51
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Shamsi J, Rainò G, Kovalenko MV, Stranks SD. To nano or not to nano for bright halide perovskite emitters. NATURE NANOTECHNOLOGY 2021; 16:1164-1168. [PMID: 34759354 DOI: 10.1038/s41565-021-01005-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
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52
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Li Z, Bretscher H, Zhang Y, Delport G, Xiao J, Lee A, Stranks SD, Rao A. Mechanistic insight into the chemical treatments of monolayer transition metal disulfides for photoluminescence enhancement. Nat Commun 2021; 12:6044. [PMID: 34663820 PMCID: PMC8523741 DOI: 10.1038/s41467-021-26340-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 09/17/2021] [Indexed: 11/29/2022] Open
Abstract
There is a growing interest in obtaining high quality monolayer transition metal disulfides for optoelectronic applications. Surface treatments using a range of chemicals have proven effective to improve the photoluminescence yield of these materials. However, the underlying mechanism for the photoluminescence enhancement is not clear, which prevents a rational design of passivation strategies. Here, a simple and effective approach to significantly enhance the photoluminescence is demonstrated by using a family of cation donors, which we show to be much more effective than commonly used p-dopants. We develop a detailed mechanistic picture for the action of these cation donors and demonstrate that one of them, bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI), enhances the photoluminescence of both MoS2 and WS2 to a level double that of the currently best performing super-acid trifluoromethanesulfonimide (H-TFSI) treatment. In addition, the ionic salts used in our treatments are compatible with greener solvents and are easier to handle than super-acids, providing the possibility of performing treatments during device fabrication. This work sets up rational selection rules for ionic chemicals to passivate transition metal disulfides and increases their potential in practical optoelectronic applications.
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53
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Liu D, Luo D, Iqbal AN, Orr KWP, Doherty TAS, Lu ZH, Stranks SD, Zhang W. Strain analysis and engineering in halide perovskite photovoltaics. NATURE MATERIALS 2021; 20:1337-1346. [PMID: 34531574 DOI: 10.1038/s41563-021-01097-x] [Citation(s) in RCA: 85] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Accepted: 08/05/2021] [Indexed: 06/13/2023]
Abstract
Halide perovskites are a compelling candidate for the next generation of clean-energy-harvesting technologies owing to their low cost, facile fabrication and outstanding semiconductor properties. However, photovoltaic device efficiencies are still below practical limits and long-term stability challenges hinder their practical application. Current evidence suggests that strain in halide perovskites is a key factor in dictating device efficiency and stability. Here we outline the fundamentals of strain within halide perovskites relevant to photovoltaic applications and rationalize approaches to characterize the phenomenon. We examine recent breakthroughs in eliminating the adverse impacts of strain, enhancing both device efficiencies and operational stabilities. Finally, we discuss further challenges and outline future research directions for placing stress and strain studies at the forefront of halide perovskite research. An extensive understanding of strain in halide perovskites is needed, which would allow effective strain management and drive further enhancements in efficiencies and stabilities of perovskite photovoltaics.
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54
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Dey K, Roose B, Stranks SD. Optoelectronic Properties of Low-Bandgap Halide Perovskites for Solar Cell Applications. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2102300. [PMID: 34432925 DOI: 10.1002/adma.202102300] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Revised: 06/11/2021] [Indexed: 05/24/2023]
Abstract
Riding on the coat tails of rapid developments in single-junction halide perovskite solar cells, all-perovskite multijunction solar cells have recently garnered significant attention, with the highest power-conversion efficiency already reaching 25.6%. Much of this progress has been fueled by the rapid rise in the photovoltaic performance of low-bandgap halide perovskite absorbers, materials, which, to date, have only been achievable by the partial or complete substitution of lead with tin. However, much room still exists to develop a more critical understanding of key material properties in these low-bandgap perovskites. Herein, the key optoelectronic properties of absorption, carrier generation, recombination, and transport in these tin-containing perovskites are discussed, showing that intrinsic doping distinctively impacts many of these properties, thereby rendering this class of halide perovskites unique within the family. Current understanding of the mechanisms that degrade optoelectronic performance in these materials and the corresponding devices are also summarized. These collective results highlight an important interplay between doping, defects, and degradation that will need to be controlled. Finally, the current gaps in understanding of these low-bandgap perovskites are outlined, thereby providing guidelines for further research, which will unlock their full potential for realizing a plethora of high-performance optoelectronic devices.
