometry) are discussed. Results from preliminary bifacial devices comprising Au/P3HT/ZnTe/CdTe:In/CdS/FTO/glass are presented.
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Sep 2023
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I09-Surface and Interface Structural Analysis
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Christopher H.
Don
,
Thomas P.
Shalvey
,
Matthew J.
Smiles
,
Luke
Thomas
,
Laurie J.
Phillips
,
Theodore D. C.
Hobson
,
Harry
Finch
,
Leanne A. H.
Jones
,
Jack E. N.
Swallow
,
Nicole
Fleck
,
Christopher
Markwell
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Deepnarayan
Biswas
,
Leon
Bowen
,
Benjamin A. D.
Williamson
,
David O.
Scanlon
,
Vinod R.
Dhanak
,
Ken
Durose
,
Tim D.
Veal
,
Jonathan D.
Major
Diamond Proposal Number(s):
[32696]
Open Access
Abstract: Despite the recent success of CdS/Sb2Se3 heterojunction devices, cadmium toxicity, parasitic absorption from the relatively narrow CdS band gap (2.4 eV) and multiple reports of inter-diffusion at the interface forming Cd(S,Se) and Sb2(S,Se)3 phases, present significant limitations to this device architecture. Among the options for alternative partner layers in antimony chalcogenide solar cells, the wide band gap, non-toxic titanium dioxide (TiO2) has demonstrated the most promise. It is generally accepted that the anatase phase of the polymorphic TiO2 is preferred, although there is currently an absence of analysis with regard to phase influence on device performance. This work reports approaches to distinguish between TiO2 phases using both surface and bulk characterization methods. A device fabricated with a radio frequency (RF) magnetron sputtered rutile-TiO2 window layer (FTO/TiO2/Sb2Se3/P3HT/Au) achieved an efficiency of 6.88% and near-record short–circuit current density (Jsc) of 32.44 mA cm−2, which is comparable to established solution based TiO2 fabrication methods that produced a highly anatase-TiO2 partner layer and a 6.91% efficiency device. The sputtered method introduces reproducibility challenges via the enhancement of interfacial charge barriers in multi-phase TiO2 films with a rutile surface and anatase bulk. This is shown to introduce severe S-shaped current–voltage (J–V) distortion and a drastic fill–factor (FF reduction in these devices.
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Jun 2023
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I09-Surface and Interface Structural Analysis
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Leanne A. H.
Jones
,
Zongda
Xing
,
Jack E. N.
Swallow
,
Huw
Shiel
,
Thomas J.
Featherstone
,
Matthew J.
Smiles
,
Nicole
Fleck
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Laurence J.
Hardwick
,
David O.
Scanlon
,
Anna
Regoutz
,
Tim D.
Veal
,
Vinod R.
Dhanak
Diamond Proposal Number(s):
[25980]
Open Access
Abstract: A comprehensive study of bulk molybdenum dichalcogenides is presented with the use of soft and hard X-ray photoelectron (SXPS and HAXPES) spectroscopy combined with hybrid density functional theory (DFT). The main core levels of MoS2, MoSe2, and MoTe2 are explored. Laboratory-based X-ray photoelectron spectroscopy (XPS) is used to determine the ionization potential (IP) values of the MoX2 series as 5.86, 5.40, and 5.00 eV for MoSe2, MoSe2, and MoTe2, respectively, enabling the band alignment of the series to be established. Finally, the valence band measurements are compared with the calculated density of states which shows the role of p-d hybridization in these materials. Down the group, an increase in the p-d hybridization from the sulfide to the telluride is observed, explained by the configuration energy of the chalcogen p orbitals becoming closer to that of the valence Mo 4d orbitals. This pushes the valence band maximum closer to the vacuum level, explaining the decreasing IP down the series. High-resolution SXPS and HAXPES core-level spectra address the shortcomings of the XPS analysis in the literature. Furthermore, the experimentally determined band alignment can be used to inform future device work.
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Dec 2022
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I09-Surface and Interface Structural Analysis
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Adam J.
Jackson
,
Benjamin J.
Parrett
,
Joe
Willis
,
Alex M.
Ganose
,
W. W. Winnie
Leung
,
Yuhan
Liu
,
Benjamin A. D.
Williamson
,
Timur K.
Kim
,
Moritz
Hoesch
,
Larissa S. I.
Veiga
,
Raman
Kalra
,
Jens
Neu
,
Charles A.
