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Abstract: The low-temperature performance of mixed-composition perovskite solar cells (PSCs) reflects the complex interplay among thermal effects, bandgap renormalization, and structural phase behavior. Temperature-dependent structural, optical, and electrical measurements reveal a maximum power conversion efficiency at 263 K, which coincides with the onset of the cubic-tetragonal phase coexistence. At this temperature, symmetry lowering is observed, accompanied by a split emission band and increased current–voltage hysteresis, consistent with structural heterogeneity. Device simulations show that any benefit from mixed-phase band alignment is conditional on effective interphase passivation. Consequently, the mixed phase is best described as a loss-minimum condition at well-passivated cubic–tetragonal interphases with stable collection. Our findings identify a narrow mixed-phase window in which phase coexistence couples to the optoelectronic response and enhances the device performance, providing fundamental insight into temperature-dependent structure–property relations in hybrid perovskites.
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Dec 2025
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I09-Surface and Interface Structural Analysis
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Stefania
Riva
,
Fredrik O. L.
Johansson
,
Sergei M.
Butorin
,
Corrado
Comparotto
,
Olivier
Donzel-Gargand
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Henry
Nameirakpam
,
M. Venkata
Kamalakar
,
Soham
Mukherjee
,
Jonathan J. S.
Scragg
,
Hakan
Rensmo
Open Access
Abstract: The chalcogenide perovskite BaZrS3 is a semiconductor that exhibits a high absorption coefficient and is composed of earth-abundant elements, making it a promising candidate for sustainable optoelectronic devices. To integrate BaZrS3 thin films into devices, one needs to obtain clean surfaces and characterize them thoroughly. Herein, we report a sputtering-annealing method to produce clean surfaces of prefabricated BaZrS3 thin films with varying metal ratios (Ba-rich, stoichiometric, and Zr-rich). This method combines Ar sputtering with high-temperature annealing (600 and 750 °C) in ultra-high vacuum. Depth-profiling via photoelectron spectroscopy with soft (950 eV) and hard X-rays (6.6 keV) confirms that this processing route substantially mitigates undesired surface oxidation of the films, revealing predominantly core level peaks characteristic of the BaZrS3 perovskite. As a drawback, the sputtering process also produces Zr0, which persists in the Zr-rich sample even after the annealing treatment. In contrast, the Ba-rich and stoichiometric BaZrS3 samples converge to similar surface compositions free of Zr0, and the low roughness of the Ba-rich thin film indicates its preference for device integration. While the thermal treatment modifies the surface chemistry, the bulk characteristics, e.g., nominal metal-ratio, orthorhombic structure, and crystallite sizes, remain unaffected. However, high-temperature annealing affects band realignment with respect to the Fermi level, resulting in n-type doping characteristics. By correlating the experimentally measured valence band to the density functional theory calculated molecular orbital picture, we assign the valence band features to specific elemental orbitals and their interactions. The proposed cleaning procedure has the potential to advance the application of BaZrS3 in layered devices, such as photovoltaic cells and photodetectors.
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Aug 2025
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I09-Surface and Interface Structural Analysis
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Bhavya
Rakheja
,
Adam
Hultqvist
,
Rahul Mahavir
Varma
,
Natalia M.
Martin
,
Karen
Radetzky
,
Stefania
Riva
,
Evelyn
Johannesson
,
Ute B.
Cappel
,
Hakan
Rensmo
,
Erik M. J.
Johansson
,
Tobias
Torndahl
Diamond Proposal Number(s):
[35209]
Open Access
Abstract: Tin oxide (SnOx) by atomic-layer deposition (ALD), in combination with fullerene, is widely employed as an electron transport layer in p–i–n perovskite solar cells. This study investigates the direct deposition of ALD SnOx on top of formamidinium (FA)-based perovskites, as a step toward the elimination of the fullerene interlayer and its poor effect on solar cell’s long-term stability. The interfacial chemistry between FA-based perovskites (FAPbI3 and FAPbBr3) and ALD SnOx was studied using soft and hard X-ray photoelectron spectroscopy (SOXPES and HAXPES) with a focus on investigating the separate roles FA and different halides play during interface formation. FAPbI3 and FAPbBr3 solar cell structures solely containing ALD SnOx resulted in s-shaped current–voltage characteristics, indicating the formation of a transport barrier at the interface. Both SOXPES and HAXPES measurements revealed the emergence of additional nitrogen states at the interface during the ALD SnOx deposition on FAPbI3 and FAPbBr3, where these states are linked to the decomposition of FA+. The FAPbI3/ALD SnOx interface also showed the presence of lead iodide (PbI2) through additional lead states other than that from FAPbI3 by using SOXPES measurements. Concerning the FAPbBr3/ALD SnOx interface, no additional lead states were observed; however, measurements instead revealed the formation of Sn–Br bonds at the interface along with the migration of bromine ions into the bulk of the ALD SnOx. Thus, FAPbI3 and FAPbBr3 undergo distinct reaction pathways upon direct deposition of ALD SnOx on top of them. We reason that the decomposition of FA+ in both perovskites and the formation of PbI2 at the FAPbI3/ALD SnOx interface and the incorporation of Br in SnOx at the FAPbBr3/ALD SnOx interface prove detrimental toward device performance. Therefore, careful interfacial engineering that can mitigate the formation of these products should be utilized to enhance the performance of perovskite solar cells.