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55
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Moseley ODI, Doherty TAS, Parmee R, Anaya M, Stranks SD. Halide perovskites scintillators: unique promise and current limitations. JOURNAL OF MATERIALS CHEMISTRY. C 2021; 9:11588-11604. [PMID: 34671480 PMCID: PMC8444306 DOI: 10.1039/d1tc01595h] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Accepted: 05/28/2021] [Indexed: 05/31/2023]
Abstract
The widespread use of X- and gamma-rays in a range of sectors including healthcare, security and industrial screening is underpinned by the efficient detection of the ionising radiation. Such detector applications are dominated by indirect detectors in which a scintillating material is combined with a photodetector. Halide perovskites have recently emerged as an interesting class of semiconductors, showing enormous promise in optoelectronic applications including solar cells, light-emitting diodes and photodetectors. Here, we discuss how the same superior semiconducting properties that have catalysed their rapid development in these optoelectronic devices, including high photon attenuation and fast and efficient emission properties, also make them promising scintillator materials. By outlining the key mechanisms of their operation as scintillators, we show why reports of remarkable performance have already emerged, and describe how further learning from other optoelectronic devices will propel forward their applications as scintillators. Finally, we outline where these materials can make the greatest impact in detector applications by maximally exploiting their unique properties, leading to dramatic improvements in existing detection systems or introducing entirely new functionality.
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56
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Nagane S, Macpherson S, Hope MA, Kubicki DJ, Li W, Verma SD, Ferrer Orri J, Chiang YH, MacManus-Driscoll JL, Grey CP, Stranks SD. Tetrafluoroborate-Induced Reduction in Defect Density in Hybrid Perovskites through Halide Management. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2102462. [PMID: 34219285 DOI: 10.1002/adma.202102462] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 05/13/2021] [Indexed: 05/06/2023]
Abstract
Hybrid-perovskite-based optoelectronic devices are demonstrating unprecedented growth in performance, and defect passivation approaches are highly promising routes to further improve properties. Here, the effect of the molecular ion BF4 - , introduced via methylammonium tetrafluoroborate (MABF4 ) in a surface treatment for MAPbI3 perovskite, is reported. Optical spectroscopy characterization shows that the introduction of tetrafluoroborate leads to reduced non-radiative charge-carrier recombination with a reduction in first-order recombination rate from 6.5 × 106 to 2.5 × 105 s-1 in BF4 - -treated samples, and a consequent increase in photoluminescence quantum yield by an order of magnitude (from 0.5 to 10.4%). 19 F, 11 B, and 14 N solid-state NMR is used to elucidate the atomic-level mechanism of the BF4 - additive-induced improvements, revealing that the BF4 - acts as a scavenger of excess MAI by forming MAI-MABF4 cocrystals. This shifts the equilibrium of iodide concentration in the perovskite phase, thereby reducing the concentration of interstitial iodide defects that act as deep traps and non-radiative recombination centers. These collective results allow us to elucidate the microscopic mechanism of action of BF4 - .
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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 XG, Li Y, Zhang Y, Dutta A, Han C, Vincon I, Rogach AL, Nag A, Samanta A, Korgel BA, Shih CJ, Gamelin DR, Son DH, Zeng H, Zhong H, Sun H, Demir HV, Scheblykin IG, Mora-Seró I, Stolarczyk JK, Zhang JZ, Feldmann J, Hofkens J, Luther JM, Pérez-Prieto J, Li L, Manna L, Bodnarchuk MI, Kovalenko MV, Roeffaers MBJ, Pradhan N, Mohammed OF, Bakr OM, Yang P, Müller-Buschbaum P, Kamat PV, Bao Q, Zhang Q, Krahne R, Galian RE, Stranks SD, Bals S, Biju V, Tisdale WA, Yan Y, Hoye RLZ, Polavarapu L. State of the Art and Prospects for Halide Perovskite Nanocrystals. ACS NANO 2021; 15:10775-10981. [PMID: 34137264 PMCID: PMC8482768 DOI: 10.1021/acsnano.0c08903] [Citation(s) in RCA: 332] [Impact Index Per Article: 110.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Accepted: 05/04/2021] [Indexed: 05/10/2023]
Abstract
Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.
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Grants
- from U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division
- Ministry of Education, Culture, Sports, Science and Technology
- European Research Council under the European Unionâ??s Horizon 2020 research and innovation programme (HYPERION)
- Ministry of Education - Singapore
- FLAG-ERA JTC2019 project PeroGas.
