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Hatton P, Watts MJ, Abbas A, Walls JM, Smith R, Goddard P. Chlorine activated stacking fault removal mechanism in thin film CdTe solar cells: the missing piece. Nat Commun 2021; 12:4938. [PMID: 34426582 PMCID: PMC8382740 DOI: 10.1038/s41467-021-25063-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 07/12/2021] [Indexed: 11/15/2022] Open
Abstract
The conversion efficiency of as-deposited, CdTe solar cells is poor and typically less than 5%. A CdCl2 activation treatment increases this to up to 22%. Studies have shown that stacking faults (SFs) are removed and the grain boundaries (GBs) are decorated with chlorine. Thus, SF removal and device efficiency are strongly correlated but whether this is direct or indirect has not been established. Here we explain the passivation responsible for the increase in efficiency but also crucially elucidate the associated SF removal mechanism. The effect of chlorine on a model system containing a SF and two GBs is investigated using density functional theory. The proposed SF removal mechanisms are feasible at the 400 ∘C treatment temperature. It is concluded that the efficiency increase is due to electronic effects in the GBs while SF removal is a by-product of the saturation of the GB with chlorine but is a key signal that sufficient chlorine is present for passivation to occur.
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Affiliation(s)
- Peter Hatton
- Department of Mathematical Sciences, Loughborough University, Loughborough, Leicestershire, UK
| | - Michael J Watts
- Department of Chemistry, Loughborough University, Loughborough, Leicestershire, UK
| | - Ali Abbas
- Centre for Renewable Energy Systems Technology (CREST), Loughborough University, Loughborough, Leicestershire, UK
| | - John M Walls
- Centre for Renewable Energy Systems Technology (CREST), Loughborough University, Loughborough, Leicestershire, UK
| | - Roger Smith
- Department of Mathematical Sciences, Loughborough University, Loughborough, Leicestershire, UK
| | - Pooja Goddard
- Department of Chemistry, Loughborough University, Loughborough, Leicestershire, UK.
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2
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Impact of CdCl2 Treatment in CdTe Thin Film Grown on Ultra-Thin Glass Substrate via Close Spaced Sublimation. CRYSTALS 2021. [DOI: 10.3390/cryst11040390] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In this study, close-spaced sublimation (CSS) grown cadmium telluride (CdTe) thin films with good adhesion to 100 µm thin Schott D263T ultra-thin glass (UTG) were investigated. Cadmium chloride (CdCl2) treatment in vacuum ambient was executed to enhance the film quality and optoelectrical properties of CdTe thin film. The post-deposition annealing temperature ranging from 360–420 °C was examined to improve the CdTe film quality on UTG substrate. Various characterization techniques have been used to observe the compositional, morphological, optical, as well as electrical properties. Scanning electron microscopy (SEM) verified that the CdTe morphology and grain size could be controlled via CdCl2 treatment temperature. Energy Dispersive X-Ray Analysis (EDX) results confirmed that the annealing temperature range of 375–390 °C yielded the stoichiometric CdTe films. UV-Vis analysis estimated the post-treatment bandgap energy in the range of 1.39–1.46 eV. Carrier concentration and resistivity were obtained in the order of 1013 cm−3 and 104 Ω-cm, respectively. All the experimental results established that the CdCl2 treatment temperature range of 390–405 °C might be considered as the optimum process temperature for the deposition of CdTe solar cell on UTG substrate in close-spaced sublimation (CSS) method.
