Imperial College London

Dr Robert Hoye, FIMMM CEng CSci

Faculty of EngineeringDepartment of Materials

Honorary Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 6048r.hoye Website

 
 
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Location

 

2.27Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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87 results found

Zhang K, Gao Y, PInho B, Hoye R, Stranks S, Torrente-Murciano Let al., 2023, The importance of transport phenomena on the flow synthesis of monodispersed sharp blue-emitting perovskite CsPbBr3 nanoplatelets, Chemical Engineering Journal, Vol: 451, Pages: 1-9, ISSN: 1385-8947

This work demonstrates the importance of transport phenomena on the synthesis of halide perovskite nanoplatelets. Illustrated herein for CsPbBr3, we demonstrate the need for fast and homogeneous mixing to achieve monodispered crystals, in this case with sharp blue emission. The modularity of our synthesis method, combining fluid dynamic simulations, bespoke 3D flow reactors and on-line measurements (UV-vis absorbance and photoluminescence) reveals fundamental understanding about the growth of these perovskite nano-materials, which in turn leads to superlative size reducibility (2.2 ±0.3 nm) and properties (sharp blue emission at 472 nm wavelength, and PLQY 24.5±0.4%). The counterpart conventional hot injection batch synthesis with the same precursors, conditions and reaction temperature yields a product with PL at 501 nm with large batch to batch variations. Understanding the dynamics of the synthesis in the very early stages (within the first 100-300 ms) shows that mixing of the precursors plays a key role not only during the nucleation step, as previously believed, but also during the growth stage. Such fluid properties can be easily predicted in purposefully designed 3D microreactors to provide a consistent and steady output capable of fulfilling the large demand of blue light emitters for a variety of applications.

Journal article

Li Z, Huang Y-T, Mohan L, Zelewski S, Friend R, Briscoe J, Hoye Ret al., 2022, Elucidating the factors limiting the photovoltaic performance of mixed Sb-Bi halide elpasolite absorbers, Solar RRL, Vol: 6, Pages: 1-9, ISSN: 2367-198X

Although Cs2AgBiBr6 halide elpasolites have gained substantial attention as potential nontoxic and stable alternatives to lead-halide perovskites, they are limited by their wide bandgaps >2.2 eV. Alloying with Sb into the pnictogen site has been shown to be an effective method to lower the bandgap, but this has not translated into improvements in photovoltaic (PV) performance. In this work, the underlying causes are investigated. Pinhole-free films of Cs2Ag(SbxBi1-x)Br6 are achieved through antisolvent dripping, but PV devices still exhibit a reduction in power conversion efficiency (PCE) from 0.44±0.02% (without Sb) to 0.073±0.007% (90% Sb; lowest bandgap). There is a 0.7 V reduction in the open-circuit voltage, which correlates with the appearance of a sub-bandgap state approximately 0.7 eV below the optical bandgap in the Sb-containing elpasolite films, as found in both absorbance and photoluminescence measurements. Through detailed Williamson-Hall analysis, it is found that adding Sb into the elpasolite films leads to an increase in film strain. This strain is relieved through aerosol-assisted solvent treatment, which reduces both the sub-bandgap state density and energetic disorder in the films, as well as reducing the fast early decay in the photogenerated carrier population due to trap filling. This work shows that Sb alloying leads to the introduction of extra sub-bandgap states that limit the PV performance, but can be mitigated through post-annealing treatment to reduce disorder and strain.

Journal article

Huang Y-T, Kavanagh S, Righetto M, Rusu M, Levine I, Unold T, Zelewiski S, Sneyd A, Zhang K, Dai L, Britton A, Ye J, Julin J, Napari M, Zhang Z, Xiao J, Laitinen M, Torrente-Murciano L, Stranks S, Rao A, Herz L, Scanlon D, Walsh A, Hoye Ret al., 2022, Strong absorption and ultrafast localisation in NaBiS2 nanocrystals with slow charge-carrier recombination, Nature Communications, Vol: 13, ISSN: 2041-1723

I-V-VI2 ternary chalcogenides are gaining attention as earth-abundant, nontoxic, and air-stable absorbers for photovoltaic applications. However, the semiconductors explored thus far have slow absorption onsets, and their charge-carrier transport is not well understood yet. Herein, we investigate cation-disordered NaBiS2 nanocrystals, which have a steep absorption onset, with absorption coefficients reaching >105 cm-1 just above its pseudo-direct bandgap of 1.4 eV. Surprisingly, we also observe an ultrafast (at picosecond-time scale) photoconductivity decay and long-lived charge-carrier population persisting for over one microsecond in NaBiS2 nanocrystals. These unusual features arise because of the localised, non-bonding S p character of the upper valence band, which leads to a high density of electronic states at the band edges, ultrafast localisation of spatially-separated electrons and holes, as well as the slow decay of trapped holes. This work reveals the critical role of cation disorder in these systems on both absorption characteristics and charge-carrier kinetics.