- Deutsche Forschungsgemeinschaft
- Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy
- EPSRC
- iBOF funding
- Agencia Estatal de Investigaci�ón, Ministerio de Ciencia, Innovaci�ón y Universidades
- National Research Foundation Singapore
- National Natural Science Foundation of China
- Croucher Foundation
- US NSF
- Fonds Wetenschappelijk Onderzoek
- National Science Foundation
- Royal Society and Tata Group
- Department of Science and Technology, Ministry of Science and Technology
- Swiss National Science Foundation
- Natural Science Foundation of Shandong Province, China
- Research 12210 Foundation?Flanders
- Japan International Cooperation Agency
- Ministry of Science and Innovation of Spain under Project STABLE
- Generalitat Valenciana via Prometeo Grant Q-Devices
- VetenskapsrÃÂ¥det
- Natural Science Foundation of Jiangsu Province
- KU Leuven
- Knut och Alice Wallenbergs Stiftelse
- Generalitat Valenciana
- Agency for Science, Technology and Research
- Ministerio de EconomÃÂa y Competitividad
- Royal Academy of Engineering
- Hercules Foundation
- China Association for Science and Technology
- U.S. Department of Energy
- Alexander von Humboldt-Stiftung
- Wenner-Gren Foundation
- Welch Foundation
- Vlaamse regering
- European Commission
- Bayerisches Staatsministerium für Wissenschaft, Forschung und Kunst
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58
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Bretscher H, Li Z, Xiao J, Qiu DY, Refaely-Abramson S, Alexander-Webber JA, Tanoh A, Fan Y, Delport G, Williams CA, Stranks SD, Hofmann S, Neaton JB, Louie SG, Rao A. Correction to "Rational Passivation of Sulfur Vacancy Defects in Two-Dimensional Transition Metal Dichalcogenides". ACS NANO 2021; 15:10734. [PMID: 34124883 PMCID: PMC8504790 DOI: 10.1021/acsnano.1c04628] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Indexed: 06/12/2023]
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59
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Tennyson E, Frohna K, Drake WK, Sahli F, Chien-Jen Yang T, Fu F, Werner J, Chosy C, Bowman AR, Doherty TAS, Jeangros Q, Ballif C, Stranks SD. Multimodal Microscale Imaging of Textured Perovskite-Silicon Tandem Solar Cells. ACS ENERGY LETTERS 2021; 6:2293-2304. [PMID: 34307879 PMCID: PMC8291767 DOI: 10.1021/acsenergylett.1c00568] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 05/14/2021] [Indexed: 05/02/2023]
Abstract
Halide perovskite/crystalline silicon (c-Si) tandem solar cells promise power conversion efficiencies beyond the limits of single-junction cells. However, the local light-matter interactions of the perovskite material embedded in this pyramidal multijunction configuration, and the effect on device performance, are not well understood. Here, we characterize the microscale optoelectronic properties of the perovskite semiconductor deposited on different c-Si texturing schemes. We find a strong spatial and spectral dependence of the photoluminescence (PL) on the geometrical surface constructs, which dominates the underlying grain-to-grain PL variation found in halide perovskite films. The PL response is dependent upon the texturing design, with larger pyramids inducing distinct PL spectra for valleys and pyramids, an effect which is mitigated with small pyramids. Further, optimized quasi-Fermi level splittings and PL quantum efficiencies occur when the c-Si large pyramids have had a secondary smoothing etch. Our results suggest that a holistic optimization of the texturing is required to maximize light in- and out-coupling of both absorber layers and there is a fine balance between the optimal geometrical configuration and optoelectronic performance that will guide future device designs.
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60
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Bretscher H, Li Z, Xiao J, Qiu DY, Refaely-Abramson S, Alexander-Webber JA, Tanoh A, Fan Y, Delport G, Williams CA, Stranks SD, Hofmann S, Neaton JB, Louie SG, Rao A. Rational Passivation of Sulfur Vacancy Defects in Two-Dimensional Transition Metal Dichalcogenides. ACS NANO 2021; 15:8780-8789. [PMID: 33983711 PMCID: PMC8158852 DOI: 10.1021/acsnano.1c01220] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Accepted: 05/07/2021] [Indexed: 06/01/2023]
Abstract
Structural defects vary the optoelectronic properties of monolayer transition metal dichalcogenides, leading to concerted efforts to control defect type and density via materials growth or postgrowth passivation. Here, we explore a simple chemical treatment that allows on-off switching of low-lying, defect-localized exciton states, leading to tunable emission properties. Using steady-state and ultrafast optical spectroscopy, supported by ab initio calculations, we show that passivation of sulfur vacancy defects, which act as exciton traps in monolayer MoS2 and WS2, allows for controllable and improved mobilities and an increase in photoluminescence up to 275-fold, more than twice the value achieved by other chemical treatments. Our findings suggest a route for simple and rational defect engineering strategies for tunable and switchable electronic and excitonic properties through passivation.