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3
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Scalable ultrafast epitaxy of large-grain and single-crystal II-VI semiconductors. Sci Rep 2020; 10:2426. [PMID: 32051449 PMCID: PMC7016132 DOI: 10.1038/s41598-020-59083-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Accepted: 12/19/2019] [Indexed: 12/02/2022] Open
Abstract
A general problem for semiconductor applications is that very slow deposition on expensive single-crystal substrates yields high crystalline quality with excellent electro-optical properties, but at prohibitive costs and throughput for many applications. In contrast, rapid deposition on inexpensive substrates or nanocrystalline films yields low costs, but comparatively inferior crystallinity, carrier transport, and recombination. Here, we present methods to deposit single-crystal material at rates 2–3 orders of magnitude faster than state-of-the-art epitaxy with low-cost methods without compromising crystalline or electro-optical quality. For example, single-crystal CdTe and CdZnTe films that would take several days to grow by molecular-beam epitaxy are deposited in 8 minutes by close-spaced sublimation, yet retain the same crystalline quality measured by X-ray diffraction rocking curves. The fast deposition is coupled with effective n- and p-type in-situ doping by In, P, and As. The epitaxy can be extended to nanocrystalline substrates. For example, we recrystallize thin CdTe films on glass to deposit large grains with low defect density. The results provide new research paths for photovoltaics, detectors, infrared imaging, flexible electronics, and other applications.
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4
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Wu Y, Chen G, Yu J, Wang D, Ma C, Li C, Pennycook SJ, Yan Y, Wei SH. Hole-Induced Spontaneous Mutual Annihilation of Dislocation Pairs. J Phys Chem Lett 2019; 10:7421-7425. [PMID: 31735032 DOI: 10.1021/acs.jpclett.9b02918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Dislocations are always observed during crystal growth, and it is usually desirable to reduce the dislocation density in high-quality crystals. Here, the annihilation process of the 30° Shockley partial dislocation pairs in CdTe is studied by first-principles calculations. We found that the dislocations can glide relatively easily due to the weak local bonding. Our systematic study of the slipping mechanism of the dislocations suggests that the energy barrier for the annihilation process is low. Band structure calculations reveal that the band bending caused by the charge transfer between the two dislocation cores depends on the core-core distance. A simple linear model is proposed to describe the mechanism of formation of the dislocation pair. More importantly, we demonstrate that hole injection can affect the core structure, increase the mobility, and eventually trigger a spontaneous mutual annihilation, which could be employed as a possible facile way to reduce the dislocation density.
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Affiliation(s)
- Yelong Wu
- Key Laboratory of Nonequilibrium Synthesis and Modulation of Condensed Matter , Xian Jiaotong University, Ministry of Education , Xian , Shaanxi 710049 , China
- Shaanxi Key Laboratory of Quantum Information and Quantum Optoelectronic Devices , Xian Jiaotong University , Xian , Shaanxi 710049 , China
| | - Guangde Chen
- Key Laboratory of Nonequilibrium Synthesis and Modulation of Condensed Matter , Xian Jiaotong University, Ministry of Education , Xian , Shaanxi 710049 , China
- Shaanxi Key Laboratory of Quantum Information and Quantum Optoelectronic Devices , Xian Jiaotong University , Xian , Shaanxi 710049 , China
| | - Jinying Yu
- School of Physics , Northwest University , Xian , Shaanxi 710069 , China
| | - Dan Wang
- Key Laboratory of Nonequilibrium Synthesis and Modulation of Condensed Matter , Xian Jiaotong University, Ministry of Education , Xian , Shaanxi 710049 , China
- Shaanxi Key Laboratory of Quantum Information and Quantum Optoelectronic Devices , Xian Jiaotong University , Xian , Shaanxi 710049 , China
| | - Chao Ma
- Key Laboratory of Nonequilibrium Synthesis and Modulation of Condensed Matter , Xian Jiaotong University, Ministry of Education , Xian , Shaanxi 710049 , China
- Shaanxi Key Laboratory of Quantum Information and Quantum Optoelectronic Devices , Xian Jiaotong University , Xian , Shaanxi 710049 , China
| | - Chen Li
- Electron microscopy for Materials research (EMAT) , University Antwerpen , Groenenborgerlaan 171 , 2020 Antwerpen , Belgium
| | - Stephen J Pennycook
- Department of Materials Science and Engineering , National University of Singapore , Singapore 117575
| | - Yanfa Yan
- Department of Physics and Astronomy , The University of Toledo , Toledo , Ohio 43606 , United States
| | - Su-Huai Wei
- Beijing Computational Science Research Center , Beijing 100193 , China
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5