Journal article

Andrei V, Ucoski GM, Pornrungroj C, Uswachoke C, Wang Q, Achilleos DS, Kasap H, Sokol KP, Jagt RA, Lu H, Lawson T, Wagner A, Pike SD, Wright DS, Hoye RLZ, MacManus-Driscoll JL, Joyce HJ, Friend RH, Reisner Eet al., 2022, Floating perovskite-BiVO4 devices for scalable solar fuel production, NATURE, Vol: 608, Pages: 518-+, ISSN: 0028-0836

Journal article

Ganose A, Scanlon D, Walsh A, Hoye Ret al., 2022, The defect challenge of wide-bandgap semiconductors for photovoltaics and beyond, Nature Communications, Vol: 13, ISSN: 2041-1723

The optoelectronic performance of wide-bandgap semiconductors often cannot compete with that of their defect-tolerant small-bandgap counterpart. Here, the authors outline three main challenges to overcome for mitigating the impact of defects in wide-bandgap semiconductors.

Journal article

Ye J, Li Z, Kubicki D, Zhang Y, Dai L, Otero Martinez C, Reus M, Arul R, DUDIPALA K, Andaji-Garmaroudi Z, Huang Y-T, Li Z, Chen Z, Muller-Buschbaum P, Yip H-L, Stranks S, Grey C, Baumberg J, Greenham N, Polavarapu L, Rao A, Hoye Ret al., 2022, Elucidating the role of antisolvents on the surface chemistry and optoelectronic properties of CsPbBrxI3-x perovskite nanocrystals, Journal of the American Chemical Society, Vol: 144, ISSN: 0002-7863

Colloidal lead-halide perovskite nanocrystals (LHP NCs) have emerged over the past decade as leading candidates for efficient next-generation optoelectronic devices, but their properties and performance critically depend on how they are purified. While antisolvents are widely used for purification, a detailed understanding of how the polarity of the antisolvent influences the surface chemistry and composition of the NCs is missing in the field. Here, we fill this knowledge gap by studying the surface chemistry of purified CsPbBrxI3-x NCs as the model system, which in itself is considered a promising candidate for pure-red light-emitting diodes and top-cells for tandem photovoltaics. Interestingly, we find that as the polarity of the antisolvent increases (from methyl acetate to acetone to butanol), there is a blueshift in the photoluminescence (PL) peak of the NCs along with a decrease in PL quantum yield (PLQY). Through transmission electron microscopy and X-ray photoemission spectroscopy measurements, we find that these changes in PL properties arise from antisolvent-induced iodide removal, which leads to a change in halide composition and, thus, the bandgap. Using detailed nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR) measurements along with density functional theory calculations, we propose that more polar antisolvents favor the detachment of the oleic acid and oleylamine ligands, which undergo amide condensation reactions, leading to the removal of iodide anions from the NC surface bound to these ligands. This work shows that careful selection of low-polarity antisolvents is a critical part of designing the synthesis of NCs to achieve high PLQYs with minimal defect-mediated phase segregation.

Journal article

Otero-Martinez C, Imran M, Schrenker N, Ye J, Ji K, Rao A, Stranks S, Hoye R, Bals S, Manna L, Pérez-Juste J, Polavarapu Let al., 2022, Fast A-site cation cross-exchange at room temperature: single-to double-and triple-cation halide perovskite nanocrystals, Angewandte Chemie International Edition, ISSN: 1433-7851

We report here fast A-site cation cross-exchange betweenAPbX3 perovskite nanocrystals (NCs) made of different A-cations (Cs(Cesium), FA (formamidinium), and MA (methylammonium)) at roomtemperature. Surprisingly, the A-cation cross-exchange proceeds asfast as the halide (X=Cl, Br, or I) exchange with the help of free Aoleate complexes present in the freshly prepared colloidal perovskiteNC solutions. It enabled the preparation of double (MACs, MAFA,CsFA)- and triple (MACsFA)-cation perovskite NCs with an opticalbandgap that is finely tunable by their A-site composition. The opticalspectroscopy together with structural analysis using XRD andatomically resolved high angle annular dark-field scanningtransmission electron microscopy (HAADF‐STEM) and integrateddifferential phase contrast (iDPC) STEM indicates the homogeneousdistribution of different cations in the mixed perovskite NC lattice.Unlike halide ions, the A-cations do not phase segregate under lightillumination.