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61
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Ferrer Orri J, Tennyson EM, Kusch G, Divitini G, Macpherson S, Oliver RA, Ducati C, Stranks SD. Using pulsed mode scanning electron microscopy for cathodoluminescence studies on hybrid perovskite films. NANO EXPRESS 2021. [DOI: 10.1088/2632-959x/abfe3c] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Abstract
The use of pulsed mode scanning electron microscopy cathodoluminescence (CL) for both hyperspectral mapping and time-resolved measurements is found to be useful for the study of hybrid perovskite films, a class of ionic semiconductors that have been shown to be beam sensitive. A range of acquisition parameters is analysed, including beam current and beam mode (either continuous or pulsed operation), and their effect on the CL emission is discussed. Under optimized acquisition conditions, using a pulsed electron beam, the heterogeneity of the emission properties of hybrid perovskite films can be resolved via the acquisition of CL hyperspectral maps. These optimized parameters also enable the acquisition of time-resolved CL of polycrystalline films, showing significantly shorter lived charge carriers dynamics compared to the photoluminescence analogue, hinting at additional electron beam-specimen interactions to be further investigated. This work represents a promising step to investigate hybrid perovskite semiconductors at the nanoscale with CL.
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62
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Baldwin A, Delport G, Leng K, Chahbazian R, Galkowski K, Loh KP, Stranks SD. Local Energy Landscape Drives Long-Range Exciton Diffusion in Two-Dimensional Halide Perovskite Semiconductors. J Phys Chem Lett 2021; 12:4003-4011. [PMID: 33877840 PMCID: PMC8154849 DOI: 10.1021/acs.jpclett.1c00823] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Accepted: 04/12/2021] [Indexed: 05/15/2023]
Abstract
Halide perovskites are versatile semiconductors with applications including photovoltaics and light-emitting devices, having modular optoelectronic properties realizable through composition and dimensionality tuning. Layered Ruddlesden-Popper perovskites are particularly interesting due to their unique 2D character and charge carrier dynamics. However, long-range energy transport through exciton diffusion in these materials is not understood or realized. Here, local time-resolved luminescence mapping techniques are employed to visualize exciton transport in exfoliated flakes of the BA2MAn-1PbnI3n+1 perovskite family. Two distinct transport regimes are uncovered, depending on the temperature range. Above 100 K, diffusion is mediated by thermally activated hopping processes between localized states. At lower temperatures, a nonuniform energy landscape emerges in which transport is dominated by downhill energy transfer to lower-energy states, leading to long-range transport over hundreds of nanometers. Efficient, long-range, and switchable downhill transfer offers exciting possibilities for controlled directional long-range transport in these 2D materials for new applications.
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63
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Xiao J, Liu Y, Steinmetz V, Caglar M, Mc Hugh J, Baikie T, Gauriot N, Nguyen M, Ruggeri E, Andaji-Garmaroudi Z, Stranks SD, Legrand L, Barisien T, Friend RH, Greenham NC, Rao A, Pandya R. Correction to Optical and Electronic Properties of Colloidal CdSe Quantum Rings. ACS NANO 2021; 15:3540. [PMID: 33512988 DOI: 10.1021/acsnano.1c00060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
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64
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Bowman AR, Lang F, Chiang YH, Jiménez-Solano A, Frohna K, Eperon GE, Ruggeri E, Abdi-Jalebi M, Anaya M, Lotsch BV, Stranks SD. Relaxed Current Matching Requirements in Highly Luminescent Perovskite Tandem Solar Cells and Their Fundamental Efficiency Limits. ACS ENERGY LETTERS 2021; 6:612-620. [PMID: 33614966 PMCID: PMC7887871 DOI: 10.1021/acsenergylett.0c02481] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2020] [Accepted: 01/12/2021] [Indexed: 05/27/2023]
Abstract
Perovskite-based tandem solar cells are of increasing interest as they approach commercialization. Here we use experimental parameters from optical spectroscopy measurements to calculate the limiting efficiency of perovskite-silicon and all-perovskite two-terminal tandems, employing currently available bandgap materials, as 42.0% and 40.8%, respectively. We show luminescence coupling between subcells (the optical transfer of photons from the high-bandgap to low-bandgap subcell) relaxes current matching when the high-bandgap subcell is a luminescent perovskite. We calculate that luminescence coupling becomes important at charge trapping rates (≤106 s-1) already being achieved in relevant halide perovskites. Luminescence coupling increases flexibility in subcell thicknesses and tolerance to different spectral conditions. For maximal benefit, the high-bandgap subcell should have the higher short-circuit current under average spectral conditions. This can be achieved by reducing the bandgap of the high-bandgap subcell, allowing wider, unstable bandgap compositions to be avoided. Lastly, we visualize luminescence coupling in an all-perovskite tandem through cross-section luminescence imaging.