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Li C, Habler G, Griffiths T, Rečnik A, Jeřábek P, Götze LC, Mangler C, Pennycook TJ, Meyer J, Abart R. Structure evolution of h.c.p./c.c.p. metal oxide interfaces in solid-state reactions. ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES 2018; 74:466-480. [PMID: 30182934 DOI: 10.1107/s205327331800757x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2017] [Accepted: 05/20/2018] [Indexed: 11/10/2022]
Abstract
The structure of crystalline interfaces plays an important role in solid-state reactions. The Al2O3/MgAl2O4/MgO system provides an ideal model system for investigating the mechanisms underlying the migration of interfaces during interface reaction. MgAl2O4 layers have been grown between Al2O3 and MgO, and the atomic structure of Al2O3/MgAl2O4 interfaces at different growth stages was characterized using aberration-corrected scanning transmission electron microscopy. The oxygen sublattice transforms from hexagonal close-packed (h.c.p.) stacking in Al2O3 to cubic close-packed (c.c.p.) stacking in MgAl2O4. Partial dislocations associated with steps are observed at the interface. At the reaction-controlled early growth stages, such partial dislocations coexist with the edge dislocations. However, at the diffusion-controlled late growth stages, such partial dislocations are dominant. The observed structures indicate that progression of the Al2O3/MgAl2O4 interface into Al2O3 is accomplished by the glide of partial dislocations accompanied by the exchange of Al3+ and Mg2+ cations. The interface migration may be envisaged as a plane-by-plane zipper-like motion, which repeats along the interface facilitating its propagation. MgAl2O4 grains can adopt two crystallographic orientations with a twinning orientation relationship, and grow by dislocations gliding in opposite directions. Where the oppositely propagating partial dislocations and interface steps meet, interlinked twin boundaries and incoherent Σ3 grain boundaries form. The newly grown MgAl2O4 grains compete with each other, leading to a growth selection and successive coarsening of the MgAl2O4 grains. This understanding could help to interpret the interface reaction or phase transformation of a wide range of materials that exhibit a similar h.c.p./c.c.p. transition.
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Affiliation(s)
- C Li
- Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, 1090, Austria
| | - G Habler
- Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, 1090, Austria
| | - T Griffiths
- Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, 1090, Austria
| | - A Rečnik
- Department for Nanostructured Materials, Joǽef Stefan Institute, Jamova cesta 39, Ljubljana, SI-1000, Slovenia
| | - P Jeřábek
- Institute of Petrology and Structural Geology, Faculty of Science, Charles University, Albertov 6, Prague, 12843, Czech Republic
| | - L C Götze
- Institute of Geological Sciences, Freie Universität Berlin, Malteserstrasse 74-100, Berlin, 12249, Germany
| | - C Mangler
- Faculty of Physics, University of Vienna, Boltzmanngasse 5, Vienna, 1090, Austria
| | - T J Pennycook
- Stuttgart Center for Electron Microscopy, Max Planck Institute for Solid State Research, Heisenbergstrasse 1, Stuttgart, 70569, Germany
| | - J Meyer
- Faculty of Physics, University of Vienna, Boltzmanngasse 5, Vienna, 1090, Austria
| | - R Abart
- Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, 1090, Austria
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6
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Fernando JFS, Zhang C, Firestein KL, Golberg D. Optical and Optoelectronic Property Analysis of Nanomaterials inside Transmission Electron Microscope. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2017; 13. [PMID: 28902975 DOI: 10.1002/smll.201701564] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Revised: 07/11/2017] [Indexed: 05/10/2023]
Abstract
In situ transmission electron microscopy (TEM) allows one to investigate nanostructures at high spatial resolution in response to external stimuli, such as heat, electrical current, mechanical force and light. This review exclusively focuses on the optical, optoelectronic and photocatalytic studies inside TEM. With the development of TEMs and specialized TEM holders that include in situ illumination and light collection optics, it is possible to perform optical spectroscopies and diverse optoelectronic experiments inside TEM with simultaneous high resolution imaging of nanostructures. Optical TEM holders combining the capability of a scanning tunneling microscopy probe have enabled nanomaterial bending/stretching and electrical measurements in tandem with illumination. Hence, deep insights into the optoelectronic property versus true structure and its dynamics could be established at the nanometer-range precision thus evaluating the suitability of a nanostructure for advanced light driven technologies. This report highlights systems for in situ illumination of TEM samples and recent research work based on the relevant methods, including nanomaterial cathodoluminescence, photoluminescence, photocatalysis, photodeposition, photoconductivity and piezophototronics.