Journal article

Byranvand M, Otero-Martinez C, Ye J, Zuo W, Manna L, Saliba M, Hoye R, Polavarapu Let al., 2022, Recent progress in mixed a-site cation halide perovskite thin-films and nanocrystals for solar cells and light-emitting diodes, Advanced Optical Materials, Vol: 10, ISSN: 2195-1071

Over the past few years, lead-halide perovskites (LHPs), both in the form of bulk thin films and colloidal nanocrystals (NCs), have revolutionized the field of optoelectronics, emerging at the forefront of next-generation optoelectronics. The power conversion efficiency (PCE) of halide perovskite solar cells has increased from 10% to over 25% over a short period of time and is very close to the theoretical limit (30%). At the same time, the external quantum efficiency (EQE) of perovskite LEDs has surpassed 23% and 20% for green and red emitters, respectively. Despite great progress in device efficiencies, the photoactive phase instability of perovskites is one of the major concerns for the long-term stability of the devices and is limiting their transition to commercialization. In this regard, researchers have found that the phase stability of LHPs and the reproducibility of the device performance can be improved by A-site cation alloying with two or more species, these are named mixed cation (double, triple, or quadruple) halide perovskites. This review provides a state-of-the-art overview of different types of mixed A-site cation bulk perovskite thin films and colloidal NCs reported in the literature, along with a discussion of their synthesis, properties, and progress in solar cells and LEDs.

Journal article

Pinho B, Zhang K, Hoye R, Torrente-Murciano Let al., 2022, Importance of monitoring the synthesis of light-interacting nanoparticles – a review on in-situ, ex-situ and online time-resolved studies, Advanced Optical Materials, Vol: 10, ISSN: 2195-1071

This review paper critically analyzes the importance of monitoring the synthesis of plasmonic and optoelectronic materials to not only provide a mechanistic understanding of their nucleation and growth but also crucial kinetic insights to enable their future development. Light-interacting nanoparticles present strong size-properties relationships, such that size control is at the core of any synthetic development. However, conventional ex-situ characterization of these materials has heavily limited their development to simple trial-and-error approaches. Over the last decade or so, the development of in-situ and online characterization capabilities has transformed our understanding, triggering a number of mechanistic models. In addition, time-resolved data have been able to reveal the steps rate, even for phenomena taking place in the microsecond scale (i.e. nucleation) thanks to the use of micro flow reactors. However, the literature contains a few disagreements and inaccuracies, which we consider to be due to the general lack of attention and control on mixing (especially relevant when mixing time is comparable to the reaction time) and the presence of additives during synthesis (e.g. stabilizers). Finally, we believe that recent in-situ monitoring development coupled with careful reactor design brings unique opportunities to not only synthesize nanoparticles in a reproducible and controllable manner but also to use data-rich approaches for self-regulated and automated systems.

Journal article

Yashwanth HJ, Rondiya S, Dzade N, Hoye R, Choudhary RJ, Phase DM, Dhole SD, Hareesh Ket al., 2022, Improved photocatalytic activity of TiO2 nanoparticles through nitrogen and phosphorus co-doped carbon quantum dots: an experimental and theoretical study, Physical Chemistry Chemical Physics, Vol: 24, Pages: 15271-15279, ISSN: 1463-9076

In this work, we develop a photocatalyst wherein nitrogen and phosphorus co-doped carbon quantum dots are scaffolded onto TiO2 nanoparticles (NPCQD/TiO2), denoted as NPCT hereafter. The developed NPCT photocatalyst exhibits an enhanced visible light photocatalytic hydrogen production of 533 μmol h−1 g−1 compared to nitrogen doped CQD/TiO2 (478 μmol h−1 g−1), phosphorus doped CQD/TiO2 (451 μmol h−1 g−1) and pure CQD/TiO2 (427 μmol h−1 g−1) photocatalysts. The enhanced photocatalytic activity of the NPCT photocatalyst is attributed to the excellent synergy between NPCQDs and TiO2 nanoparticles, which results in the creation of virtual energy levels, a decrease in work function and suppressed recombination rates, thereby increasing the lifetime of photogenerated electrons. A detailed mechanism is proposed for the enhancement in visible light hydrogen production by the NPCT photocatalyst from the experimental results, Mott–Schottky plots and ultraviolet photoelectron spectroscopy results. Further, first-principles density functional theory (DFT) simulations are carried out which predict the decrease in the work function and band gap, and the increase in the density of states of NPCT as the factors responsible for the observed enhancement in visible light photocatalytic hydrogen production.