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65
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Yang X, Luo D, Xiang Y, Zhao L, Anaya M, Shen Y, Wu J, Yang W, Chiang YH, Tu Y, Su R, Hu Q, Yu H, Shao G, Huang W, Russell TP, Gong Q, Stranks SD, Zhang W, Zhu R. Buried Interfaces in Halide Perovskite Photovoltaics. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2006435. [PMID: 33393159 DOI: 10.1002/adma.202006435] [Citation(s) in RCA: 80] [Impact Index Per Article: 26.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Revised: 11/15/2020] [Indexed: 05/14/2023]
Abstract
Understanding the fundamental properties of buried interfaces in perovskite photovoltaics is of paramount importance to the enhancement of device efficiency and stability. Nevertheless, accessing buried interfaces poses a sizeable challenge because of their non-exposed feature. Herein, the mystery of the buried interface in full device stacks is deciphered by combining advanced in situ spectroscopy techniques with a facile lift-off strategy. By establishing the microstructure-property relations, the basic losses at the contact interfaces are systematically presented, and it is found that the buried interface losses induced by both the sub-microscale extended imperfections and lead-halide inhomogeneities are major roadblocks toward improvement of device performance. The losses can be considerably mitigated by the use of a passivation-molecule-assisted microstructural reconstruction, which unlocks the full potential for improving device performance. The findings open a new avenue to understanding performance losses and thus the design of new passivation strategies to remove imperfections at the top surfaces and buried interfaces of perovskite photovoltaics, resulting in substantial enhancement in device performance.
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66
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Abfalterer A, Shamsi J, Kubicki DJ, Savory CN, Xiao J, Divitini G, Li W, Macpherson S, Gałkowski K, MacManus-Driscoll JL, Scanlon DO, Stranks SD. Colloidal Synthesis and Optical Properties of Perovskite-Inspired Cesium Zirconium Halide Nanocrystals. ACS MATERIALS LETTERS 2020; 2:1644-1652. [PMID: 33313512 PMCID: PMC7724740 DOI: 10.1021/acsmaterialslett.0c00393] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Accepted: 10/27/2020] [Indexed: 06/01/2023]
Abstract
Optoelectronic devices based on lead halide perovskites are processed in facile ways, yet are remarkably efficient. There are extensive research efforts investigating lead-free perovskite and perovskite-related compounds, yet there are challenges to synthesize these materials in forms that can be directly integrated into thin film devices rather than as bulk powders. Here, we report on the colloidal synthesis and characterization of lead-free, antifluorite Cs2ZrX6 (X = Cl, Br) nanocrystals that are readily processed into thin films. We use transmission electron microscopy and powder X-ray diffraction measurements to determine their size and structural properties, and solid-state nuclear magnetic resonance measurements reveal the presence of oleate ligand, together with a disordered distribution of Cs surface sites. Density functional theory calculations reveal the band structure and fundamental band gaps of 5.06 and 3.91 eV for Cs2ZrCl6 and Cs2ZrBr6, respectively, consistent with experimental values. Finally, we demonstrate that the Cs2ZrCl6 and Cs2ZrBr6 nanocrystal thin films exhibit tunable, broad white photoluminescence with quantum yields of 45% for the latter, with respective peaks in the blue and green spectral regions and mixed systems exhibiting properties between them. Our work represents a critical step toward the application of lead-free Cs2ZrX6 nanocrystal thin films into next-generation light-emitting applications.