Schmuttenmaer
,
Tien-Lin
Lee
,
Anna
Regoutz
,
Tung-Chun
Lee
,
Tim D.
Veal
,
Robert G.
Palgrave
,
Robin
Perry
,
David O.
Scanlon
Diamond Proposal Number(s):
[24449]
Open Access
Abstract: Transparent conducting oxides have become ubiquitous in modern optoelectronics. However, the number of oxides that are transparent to visible light and have the metallic-like conductivity necessary for applications is limited to a handful of systems that have been known for the past 40 years. In this work, we use hybrid density functional theory and defect chemistry analysis to demonstrate that tri-rutile zinc antimonate, ZnSb2O6, is an ideal transparent conducting oxide and to identify gallium as the optimal dopant to yield high conductivity and transparency. To validate our computational predictions, we have synthesized both powder samples and single crystals of Ga-doped ZnSb2O6 which conclusively show behavior consistent with a degenerate transparent conducting oxide. This study demonstrates the possibility of a family of Sb(V)-containing oxides for transparent conducting oxide and power electronics applications.
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Oct 2022
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I09-Surface and Interface Structural Analysis
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Theodore D. C.
Hobson
,
Huw
Shiel
,
Christopher N.
Savory
,
Jack E. N.
Swallow
,
Leanne A. H.
Jones
,
Thomas J.
Featherstone
,
Matthew J.
Smiles
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Bhaskar
Das
,
Chris
Leighton
,
Guillaume
Zoppi
,
Vin R.
Dhanak
,
David O.
Scanlon
,
Tim D.
Veal
,
Ken
Durose
,
Jonathan D.
Major
Diamond Proposal Number(s):
[23160]
Open Access
Abstract: Antimony selenide (Sb2Se3) is a promising absorber material for thin-film
photovoltaics. However, certain areas of fundamental understanding of this material
remain incomplete and this presents a barrier to further efficiency gains. In particular,
recent studies have highlighted the role of majority carrier type and extrinsic doping
in drastically changing the performance of high efficiency devices [1]. Herein, Sndoped
Sb2Se3 bulk crystals are shown to exhibit p-type conductivity using Hall effect
and hot-probe measurements. The measured conductivities are higher than those
achieved through native defects alone, but with a carrier density (up to 7.4 × 1014
cm−3) several orders of magnitude smaller than the quantity of Sn included in the
source material. Additionally, a combination of ultraviolet, X-ray and hard X-ray
photoemission spectroscopies are employed to obtain a non-destructive depth profile of
the valence band maximum, confirming p-type conductivity and indicating a majority
carrier type inversion layer at the surface. Finally, these results are supported by
density functional theory calculations of the defect formation energies in Sn-doped
Sb2Se3, showing a possible limit on the carrier concentration achievable with Sn as
a dopant. This study sheds light on the effectiveness of Sn as a p-type dopant in
Sb2Se3 and highlights avenues for further optimisation of doped Sb2Se3 for solar energy
devices.
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Sep 2022
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I09-Surface and Interface Structural Analysis
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Laura E.
Ratcliff
,
Takayoshi
Oshima
,
Felix
Nippert
,
Benjamin M.
Janzen
,
Elias
Kluth
,
Rüdiger
Goldhahn
,
Martin
Feneberg
,
Piero
Mazzolini
,
Oliver
Bierwagen
,
Charlotte
Wouters
,
Musbah
Nofal
,
Martin
Albrecht
,
Jack E. N.
Swallow
,
Leanne A. H.
Jones
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Curran
Kalha
,
Christoph
Schlueter
,
Tim D.
Veal
,
Joel B.
Varley
,
Markus R.
Wagner
,
Anna
Regoutz
Diamond Proposal Number(s):
[21430, 24670]
Open Access
Abstract: Ga2O3 and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga2O3 offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ-Ga2O3 presents a particular challenge across synthesis, characterisation, and theory due to its inherent disorder and resulting complex structure – electronic structure relationship. Here, density functional theory is used in combination with a machine learning approach to screen nearly one million potential structures, thereby developing a robust atomistic model of the γ-phase. Theoretical results are compared with surface and bulk sensitive soft and hard X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, spectroscopic ellipsometry, and photoluminescence excitation spectroscopy experiments representative of the occupied and unoccupied states of γ-Ga2O3. The first onset of strong absorption at room temperature is found at 5.1 eV from spectroscopic ellipsometry, which agrees well with the excitation maximum at 5.17 eV obtained by PLE spectroscopy, where the latter shifts to 5.33 eV at 5 K. This work presents a leap forward in the treatment of complex, disordered oxides and is a crucial step towards exploring how their electronic structure can be understood in terms of local coordination and overall structure.