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Affiliation(s)
- Joseph F S Fernando
- School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
| | - Chao Zhang
- School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
| | - Konstantin L Firestein
- School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
- National University of Science and Technology "MISIS", Leninsky prospect 4, Moscow, 119049, Russia
| | - Dmitri Golberg
- School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
- World Premier International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki, 3050044, Japan
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7
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The impact of STEM aberration correction on materials science. Ultramicroscopy 2017; 180:22-33. [DOI: 10.1016/j.ultramic.2017.03.020] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Revised: 03/04/2017] [Accepted: 03/16/2017] [Indexed: 11/22/2022]
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8
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Gruber J, Zhou XW, Jones RE, Lee SR, Tucker GJ. Molecular dynamics studies of defect formation during heteroepitaxial growth of InGaN alloys on (0001) GaN surfaces. JOURNAL OF APPLIED PHYSICS 2017; 121:195301. [PMID: 28611488 PMCID: PMC5432374 DOI: 10.1063/1.4983066] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 04/20/2017] [Indexed: 05/14/2023]
Abstract
We investigate the formation of extended defects during molecular-dynamics (MD) simulations of GaN and InGaN growth on (0001) and ([Formula: see text]) wurtzite-GaN surfaces. The simulated growths are conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN surface; we apply time-and-position-dependent boundary constraints that vary the ensemble treatments of the vapor-phase, the near-surface solid-phase, and the bulk-like regions of the growing layer. The simulations employ newly optimized Stillinger-Weber In-Ga-N-system potentials, wherein multiple binary and ternary structures are included in the underlying density-functional-theory training sets, allowing improved treatment of In-Ga-related atomic interactions. To examine the effect of growth conditions, we study a matrix of >30 different MD-growth simulations for a range of In x Ga 1-x N-alloy compositions (0 ≤ x ≤ 0.4) and homologous growth temperatures [0.50 ≤ T/T*m (x) ≤ 0.90], where T*m (x) is the simulated melting point. Growths conducted on polar (0001) GaN substrates exhibit the formation of various extended defects including stacking faults/polymorphism, associated domain boundaries, surface roughness, dislocations, and voids. In contrast, selected growths conducted on semi-polar ([Formula: see text]) GaN, where the wurtzite-phase stacking sequence is revealed at the surface, exhibit the formation of far fewer stacking faults. We discuss variations in the defect formation with the MD growth conditions, and we compare the resulting simulated films to existing experimental observations in InGaN/GaN. While the palette of defects observed by MD closely resembles those observed in the past experiments, further work is needed to achieve truly predictive large-scale simulations of InGaN/GaN crystal growth using MD methodologies.