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67
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Tanoh AOA, Gauriot N, Delport G, Xiao J, Pandya R, Sung J, Allardice J, Li Z, Williams CA, Baldwin A, Stranks SD, Rao A. Directed Energy Transfer from Monolayer WS 2 to Near-Infrared Emitting PbS-CdS Quantum Dots. ACS NANO 2020; 14:15374-15384. [PMID: 33078943 PMCID: PMC8155326 DOI: 10.1021/acsnano.0c05818] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Accepted: 10/15/2020] [Indexed: 05/24/2023]
Abstract
Heterostructures of two-dimensional (2D) transition metal dichalcogenides (TMDs) and inorganic semiconducting zero-dimensional (0D) quantum dots (QDs) offer useful charge and energy transfer pathways, which could form the basis of future optoelectronic devices. To date, most have focused on charge transfer and energy transfer from QDs to TMDs, that is, from 0D to 2D. Here, we present a study of the energy transfer process from a 2D to 0D material, specifically exploring energy transfer from monolayer tungsten disulfide (WS2) to near-infrared emitting lead sulfide-cadmium sulfide (PbS-CdS) QDs. The high absorption cross section of WS2 in the visible region combined with the potentially high photoluminescence (PL) efficiency of PbS QD systems makes this an interesting donor-acceptor system that can effectively use the WS2 as an antenna and the QD as a tunable emitter, in this case, downshifting the emission energy over hundreds of millielectron volts. We study the energy transfer process using photoluminescence excitation and PL microscopy and show that 58% of the QD PL arises due to energy transfer from the WS2. Time-resolved photoluminescence microscopy studies show that the energy transfer process is faster than the intrinsic PL quenching by trap states in the WS2, thus allowing for efficient energy transfer. Our results establish that QDs could be used as tunable and high PL efficiency emitters to modify the emission properties of TMDs. Such TMD-QD heterostructures could have applications in light-emitting technologies or artificial light-harvesting systems or be used to read out the state of TMD devices optically in various logic and computing applications.
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68
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Xiao J, Liu Y, Steinmetz V, Çaǧlar M, Mc Hugh J, Baikie T, Gauriot N, Nguyen M, Ruggeri E, Andaji-Garmaroudi Z, Stranks SD, Legrand L, Barisien T, Friend RH, Greenham NC, Rao A, Pandya R. Optical and Electronic Properties of Colloidal CdSe Quantum Rings. ACS NANO 2020; 14:14740-14760. [PMID: 33044058 DOI: 10.1021/acsnano.0c01752] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Luminescent colloidal CdSe nanorings are a recently developed type of semiconductor structure that have attracted interest due to the potential for rich physics arising from their nontrivial toroidal shape. However, the exciton properties and dynamics of these materials with complex topology are not yet well understood. Here, we use a combination of femtosecond vibrational spectroscopy, temperature-resolved photoluminescence (PL), and single-particle measurements to study these materials. We find that on transformation of CdSe nanoplatelets to nanorings, by perforating the center of platelets, the emission lifetime decreases and the emission spectrum broadens due to ensemble variations in the ring size and thickness. The reduced PL quantum yield of nanorings (∼10%) compared to platelets (∼30%) is attributed to an enhanced coupling between (i) excitons and CdSe LO-phonons at 200 cm-1 and (ii) negatively charged selenium-rich traps, which give nanorings a high surface charge (∼-50 mV). Population of these weakly emissive trap sites dominates the emission properties with an increased trap emission at low temperatures relative to excitonic emission. Our results provide a detailed picture of the nature of excitons in nanorings and the influence of phonons and surface charge in explaining the broad shape of the PL spectrum and the origin of PL quantum yield losses. Furthermore, they suggest that the excitonic properties of nanorings are not solely a consequence of the toroidal shape but also a result of traps introduced by puncturing the platelet center.