Journal article

Andrei V, Jagt R, Rahaman M, Lari L, Lazarov V, MacManus-Driscoll J, Hoye R, Reisner Eet al., 2022, Long-term solar water and CO2 splitting with photoelectrochemical BiOI-BiVO4 tandems, Nature Materials, Vol: 21, Pages: 864-868, ISSN: 1476-1122

Photoelectrochemical (PEC) devices have been developed for direct solar fuel production, but the limited stability of submerged light absorbers hampers their commercial prospects.1,2 Here, we demonstrate photocathodes with an operational H2 evolution activity over weeks, by integrating a BiOI light absorber into a robust, oxide-based architecture with a graphite paste conductive encapsulant. In this case, the activity towards proton and CO2 reduction is mainly limited by catalyst degradation. We also introduce multiple-pixel devices as an innovative design principle for PEC systems, displaying superior photocurrents, onset biases and stability over corresponding conventional single-pixel devices. Accordingly, PEC tandem devices comprised of multiple-pixel BiOI photocathodes and BiVO4 photoanodes can sustain bias-free water splitting for 240 h, while devices with a Cu92In8 alloy catalyst demonstrate unassisted syngas production.

Journal article

Choi JW, Shin B, Gorai P, Hoye RLZ, Palgrave Ret al., 2022, Emerging earth-abundant solar absorbers, ACS Energy Letters, Vol: 7, Pages: 1553-1557, ISSN: 2380-8195

Developing solar absorbers that are efficient, low-cost, stable, and composed of nontoxic, Earth-abundant elements has long been the holy grail of next-generation photovoltaics (PV) research. (1) This effort has been disrupted by the advent and rapid rise in performance of solution-processable lead-halide perovskites. (2) One of the key enabling properties is the ability of these halide perovskites to tolerate point defects, enabling efficient PV performance despite high defect densities. (3,4) This discovery has reinvigorated efforts within the Earth-abundant PV community to design efficient solar absorbers, drawing inspiration from the halide perovskites, with particular focus on defect tolerance and achieving materials with long diffusion lengths. At the same time, the broad families of Earth-abundant solar absorbers provide valuable opportunities to overcome the toxicity and stability limitations of the lead-halide perovskites, without remaining confined solely within the perovskite family of compounds. The merging of these two communities has produced exciting new frontiers, which were explored in the recent symposium on “Earth-abundant next generation materials for solar energy” (Symposium F) at the 2021 Fall European Materials Research Society Meeting (held virtually). Herein, we feature some of the key emerging areas discussed at the Symposium: chalcogenide perovskites, II–IV–N2 compounds, antimony chalcogenides, and the computational search for novel defect-tolerant solar absorbers.

Journal article

Otero-Martinez C, Ye J, Sung J, Pastoriza-Santos I, Perez-Juste J, Xia Z, Rao A, Hoye RLZ, Polavarapu Let al., 2022, Colloidal Metal-Halide Perovskite Nanoplatelets: Thickness-Controlled Synthesis, Properties, and Application in Light-Emitting Diodes, ADVANCED MATERIALS, Vol: 34, ISSN: 0935-9648

Journal article

Hoye R, Hidalgo J, Jagt RA, Correa-Baena J-P, Fix T, MacManus-Driscoll JLet al., 2022, The role of dimensionality on the optoelectronic properties of oxide and halide perovskites, and their halide derivatives, Advanced Energy Materials, Vol: 12, ISSN: 1614-6832

Halide perovskite semiconductors have risen to prominence in photovoltaics and light-emitting diodes (LEDs), but traditional oxide perovskites, which overcome the stability limitations of their halide counterparts, have also recently witnessed a rise in potential as solar absorbers. One of the many important factors underpinning these developments is an understanding of the role of dimensionality on the optoelectronic properties and, consequently, on the performance of the materials in photovoltaics and LEDs. This review article examines the role of structural and electronic dimensionality, as well as form factor, in oxide and halide perovskites, and in lead-free alternatives to halide perovskites. Insights into how dimensionality influences the band gap, stability, charge-carrier transport, recombination processes and defect tolerance of the materials, and the impact these parameters have on device performance are brought forward. Particular emphasis is placed on carrier/exciton-phonon coupling, which plays a significant role in the materials considered, owing to their soft lattices and composition of heavy elements, and becomes more prominent as dimensionality is reduced. It is finished with a discussion of the implications on the classes of materials future efforts should focus on, as well as the key questions that need to be addressed.