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Affiliation(s)
| | - X W Zhou
- Mechanics of Materials Department, Sandia National Laboratories, Livermore, California 94550, USA
| | - R E Jones
- Mechanics of Materials Department, Sandia National Laboratories, Livermore, California 94550, USA
| | - S R Lee
- Advanced Materials Sciences Department, Sandia National Laboratories, Albuquerque, New Mexico 87123, USA
| | - G J Tucker
- Materials Science and Engineering Department, Drexel University, Philadelphia, Pennsylvania 19104, USA
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9
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Kutes Y, Luria J, Sun Y, Moore A, Aguirre BA, Cruz-Campa JL, Aindow M, Zubia D, Huey BD. Ion-damage-free planarization or shallow angle sectioning of solar cells for mapping grain orientation and nanoscale photovoltaic properties. NANOTECHNOLOGY 2017; 28:185705. [PMID: 28397709 DOI: 10.1088/1361-6528/aa67c2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Ion beam milling is the most common modern method for preparing specific features for microscopic analysis, even though concomitant ion implantation and amorphization remain persistent challenges, particularly as they often modify materials properties of interest. Atomic force microscopy (AFM), on the other hand, can mechanically mill specific nanoscale regions in plan-view without chemical or high energy ion damage, due to its resolution, directionality, and fine load control. As an example, AFM-nanomilling (AFM-NM) is implemented for top-down planarization of polycrystalline CdTe thin film solar cells, with a resulting decrease in the root mean square (RMS) roughness by an order of magnitude, even better than for a low incidence FIB polished surface. Subsequent AFM-based property maps reveal a substantially stronger contrast, in this case of the short-circuit current or open circuit voltage during light exposure. Electron back scattering diffraction (EBSD) imaging also becomes possible upon AFM-NM, enabling direct correlations between the local materials properties and the polycrystalline microstructure. Smooth shallow-angle cross-sections are demonstrated as well, based on targeted oblique milling. As expected, this reveals a gradual decrease in the average short-circuit current and maximum power as the underlying CdS and electrode layers are approached, but a relatively consistent open-circuit voltage through the diminishing thickness of the CdTe absorber. AFM-based nanomilling is therefore a powerful tool for material characterization, uniquely providing ion-damage free, selective area, planar smoothing or low-angle sectioning of specimens while preserving their functionality. This enables novel, co-located advanced AFM measurements, EBSD analysis, and investigations by related techniques that are otherwise hindered by surface morphology or surface damage.
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Affiliation(s)
- Yasemin Kutes
- Department of Materials Science and Engineering, University of Connecticut, Storrs, CT, United States of America
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10
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Arroyo Rojas Dasilva Y, Kozak R, Erni R, Rossell MD. Structural defects in cubic semiconductors characterized by aberration-corrected scanning transmission electron microscopy. Ultramicroscopy 2016; 176:11-22. [PMID: 27838069 DOI: 10.1016/j.ultramic.2016.09.015] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 09/23/2016] [Accepted: 09/25/2016] [Indexed: 11/29/2022]
Abstract
The development of new electro-optical devices and the realization of novel types of transistors require a profound understanding of the structural characteristics of new semiconductor heterostructures. This article provides a concise review about structural defects which occur in semiconductor heterostructures on the basis of micro-patterned Si substrates. In particular, one- and two-dimensional crystal defects are being discussed which are due to the plastic relaxation of epitaxial strain caused by the misfit of crystal lattices. Besides a few selected examples from literature, we treat in particular crystal defects occurring in GaAs/Si, Ge/Si and β-SiC/Si structures which are studied by high-resolution annular dark-field scanning transmission electron microscopy. The relevance of this article is twofold; firstly, it should provide a collection of data which are of help for the identification and characterization of defects in cubic semiconductors by means of atomic-resolution imaging, and secondly, the experimental data shall provide a basis for advancing the understanding of device characteristics with the aid of theoretical modelling by considering the defective nature of strained semiconductor heterostructures.
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Affiliation(s)
- Yadira Arroyo Rojas Dasilva
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland
| | - Roksolana Kozak
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland
| | - Rolf Erni
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland
| | - Marta D Rossell
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland.
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11
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Major JD, Al Turkestani M, Bowen L, Brossard M, Li C, Lagoudakis P, Pennycook SJ, Phillips LJ, Treharne RE, Durose K. In-depth analysis of chloride treatments for thin-film CdTe solar cells. Nat Commun 2016; 7:13231. [PMID: 27775037 PMCID: PMC5078995 DOI: 10.1038/ncomms13231] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Accepted: 09/14/2016] [Indexed: 11/09/2022] Open
Abstract
CdTe thin-film solar cells are now the main industrially established alternative to silicon-based photovoltaics. These cells remain reliant on the so-called chloride activation step in order to achieve high conversion efficiencies. Here, by comparison of effective and ineffective chloride treatments, we show the main role of the chloride process to be the modification of grain boundaries through chlorine accumulation, which leads an increase in the carrier lifetime. It is also demonstrated that while improvements in fill factor and short circuit current may be achieved through use of the ineffective chlorides, or indeed simple air annealing, voltage improvement is linked directly to chlorine incorporation at the grain boundaries. This suggests that focus on improved or more controlled grain boundary treatments may provide a route to achieving higher cell voltages and thus efficiencies.