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Kubicki D, Saski M, MacPherson S, Gal̷kowski K, Lewiński J, Prochowicz D, Titman JJ, Stranks SD. Halide Mixing and Phase Segregation in Cs 2AgBiX 6 (X = Cl, Br, and I) Double Perovskites from Cesium-133 Solid-State NMR and Optical Spectroscopy. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2020; 32:8129-8138. [PMID: 33071455 PMCID: PMC7558408 DOI: 10.1021/acs.chemmater.0c01255] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Revised: 09/16/2020] [Indexed: 05/02/2023]
Abstract
All-inorganic double perovskites (elpasolites) are a promising potential alternatives to lead halide perovskites in optoelectronic applications. Although halide mixing is a well-established strategy for band gap tuning, little is known about halide mixing and phase segregation phenomena in double perovskites. Here, we synthesize a wide range of single- and mixed-halide Cs2AgBiX6 (X = Cl, Br, and I) double perovskites using mechanosynthesis and probe their atomic-level microstructure using 133Cs solid-state MAS NMR. We show that mixed Cl/Br materials form pure phases for any Cl/Br ratio while Cl/I and Br/I mixing is only possible within a narrow range of halide ratios (<3 mol % I) and leads to a complex mixture of products for higher ratios. We characterize the optical properties of the resulting materials and show that halide mixing does not lead to an appreciable tunability of the PL emission. We find that iodide incorporation is particularly pernicious in that it quenches the PL emission intensity and radiative charge carrier lifetimes for iodide ratios as low as 0.3 mol %. Our study shows that solid-state NMR, in conjunction with optical spectroscopies, provides a comprehensive understanding of the structure-activity relationships, halide mixing, and phase segregation phenomena in Cs2AgBiX6 (X = Cl, Br, and I) double perovskites.
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70
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Roose B, Dey K, Chiang YH, Friend RH, Stranks SD. Critical Assessment of the Use of Excess Lead Iodide in Lead Halide Perovskite Solar Cells. J Phys Chem Lett 2020; 11:6505-6512. [PMID: 32693601 DOI: 10.1021/acs.jpclett.0c01820] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
It is common practice in the lead halide perovskite solar cell field to add a small molar excess of lead iodide (PbI2) to the precursor solution to increase the device performance. However, recent reports have shown that an excess of PbI2 can accelerate performance loss. In addition, PbI2 is photoactive (band gap ∼2.3 eV), which may lead to parasitic absorption losses in a solar cell. Here we show that devices using small quantities of excess PbI2 exhibit better device performance as compared with stoichiometric devices, both initially and for the duration of a stability test under operating conditions, primarily by enhancing the charge extraction. However, the photolysis of PbI2 negates the beneficial effect on charge extraction by leaving voids in the perovskite film and introduces trap states that are detrimental for device performance. We propose that although excess PbI2 provides a good template for enhanced performance, the community must continue to seek other additives or synthesis routes that fulfill the same beneficial role as excess PbI2, but without the photolysis that negates these beneficial effects under long-term device operation.
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71
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Chiang YH, Anaya M, Stranks SD. Multisource Vacuum Deposition of Methylammonium-Free Perovskite Solar Cells. ACS ENERGY LETTERS 2020; 5:2498-2504. [PMID: 32832697 PMCID: PMC7437071 DOI: 10.1021/acsenergylett.0c00839] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Accepted: 06/25/2020] [Indexed: 05/05/2023]
Abstract
Halide perovskites of the form ABX3 have shown outstanding properties for solar cells. The highest reported compositions consist of mixtures of A-site cations methylammonium (MA), formamidinium (FA) and cesium, and X-site iodide and bromide ions, and are produced by solution processing. However, it is unclear whether solution processing will yield sufficient spatial performance uniformity for large-scale photovoltaic modules or compatibility with deposition of multilayered tandem solar cell stacks. In addition, the volatile MA cation presents long-term stability issues. Here, we report the multisource vacuum deposition of FA0.7Cs0.3Pb(I0.9Br0.1)3 perovskite thin films with high-quality morphological, structural, and optoelectronic properties. We find that the controlled addition of excess PbI2 during the deposition is critical for achieving high performance and stability of the absorber material, and we fabricate p-i-n solar cells with stabilized power output of 18.2%. We also reveal the sensitivity of the deposition process to a range of parameters, including substrate, annealing temperature, evaporation rates, and source purity, providing a guide for further evaporation efforts. Our results demonstrate the enormous promise for MA-free perovskite solar cells employing industry-scalable multisource evaporation processes.