Journal article

Senanayak S, Dai L, Kusch G, Shivanna R, Zhang Y, Pradhan D, Ye J, Huang Y-T, Sirringhaus H, Oliver R, Greenham N, Friend R, Hoye Ret al., 2021, Understanding the role of grain boundaries on charge-carrier and ion transport in Cs2AgBiBr6 thin films, Advanced Functional Materials, Vol: 31, Pages: 1-9, ISSN: 1616-301X

Halide double perovskites have gained significant attention, owing to their composition of low-toxicity elements, stability in air, and recent demonstrations of long charge-carrier lifetimes that can exceed 1 s. In particular, Cs2AgBiBr6 has been the subject of many investigations in photovoltaic devices. However, the efficiencies of solar cells based on this double perovskite are still far from the theoretical efficiency limit of the material. Here, we investigate the role of grain size on the optoelectronic properties of Cs2AgBiBr6 thin films. We show through cathodoluminescence measurements that grain boundaries are the dominant non-radiative recombination sites. We also demonstrate through field-effect transistor and temperature-dependent transient current measurements that grain boundaries act as the main channels for ion transport. Interestingly, we find a positive correlation between carrier mobility and temperature, which resembles the hopping mechanism often seen in organic semiconductors. These findings explain the discrepancy between the long diffusion lengths >1 m found in Cs2AgBiBr6 single crystals versus the limited performance achieved in their thin film counterparts. Our work shows that mitigating the impact of grain boundaries will be critical for these double perovskite thin films to reach the performance achievable based on their intrinsic single-crystal properties.

Journal article

Rondiya SR, Jagt RA, MacManus-Driscoll JL, Walsh A, Hoye RLZet al., 2021, Self-trapping in bismuth-based semiconductors: opportunities and challenges from optoelectronic devices to quantum technologies, Applied Physics Letters, Vol: 119, ISSN: 0003-6951

Semiconductors based on bismuth halides have gained attention for a wide range of electronic applications, including photovoltaics, light-emitting diodes, and radiation detectors. Their appeal is due to their low toxicity, high environmental stability under ambient conditions, and easy processability by a wide range of scalable methods. The performance of Bi-based semiconductors is dictated by electron–phonon interactions, which limit carrier mobilities and can also influence optoelectronic performance, for example, by giving rise to a large Stokes shift for photoluminescence, unavoidable energy loss channels, or shallow optical absorption onsets. In this Perspective, we discuss the recent understanding of how polarons and self-trapped excitons/carriers form in Bi-based semiconductors (particularly for the case of Cs2AgBiBr6), their impact on the optoelectronic properties of the materials, and the consequences on device performance. Finally, we discuss the opportunities that control of electron–phonon coupling enables, including stable solid-state white lighting, and the possibilities of exploiting the strong coupling found in bipolarons for quantum technologies.

Journal article

Rondiya SR, Jadhav YA, Zivkovic A, Jathar SB, Rahane GK, Cross RW, Rokade A, Devan RS, Kolekar S, Hoye RLZ, Ghosh HN, de Leeuw NH, Jadkar SR, Dzade NYet al., 2021, Solution-processed Cd-substituted CZTS nanocrystals for sensitized liquid junction solar cells, JOURNAL OF ALLOYS AND COMPOUNDS, Vol: 890, ISSN: 0925-8388

Journal article

Huang Y-T, Kavanagh SR, Scanlon DO, Walsh A, Hoye RLZet al., 2021, Perovskite-inspired materials for photovoltaics and beyond-from design to devices (vol 32, 132004, 2021), NANOTECHNOLOGY, Vol: 32, ISSN: 0957-4484

Journal article

Pecunia V, Occhipinti L, Hoye R, 2021, Emerging indoor photovoltaic technologies for sustainable internet of things, Advanced Energy Materials, Vol: 11, Pages: 131-131, ISSN: 1614-6832

The Internet of Things (IoT) provides everyday objects and environments with “intelligence” and data connectivity to improve quality of life and the efficiency of a wide range of human activities. However, the ongoing exponential growth of the IoT device ecosystem—up to tens of billions of units to date—poses a challenge regarding how to power such devices. This Progress Report discusses how energy harvesting can address this challenge. It then discusses how indoor photovoltaics (IPV) constitutes an attractive energy harvesting solution, given its deployability, reliability, and power density. For IPV to provide an eco-friendly route to powering IoT devices, it is crucial that its underlying materials and fabrication processes are low-toxicity and not harmful to the environment over the product life cycle. A range of IPV technologies—both incumbent and emerging—developed to date is discussed, with an emphasis on their environmental sustainability. Finally, IPV based on emerging lead-free perovskite-inspired absorbers are examined, highlighting their status and prospects for low-cost, durable, and efficient energy harvesting that is not harmful to the end user and environment. By examining emerging avenues for eco-friendly IPV, timely insight is provided into promising directions toward IPV that can sustainably power the IoT revolution.