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Jul 2022
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I09-Surface and Interface Structural Analysis
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Luke
Thomas
,
Theo D. C.
Hobson
,
Laurie J.
Phillips
,
Kieran J.
Cheetham
,
Neil
Tarbuck
,
Leanne A. H.
Jones
,
Matthew J.
Smiles
,
Chris H.
Don
,
Pardeep K.
Thakur
,
Mark
Isaacs
,
Huw
Shiel
,
Stephen
Campbell
,
Vincent
Barrioz
,
Vin
Dhanak
,
Tim
Veal
,
Jonathan D.
Major
,
Ken
Durose
Diamond Proposal Number(s):
[28268]
Open Access
Abstract: This paper is motivated by the potential advantages of higher doping and lower contact barriers in CdTe photovoltaic devices that may be realized by using n- type rather than the conventional p-type solar absorber layers. We present post-growth doping trials for indium in thin polycrystalline CdTe films using diffusion of indium metal and with indium chloride. Chemical concentrations of indium up to 1019 cm-3 were achieved and the films were verified as n-type by hard x-ray photoemission. Post growth chlorine treatment (or InCl3) was found to compensate the n-doping. Trial structures comprising CdS/CdTe:In verified that the doped absorber structures performed as expected both before and after chloride treatment, but it is recognized that this is not an optimum combination. Hence in order to identify how the advantages of n-type absorbers might be fully realized in future work, we also report simulations of a range of p-n junction combinations with n-CdTe, a number of which have the potential for high Voc.
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Jun 2022
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I09-Surface and Interface Structural Analysis
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Matthew J.
Smiles
,
Thomas
Shalvey
,
Luke
Thomas
,
Theodore D. C.
Hobson
,
Leanne A. H.
Jones
,
Laurie
Phillips
,
Christopher
Don
,
Thomas
Beesley
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Ken
Durose
,
Jonathan D.
Major
,
Tim
Veal
Diamond Proposal Number(s):
[31170]
Open Access
Abstract: Germanium selenide (GeSe) bulk crystals, thin films and solar cells are investigated with a focus on acceptor-doping with silver (Ag) and the use of an Sb2Se3 interfacial layer. The Ag-doping of GeSe occurred by a stoichiometric melt growth technique that created Ag-doped GeSe bulk crystals. A combination of capacitance voltage measurements, synchrotron radiation photoemission spectroscopy and surface space-charge calculations indicate Ag-doping increases the hole density from 5.2×1015 cm-3 to 1.9×1016 cm-3. The melt-grown material is used as the source for thermally evaporated GeSe films within solar cells. The cell structure with the highest efficiency of 0.260% is FTO/CdS/Sb2Se3/undoped-GeSe/Au compared with solar cells without the Sb2Se3 interfacial layer or with the Ag-doped GeSe.
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Apr 2022
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I09-Surface and Interface Structural Analysis
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Matthew J.
Smiles
,
Jonathan M.
Skelton
,
Huw
Shiel
,
Leanne A. H.
Jones
,
Jack E. N.
Swallow
,
Holly J.
Edwards
,
Thomas
Featherstone
,
Philip A. E.
Murgatroyd
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Vinod R.
Dhanak
,
Tim D.
Veal
Diamond Proposal Number(s):
[21431, 23160]
Open Access
Abstract: Germanium sulfide and germanium selenide bulk crystals were prepared using a melt growth technique. X-ray photoemission spectroscopy (XPS) was used to determine ionisation potentials of 5.74 and 5.48 eV for GeS and GeSe respectively. These values were used with the previously-measured band gaps to establish the natural band alignments with potential window layers for solar cells and to identify CdS and TiO2 as sensible choices. The ionisation potential of GeS is found to be smaller than in comparable materials. Using XPS and hard x-ray photoemission (HAXPES) measurements in conjunction with density-functional theory calculations, we demonstrate that stereochemically active Ge 4s lone pairs are present at the valence-band maxima. Our work thus provides direct evidence for active lone pairs in GeS and GeSe, with important implications for the applications of these and related materials, such as Ge-based perovskites.
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Sep 2021
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