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Jun 2025
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[36397]
Abstract: Niobium–based Wadsley–Roth oxides have recently attracted attention as promising anode materials for lithium-ion batteries, providing high charging and discharging rates and cycling stability. The higher operating potential of Wadsley–Roth oxide anodes, while impacting the overall energy density, reduces the risk of dendrite formation, making them safer at high power densities. We present the rapid preparation of two Wadsley–Roth oxide compounds, AlNb11O29 and Ti2Nb10O29, by a microwave-assisted preparation method in under 10 min starting from oxide materials, and heating in open crucibles. No further processing is required to make effective electrode materials from these compounds other than grinding with the usual conducting carbon and binder. High-resolution synchrotron X-ray diffraction and scanning electron microscopy are employed to understand the impact of rapid preparation on the structure and morphology. Excellent electrochemical performance is achieved, with reversible capacities of up to 250 mAh g–1 with high capacity retention over 100 cycles and fast-charging rates up to 10C without much loss of capacity. The materials reported here are compared to reports from the literature. Despite the very similar structures and compositions, AlNb11O29 is found to be less effective as an anode material than Ti2Nb10O29, and in this work, we delve into possible reasons for this.
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May 2025
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[25166]
Open Access
Abstract: The peritectic compound Li4(OH)3Br has been suggested as a candidate material for latent heat thermal energy storage (TES), due to its high calculated melting enthalpy (804 J g–1) around 300 °C, however experimental reports have obtained much lower values (≤250 J g–1). In this work, we show that the crystal structure established for Li4(OH)3Br in literature corresponds to a metastable hydrated compound, and instead propose that the thermodynamically stable phase belongs to the Pmnm space group. The hydrated phase dehydrates at ∼175 °C, rendering the exceptional previous predictions inapplicable. An experimentally measured melting enthalpy of 263 ± 3 J g–1 is found for high-purity Li4(OH)3Br. Theoretical modeling is used to suggest a crystal structure for Li4(OH)3Br, from which a melting enthalpy of 260 J g–1 is calculated, in good agreement with the experimental work, and supporting that nonetheless impressive storage capacity at ∼290 °C can be offered by Li4(OH)3Br.
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Apr 2025
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I14-Hard X-ray Nanoprobe
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Dominic
Blackburn
,
Nathan S.
Hill
,
Christopher J.
Wood
,
Tamilselvan
Velusamy
,
Balder A.
Nieto-Díaz
,
Caitlin
Woolley
,
Andy
Brown
,
Loukas
Zampelis
,
Trevor
Mcardle
,
Molly
Worth
,
Timothy
Thornber
,
Ibrahim
Albariqi
,
Rachel C.
Kilbride
,
Tingxiang
Yang
,
C. Neil
Hunter
,
Graham J.
Leggett
,
George
Koutsourakis
,
James C.
Blakesley
,
Fernando A.
Castro
,
David
Beynon
,
Trystan M.
Watson
,
Dumitru
Sirbu
,
David G.
Lidzey
Diamond Proposal Number(s):
[32789]
Open Access
Abstract: We fabricate a type of back-contact perovskite solar cell based on 1.5 μm-width grooves that are embossed into a plastic film whose opposing “walls” are selectively coated with either n- or p-type contacts. A perovskite precursor solution is then deposited into the grooves, creating individual photovoltaic devices. Each groove device is series-connected to its neighbors, creating minimodules consisting of hundreds of connected grooves. Here, we report on the fabrication of groove-based devices using slot-die coating to deposit the perovskite precursor and explore the structure of the perovskite in the grooves using a range of microscopy and spectroscopy techniques. Significantly, our devices do not contain any expensive or scarce elements such as indium, indicating that this technology is both sustainable and low-cost. Furthermore, all coating processes explored here were performed using roll-to-roll processing techniques. Our technology is therefore completely scalable and is consistent with high-throughput, low-cost manufacturing.
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Feb 2025
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[32266]
Abstract: Organic solar cells (OSCs) are attracting significant attention due to their low cost, lightweight, and flexible nature. The introduction of nonfullerene acceptors (NFAs) has propelled OSC development into a transformative era. However, the limited availability of wide band gap polymer donors for NFAs poses a critical challenge, hindering further advancements. This study examines the role of developed wide band gap halogenated pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (PPD)-based polymers, in combination with the Y6 nonfullerene acceptor, in bulk heterojunction (BHJ) OSCs. We first focus on the electronic and absorbance modifications brought about by halogen substitution in PPD-based polymers, revealing how these adjustments influence the HOMO/LUMO energy levels and, subsequently, photovoltaic performance. Despite the increased Voc of halogenated polymers due to the optimal band alignment, power conversion efficiencies (PCEs) were decreased due to suboptimal blend morphologies. We second implemented PPD as a solid additive to PM6:Y6, forming ternary OSCs and further improving the PCE. The study provides a nuanced understanding of the interplay between molecular design, device morphology, and OSC performance and opens insights for future research to achieve an optimal balance between band alignment and favorable blend morphology for high-efficiency OSCs.