Journal article

Silva JPB, Vieira EMF, Gwozdz K, Kaim A, Goncalves LM, MacManus-Driscoll JL, Hoye RLZ, Pereira Met al., 2021, High-performance self-powered photodetectors achieved through the pyro-phototronic effect in Si/SnOx/ZnO heterojunctions, NANO ENERGY, Vol: 89, ISSN: 2211-2855

Journal article

Dey A, Ye J, De A, Debroye E, Ha SK, Bladt E, Kshirsagar AS, Wang Z, Yin J, Wang Y, Quan LN, Yan F, Gao M, Li X, Shamsi J, Debnath T, Cao M, Scheel MA, Kumar S, Steele JA, Gerhard M, Chouhan L, Xu K, Wu X-G, Li Y, Zhang Y, Dutta A, Han C, Vincon I, Rogach AL, Nag A, Samanta A, Korgel BA, Shih C-J, Gamelin DR, Son DH, Zeng H, Zhong H, Sun H, Demir HV, Scheblykin IG, Mora-Sero I, Stolarczyk JK, Zhang JZ, Feldmann J, Hofkens J, Luther JM, Perez-Prieto J, Li L, Manna L, Bodnarchuk M, Kovalenko M, Roeffaers MBJ, Pradhan N, Mohammed OF, Bakr OM, Yang P, Muller-Buschbaum P, Kamat P, Bao Q, Zhang Q, Krahne R, Galian RE, Stranks SD, Bals S, Biju V, Tisdale WA, Yan Y, Hoye RLZ, Polavarapu Let al., 2021, State of the Art and Prospects for Halide Perovskite Nanocrystals, ACS NANO, Vol: 15, Pages: 10775-10981, ISSN: 1936-0851

Journal article

Pecunia V, Zhao J, Kim C, Tuttle BR, Mei J, Li F, Peng Y, Huq TN, Hoye RLZ, Kelly ND, Dutton SE, Xia K, MacManusDriscoll JL, Sirringhaus Het al., 2021, Assessing the impact of defects on lead‐free perovskite‐inspired photovoltaics via photoinduced current transient spectroscopy, Advanced Energy Materials, Vol: 11, ISSN: 1614-6832

The formidable rise of lead‐halide perovskite photovoltaics has energized the search for lead‐free perovskite‐inspired materials (PIMs) with related optoelectronic properties but free from toxicity limitations. The photovoltaic performance of PIMs closely depends on their defect tolerance. However, a comprehensive experimental characterization of their defect‐level parameters—concentration, energy depth, and capture cross‐section—has not been pursued to date, hindering the rational development of defect‐tolerant PIMs. While mainstream, capacitance‐based techniques for defect‐level characterization have sparked controversy in lead‐halide perovskite research, their use on PIMs is also problematic due to their typical near‐intrinsic character. This study demonstrates on four representative PIMs (Cs3Sb2I9, Rb3Sb2I9, BiOI, and AgBiI4) for which Photoinduced Current Transient Spectroscopy (PICTS) offers a facile, widely applicable route to the defect‐level characterization of PIMs embedded within solar cells. Going beyond the ambiguities of the current discussion of defect tolerance, a methodology is also presented to quantitatively assess the defect tolerance of PIMs in photovoltaics based on their experimental defect‐level parameters. Finally, PICTS applied to PIM photovoltaics is revealed to be ultimately sensitive to defect‐level concentrations <1 ppb. Therefore, this study provides a versatile platform for the defect‐level characterization of PIMs and related absorbers, which can catalyze the development of green, high‐performance photovoltaics.

Journal article

Nasane MP, Rondiya SR, Jadhav CD, Rahane GR, Cross RW, Jathar S, Jadhav Y, Barma S, Nilegave D, Jadkar V, Rokade A, Funde A, Chavan PG, Hoye RLZ, Dzade NY, Jadkar Set al., 2021, An interlinked computational-experimental investigation into SnS nanoflakes for field emission applications, New Journal of Chemistry: a journal for new directions in chemistry, Vol: 45, Pages: 11768-11779, ISSN: 1144-0546