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Affiliation(s)
- J D Major
- Stephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool L69 7ZF, UK
| | - M Al Turkestani
- Department of Physics, Umm Al-Qura University, KSA, Mecca Al Taif Road, Mecca 24382, Saudi Arabia
| | - L Bowen
- Department of Physics, G.J. Russell Microscopy Facility, Durham University, South Road, Durham DH1 3LE, UK
| | - M Brossard
- University of Southampton, School of Physics &Astronomy, Southampton, Hants SO17 1BJ, UK.,Centre for Photonics and Quantum Materials, Skolkovo Institute of Science and Technology, Moscow 143026, Russia
| | - C Li
- Materials Science and Technology Division, Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, Tennessee 37831, USA
| | - P Lagoudakis
- University of Southampton, School of Physics &Astronomy, Southampton, Hants SO17 1BJ, UK.,Centre for Photonics and Quantum Materials, Skolkovo Institute of Science and Technology, Moscow 143026, Russia
| | - S J Pennycook
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117576, Singapore
| | - L J Phillips
- Stephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool L69 7ZF, UK
| | - R E Treharne
- Stephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool L69 7ZF, UK
| | - K Durose
- Stephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool L69 7ZF, UK
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12
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Structural and compositional dependence of the CdTexSe1-x alloy layer photoactivity in CdTe-based solar cells. Nat Commun 2016; 7:12537. [PMID: 27460872 PMCID: PMC4974465 DOI: 10.1038/ncomms12537] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Accepted: 07/12/2016] [Indexed: 11/16/2022] Open
Abstract
The published external quantum efficiency data of the world-record CdTe solar cell suggests that the device uses bandgap engineering, most likely with a CdTexSe1−x alloy layer to increase the short-circuit current and overall device efficiency. Here atom probe tomography, transmission electron microscopy and electron beam-induced current are used to clarify the dependence of Se content on the photoactive properties of CdTexSe1−x alloy layers in bandgap-graded CdTe solar cells. Four solar cells were prepared with 50, 100, 200 and 400 nm-thick CdSe layers to reveal the formation, growth, composition, structure and photoactivity of the CdTexSe1−x alloy with respect to the degree of Se diffusion. The results show that the CdTexSe1−x layer photoactivity is highly dependent on the crystalline structure of the alloy (zincblende versus wurtzite), which is also dependent on the Se and Te concentrations. Using a CdTexSe1−x alloy in CdTe solar cells leads to better performances. Here, Poplawsky et al. show that the photoactive properties of the alloy depend on its chemical composition and structural properties, and derive a phase diagram to further optimize alloy growth for photovoltaic devices.
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13
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Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface. Sci Rep 2016; 6:27009. [PMID: 27255415 PMCID: PMC4891715 DOI: 10.1038/srep27009] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 05/12/2016] [Indexed: 12/01/2022] Open
Abstract
Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1–10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis.
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14
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Li H, Liu XX, Lin YS, Yang B, Du ZM. Enhanced electrical properties at boundaries including twin boundaries of polycrystalline CdTe thin-film solar cells. Phys Chem Chem Phys 2015; 17:11150-5. [DOI: 10.1039/c5cp00564g] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The effect of grain boundaries (GBs), in particular twin boundaries (TBs), on CdTe polycrystalline thin films is studied by conductive atomic force microscopy (C-AFM), electron-beam-induced current (EBIC), scanning Kelvin probe microscopy (SKPM), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (STEM).