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Jan 2025
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B18-Core EXAFS
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Diamond Proposal Number(s):
[29271]
Open Access
Abstract: Photocatalytic CO2 reduction, including reaction rate, product selectivity, and longevity, is highly sensitive to the coordination structure of the catalytic active sites, and the precise design of the active site remains a challenge in heterogeneous catalysts. Herein, we report on the modulation of the coordination structure of MNx-type active sites (M = Co or Ni; x = 4 or 5) anchored on a periodic mesoporous organosilica (PMO) support to improve photocatalytic CO2 reduction. The PMO was functionalized with pendant 3,6-di(2′-pyridyl)pyridazine (dppz) groups to allow immobilization of molecular Co and Ni complexes with polypyridine ligands. A comparative analysis of CO2 photoreduction in the presence of an organic photosensitizer (4CzIPN, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene) and a conventional [Ru(bpy)3]Cl2 sensitizer revealed strong influence of the coordination environment on the catalytic performance. CoN5-PMO demonstrated a superior CO2 photoreduction activity than the other materials and displayed a cobalt-based turnover number (TONCO) of 92 for CO evolution at ∼75% selectivity after 3 h irradiation in the presence of 4CzIPN. The hybrid CoN5-PMO catalyst exhibited better activity than its homogeneous [CoN5] counterpart, indicating that the heterogenization promotes the formation of isolated active sites with improved longevity and faster catalytic rate.
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Jun 2024
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I19-Small Molecule Single Crystal Diffraction
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Eman A. A.
Alkhudhayr
,
Dumitru
Sirbu
,
Miriam
Fsadni
,
Benjamin
Vella
,
Bening T.
Muhammad
,
Paul G.
Waddell
,
Michael R.
Probert
,
Thomas J.
Penfold
,
Toby
Hallam
,
Elizabeth
Gibson
,
Pablo
Docampo
Diamond Proposal Number(s):
[302080]
Open Access
Abstract: Organic–inorganic hybrid halide perovskite solar cells (PSCs) have attracted substantial attention from the photovoltaic research community, with the power conversion efficiency (PCE) already exceeding 26%. Current state-of-the-art devices rely on Spiro-OMeTAD as the hole-transporting material (HTM); however, Spiro-OMeTAD is costly due to its complicated synthesis and expensive product purification, while its low conductivity ultimately limits the achievable device efficiency. In this work, we build upon our recently introduced family of low-cost amide-based small molecules and introduce a molecule (termed TPABT) that results in high conductivity values (∼10–5 S cm–1 upon addition of standard ionic additives), outperforming our previous amide-based material (EDOT-Amide-TPA, ∼10–6 S cm–1) while only costing an estimated $5/g. We ascribe the increased optoelectronic properties to favorable molecular packing, as shown by single-crystal X-ray diffraction, which results in close spacing between the triphenylamine blocks. This, in turn, results in a short hole-hopping distance between molecules and therefore good mobility and conductivity. In addition, TPABT exhibits a higher bandgap and is as a result more transparent in the visible range of the solar spectrum, leading to lower parasitic absorption losses than Spiro-OMeTAD, and has increased moisture stability. We applied the molecule in perovskite solar cells and obtained good efficiency values in the ∼15% range. Our approach shows that engineering better molecular packing may be the key to developing high-efficiency, low-cost HTMs for perovskite solar cells.
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Nov 2023
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[21742]
Open Access
Abstract: Zn1–xSnxOy (ZTO) deposited by atomic layer deposition has shown promising results as a buffer layer material for kesterite Cu2ZnSnS4 (CZTS) thin film solar cells. Increased performance was observed when a ZTO buffer layer was used as compared to the traditional CdS buffer, and the performance was further increased after an air annealing treatment of the absorber. In this work, we study how CZTS absorber surface treatments may influence the chemical and electronic properties at the ZTO/CZTS interface and the reactions that may occur at the absorber surface prior to atomic layer deposition of the buffer layer. For this, we have used a combination of microscopy and synchrotron-based spectroscopies with variable information depths (X-ray photoelectron spectroscopy, high-energy X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy), allowing for an in-depth analysis of the CZTS near-surface regions and bulk material properties. No significant ZTO buffer thickness variation is observed for the differently treated CZTS absorbers, and no differences are observed when comparing the bulk properties of the samples. However, the formation of SnOx and compositional changes observed toward the CZTS surface upon an air annealing treatment may be linked to the modified buffer layer growth. Further, the results indicate that the initial N2 annealing step integrated in the buffer layer growth by atomic layer deposition, which removes Na–COx species from the CZTS surface, may be useful for the ZTO/CZTS device performance.
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Oct 2022
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