Layered binary semiconductor materials have attracted significant interest as field emitters due to their low work function, mechanical stability, and high thermal, and electrical conductivity. Herein, we report a systematic experimental and theoretical investigation of SnS nanoflakes synthesized using a simple, low-cost, and non-toxic hot injection method for field emission studies. The field emission studies were carried out on SnS nanoflake thin films prepared using a simple spin coating technique. The X-ray diffraction (XRD) and Raman spectroscopy analysis revealed an orthorhombic phase of SnS. Scanning electron microscopy (SEM) analysis revealed that as-synthesized SnS has a flakes like morphology. The formation of pure-phase SnS nanoflakes was further confirmed by X-ray photoelectron spectroscopy (XPS) analysis. The UV-Visible-NIR spectroscopy analysis shows that SnS nanoflakes have a sharp absorption edge observed in the UV region and have a band gap of ∼1.66 eV. In addition, the first-principles density functional theory (DFT) calculations were carried out to provide atomic-level insights into the crystal structure, band structure, and density of states (DOS) of SnS nanoflakes. The field emission properties of SnS nanoflakes were also investigated and it was found that SnS nanoflakes have a low turn-on field (∼6.2 V μm−1 for 10 μA cm−2), high emission current density (∼104 μA cm−2 at 8.0 V μm−1), superior current stability (∼1 μA for ∼2.5 hrs), and a high field enhancement factor of 1735. First principles calculations predicted lower work function for different surfaces, especially for the most stable SnS (001) surface (ϕ = 4.32 eV), which is believed to be responsible for the observed facile electron emission characteristics. We anticipate that the SnS could be utilized for future vacuum nano/microelectronic and flat panel display applications due to the low turn-on field and flakes like structure.

Journal article

Perini C, Doherty T, Stranks S, Correa-Baena J-P, Hoye Ret al., 2021, Pressing challenges in halide perovskite photovoltaics - from the atomic to module level, Joule, Vol: 5, Pages: 1024-1030, ISSN: 2542-4351

Journal article

Napari M, Huq TN, Hoye RLZ, MacManusDriscoll JLet al., 2021, Nickel oxide thin films grown by chemical deposition techniques: Potential and challenges in next‐generation rigid and flexible device applications, InfoMat, Vol: 3, Pages: 536-576, ISSN: 2567-3165

Journal article

Polavarapu L, Ye J, Byranvand MM, Martínez CO, Hoye RL, Saliba Met al., 2021, Defect passivation in lead-halide perovskite nanocrystals and thin films: toward efficient LEDs and solar cells., Angewandte Chemie International Edition, ISSN: 1433-7851

Lead-halide perovskites (LHPs), in the form of both colloidal nanocrystals (NCs) and thin films, have emerged over the past decade as leading candidates for next-generation, efficient light-emitting diodes (LEDs) and solar cells. Owing to their high photoluminescence quantum yields (PLQYs), LHPs efficiently convert injected charge-carriers to light and vice versa . However, despite the defect-tolerance of LHPs, defects at the surface of colloidal NCs and at grain boundaries in thin films play a critical role in charge-carrier transport and non-radiative recombination, which lowers PLQYs, device efficiency and stability. Therefore, understanding the defects that play a key role in limiting performance, and developing effective passivation routes is critical for achieving advances in performance, and therefore features at the forefront of perovskite research. This review presents the current understanding of the defects in perovskites (both colloidal NCs and thin films) and their influence on the optical and charge-carrier transport properties. The review also discusses the passivation strategies toward improving the efficiencies of perovskite-based LEDs and solar cells.

Journal article

Gan J, Yu M, Hoye RLZ, Musselman KP, Li Y, Liu X, Zheng Y, Zu X, Li S, MacManus-Driscoll JL, Qiao Let al., 2021, Defects, photophysics and passivation in Pb-based colloidal quantum dot photovoltaics, Materials Today Nano, Vol: 13, Pages: 1-17, ISSN: 2588-8420

Colloidal quantum dots (CQDs) are a class of third-generation materials for photovoltaics (PVs) that are promising for enabling high efficiency devices with potential for exceeding the Shockley-Queisser limit. This is due to their potential to decrease thermal dissipation via multiple exciton generation during charge conversion and collection, which could potentially lead to an increase in the photovoltage or photocurrent in colloidal quantum dot photovoltaics (CQD PVs). But despite a predicted upper efficiency limit of 42%–44%, the highest power conversion efficiencies of these PVs using lead sulfide colloidal quantum dots (PbS CQDs) remains at approximately 13% on a laboratory scale. For further improvements, the fundamental recombination mechanisms need to be studied to determine their effects on the open-circuit voltage (VOC) and charge-carrier lifetime as well as the diffusion length of the carriers. Also, surface defect passivation and interface engineering should be studied. In this work, we discuss different pathways for non-radiative recombination losses in lead sulfide colloidal quantum dot photovoltaics (PbS CQD PVs), as well as the strategies for reducing these losses by the passivation of the surface and interface defects. We also discuss routes to overcome limits in the diffusion length of the carriers through the engineering of charge transport layers. This work provides routes for the fabrication of highly efficient CQD PVs.