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Bowman AR, Anaya M, Greenham NC, Stranks SD. Quantifying Photon Recycling in Solar Cells and Light-Emitting Diodes: Absorption and Emission Are Always Key. PHYSICAL REVIEW LETTERS 2020; 125:067401. [PMID: 32845686 DOI: 10.1103/physrevlett.125.067401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Revised: 04/09/2020] [Accepted: 06/24/2020] [Indexed: 05/12/2023]
Abstract
Photon recycling has received increased attention in recent years following its observation in halide perovskites. It has been shown to lower the effective bimolecular recombination rate and thus increase excitation densities within a material. Here we introduce a general framework to quantify photon recycling which can be applied to any material. We apply our model to idealized solar cells and light-emitting diodes based on halide perovskites. By varying controllable parameters which affect photon recycling, namely, thickness, charge trapping rate, nonideal transmission at interfaces, and absorptance, we quantify the effect of each on photon recycling. In both device types, we demonstrate that maximizing absorption and emission processes remains paramount for optimizing devices, even if this is at the expense of photon recycling. Our results provide new insight into quantifying photon recycling in optoelectronic devices and demonstrate that photon recycling cannot always be seen as a beneficial process.
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Tian X, Stranks SD, You F. Life cycle energy use and environmental implications of high-performance perovskite tandem solar cells. SCIENCE ADVANCES 2020; 6:eabb0055. [PMID: 32789177 PMCID: PMC7399695 DOI: 10.1126/sciadv.abb0055] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 06/19/2020] [Indexed: 06/11/2023]
Abstract
A promising route to widespread deployment of photovoltaics is to harness inexpensive, highly-efficient tandems. We perform holistic life cycle assessments on the energy payback time, carbon footprint, and environmental impact scores for perovskite-silicon and perovskite-perovskite tandems benchmarked against state-of-the-art commercial silicon cells. The scalability of processing steps and materials in the manufacture and operation of tandems is considered. The resulting energy payback time and greenhouse gas emission factor of the all-perovskite tandem configuration are 0.35 years and 10.7 g CO2-eq/kWh, respectively, compared to 1.52 years and 24.6 g CO2-eq/kWh for the silicon benchmark. Prolonging the lifetime provides a strong technological lever for reducing the carbon footprint such that the perovskite-silicon tandem can outcompete the current benchmark on energy and environmental performance. Perovskite-perovskite tandems with flexible and lightweight form factors further improve the energy and environmental performance by around 6% and thus enhance the potential for large-scale, sustainable deployment.
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Shamsi J, Kubicki D, Anaya M, Liu Y, Ji K, Frohna K, Grey CP, Friend RH, Stranks SD. Stable Hexylphosphonate-Capped Blue-Emitting Quantum-Confined CsPbBr 3 Nanoplatelets. ACS ENERGY LETTERS 2020; 5:1900-1907. [PMID: 32566752 PMCID: PMC7296617 DOI: 10.1021/acsenergylett.0c00935] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Accepted: 05/15/2020] [Indexed: 05/05/2023]
Abstract
Quantum-confined CsPbBr3 nanoplatelets (NPLs) are extremely promising for use in low-cost blue light-emitting diodes, but their tendency to coalesce in both solution and film form, particularly under operating device conditions with injected charge-carriers, is hindering their adoption. We show that employing a short hexyl-phosphonate ligand (C6H15O3P) in a heat-up colloidal approach for pure, blue-emitting quantum-confined CsPbBr3 NPLs significantly suppresses these coalescence phenomena compared to particles capped with the typical oleyammonium ligands. The phosphonate-passivated NPL thin films exhibit photoluminescence quantum yields of ∼40% at 450 nm with exceptional ambient and thermal stability. The color purity is preserved even under continuous photoexcitation of carriers equivalent to LED current densities of ∼3.5 A/cm2. 13C, 133Cs, and 31P solid-state MAS NMR reveal the presence of phosphonate on the surface. Density functional theory calculations suggest that the enhanced stability is due to the stronger binding affinity of the phosphonate ligand compared to the ammonium ligand.
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deQuilettes DW, Laitz M, Brenes R, Dou B, Motes BT, Stranks SD, Snaith HJ, Bulović V, Ginger DS. Maximizing the external radiative efficiency of hybrid perovskite solar cells. PURE APPL CHEM 2020. [DOI: 10.1515/pac-2019-0505] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
AbstractDespite rapid advancements in power conversion efficiency in the last decade, perovskite solar cells still perform below their thermodynamic efficiency limits. Non-radiative recombination, in particular, has limited the external radiative efficiency and open circuit voltage in the highest performing devices. We review the historical progress in enhancing perovskite external radiative efficiency and determine key strategies for reaching high optoelectronic quality. Specifically, we focus on non-radiative recombination within the perovskite layer and highlight novel approaches to reduce energy losses at interfaces and through parasitic absorption. By strategically targeting defects, it is likely that the next set of record-performing devices with ultra-low voltage losses will be achieved.
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