Journal article

Napari M, Huq TN, Meeth DJ, Heikkilä MJ, Niang KM, Wang H, Iivonen T, Wang H, Leskelä M, Ritala M, Flewitt AJ, Hoye R, MacManus-Driscoll JLet al., 2021, Role of ALD Al2O3 surface passivation on the performance of p-type Cu2O thin film transistors, ACS Applied Materials and Interfaces, Vol: 13, Pages: 4156-4164, ISSN: 1944-8244

High-performance p-type oxide thin film transistors (TFTs) have great potential for many semiconductor applications. However, these devices typically suffer from low hole mobility and high off-state currents. We fabricated p-type TFTs with a phase-pure polycrystalline Cu2O semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD Al2O3 passivation layer on the Cu2O channel, followed by vacuum annealing at 300 °C. Detailed characterization by transmission electron microscopy–energy dispersive X-ray analysis and X-ray photoelectron spectroscopy shows that the surface of Cu2O is reduced following Al2O3 deposition and indicates the formation of a 1–2 nm thick CuAlO2 interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD Al2O3, leads to an improvement in the TFT performance by reducing the density of deep trap states as well as by reducing the accumulation of electrons in the semiconducting layer in the device off-state.

Journal article

Huang Y-T, Kavanagh S, Scanlon D, Walsh A, Hoye Ret al., 2021, Perovskite-inspired materials for photovoltaics and beyond – from design to devices, Nanotechnology, Vol: 32, Pages: 1-60, ISSN: 0957-4484

NanotechnologyACCEPTED MANUSCRIPT • The following article is Open accessPerovskite-Inspired Materials for Photovoltaics and Beyond – From Design to DevicesYi-Teng Huang1, Seán R. Kavanagh2, David O Scanlon3, Aron Walsh4 and Robert Hoye5Accepted Manuscript online 1 December 2020 • © 2020 The Author(s). Published by IOP Publishing Ltd.What is an Accepted Manuscript?Download Accepted Manuscript PDFDownload PDFArticle has an altmetric score of 6Turn on MathJaxShare this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on MendeleyArticle informationAbstractLead-halide perovskites have demonstrated astonishing increases in power conversion efficiency in photovoltaics over the last decade. The most efficient perovskite devices now outperform industry-standard multi-crystalline silicon solar cells, despite the fact that perovskites are typically grown at low temperature using simple solution-based methods. However, the toxicity of lead and its ready solubility in water are concerns for widespread implementation. These challenges, alongside the many successes of the perovskites, have motivated significant efforts across multiple disciplines to find lead-free and stable alternatives which could mimic the ability of the perovskites to achieve high performance with low temperature, facile fabrication methods. This Review discusses the computational and experimental approaches that have been taken to discover lead-free perovskite-inspired materials, and the recent successes and challenges in synthesizing these compounds. The atomistic origins of the extraordinary performance exhibited by lead-halide perovskites in photovoltaic devices is discussed, alongside the key challenges in engineering such high-performance in alternative, next-generation materials. Beyond photovoltaics, this Review discusses the impact perovskite-inspired materials have had in spurring efforts to apply new materials i

Journal article

Li Z, Kavanagh S, Napari M, Palgrave RG, Abdi-Jalebi M, Andaji-Garmaroudi Z, Davies DW, Laitinen M, Julin J, Isaacs MA, Friend RH, Scanlon DO, Walsh A, Hoye Ret al., 2020, Bandgap lowering in mixed alloys ofCs2Ag(SbxBi1-x)Br6 double perovskite thin films, Journal of Materials Chemistry A, Vol: 8, Pages: 21780-21788, ISSN: 2050-7488

Halide double perovskites have gained significant attention, owing to their composition of low-toxicity elements, stability in air and long charge-carrier lifetimes. However, most double perovskites, including Cs2AgBiBr6, have wide bandgaps, which limits photoconversion efficiencies. The bandgap can be reduced through alloying with Sb3+, but Sb-rich alloys are difficult to synthesize due to the high formation energy of Cs2AgSbBr6, which itself has a wide bandgap. We develop a solution-based route to synthesize phase-pure Cs2Ag(SbxBi1−x)Br6 thin films, with the mixing parameter x continuously varying over the entire composition range. We reveal that the mixed alloys (x between 0.5 and 0.9) demonstrate smaller bandgaps than the pure Sb- and Bi-based compounds. The reduction in the bandgap of Cs2AgBiBr6 achieved through alloying (170 meV) is larger than if the mixed alloys had obeyed Vegard's law (70 meV). Through in-depth computations, we propose that bandgap lowering arises from the type II band alignment between Cs2AgBiBr6 and Cs2AgSbBr6. The energy mismatch between the Bi and Sb s and p atomic orbitals, coupled with their non-linear mixing, results in the alloys adopting a smaller bandgap than the pure compounds. Our work demonstrates an approach to achieve bandgap reduction and highlights that bandgap bowing may be found in other double perovskite alloys by pairing together materials forming a type II band alignment.

Journal article

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