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Affiliation(s)
- H. Li
- The Key Laboratory of Solar Thermal Energy and Photovoltaic System
- Institute of Electrical Engineering
- Chinese Academy of Sciences
- Beijing 100190
- China
| | - X. X. Liu
- The Key Laboratory of Solar Thermal Energy and Photovoltaic System
- Institute of Electrical Engineering
- Chinese Academy of Sciences
- Beijing 100190
- China
| | - Y. S. Lin
- Institute of Electrical Engineering
- Chinese Academy of Sciences
- Beijing 100190
- China
| | - B. Yang
- The Key Laboratory of Solar Thermal Energy and Photovoltaic System
- Institute of Electrical Engineering
- Chinese Academy of Sciences
- Beijing 100190
- China
| | - Z. M. Du
- The Key Laboratory of Solar Thermal Energy and Photovoltaic System
- Institute of Electrical Engineering
- Chinese Academy of Sciences
- Beijing 100190
- China
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Phillips PJ, Paulauskas T, Rowlands N, Nicholls AW, Low KB, Bhadare S, Klie RF. A new silicon drift detector for high spatial resolution STEM-XEDS: performance and applications. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2014; 20:1046-1052. [PMID: 25410601 DOI: 10.1017/s1431927614001639] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A newly designed, 100 mm2, silicon drift detector has been installed on an aberration-corrected scanning transmission electron microscope equipped with an ultra-high resolution pole piece, without requiring column modifications. With its unique, windowless design, the detector's active region is in close proximity to the sample, resulting in a dramatic increase in count rate, while demonstrating an increased sensitivity to low energy X-rays and a muted tilt dependence. Numerous examples of X-ray energy dispersive spectrometry are presented on relevant materials such as Al x Ga1-x N nanowires, perovskite oxides, and polycrystalline CdTe thin films, across both varying length scales and accelerating voltages.
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Affiliation(s)
- Patrick J Phillips
- 1Department of Physics,University of Illinois at Chicago,845 W Taylor Street,Chicago,IL 60607,USA
| | - Tadas Paulauskas
- 1Department of Physics,University of Illinois at Chicago,845 W Taylor Street,Chicago,IL 60607,USA
| | - Neil Rowlands
- 2Oxford Instruments NanoAnalysis,Halifax Road,High Wycombe,HP12 3SE,UK
| | - Alan W Nicholls
- 3Research Resources Center,University of Illinois at Chicago,845 W Taylor Street,Chicago,IL 60607,USA
| | - Ke-Bin Low
- 4BASF,25 Middlesex/Essex Turnpike,Iselin,NJ 08830,USA
| | - Santokh Bhadare
- 2Oxford Instruments NanoAnalysis,Halifax Road,High Wycombe,HP12 3SE,UK
| | - Robert F Klie
- 1Department of Physics,University of Illinois at Chicago,845 W Taylor Street,Chicago,IL 60607,USA
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16
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Li C, Wu Y, Poplawsky J, Pennycook TJ, Paudel N, Yin W, Haigh SJ, Oxley MP, Lupini AR, Al-Jassim M, Pennycook SJ, Yan Y. Grain-boundary-enhanced carrier collection in CdTe solar cells. PHYSICAL REVIEW LETTERS 2014; 112:156103. [PMID: 24785058 DOI: 10.1103/physrevlett.112.156103] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2013] [Indexed: 05/28/2023]
Abstract
When CdTe solar cells are doped with Cl, the grain boundaries no longer act as recombination centers but actively contribute to carrier collection efficiency. The physical origin of this remarkable effect has been determined through a combination of aberration-corrected scanning transmission electron microscopy, electron energy loss spectroscopy, and first-principles theory. Cl substitutes for a large proportion of the Te atoms within a few unit cells of the grain boundaries. Density functional calculations reveal the mechanism, and further indicate the grain boundaries are inverted to n type, establishing local p-n junctions which assist electron-hole pair separation. The mechanism is electrostatic, and hence independent of the geometry of the boundary, thereby explaining the universally high collection efficiency of Cl-doped CdTe solar cells.
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Affiliation(s)
- Chen Li
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, USA and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Yelong Wu
- Department of Physics and Astronomy, The University of Toledo, Toledo, Ohio 43606, USA
| | - Jonathan Poplawsky
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA and Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Timothy J Pennycook
- Department of Materials, University of Oxford, Oxford OX13PH, United Kingdom and SuperSTEM Laboratory, Daresbury WA44AD, United Kingdom
| | - Naba Paudel
- Department of Physics and Astronomy, The University of Toledo, Toledo, Ohio 43606, USA
| | - Wanjian Yin
- Department of Physics and Astronomy, The University of Toledo, Toledo, Ohio 43606, USA
| | - Sarah J Haigh
- School of Materials, University of Manchester, Manchester M139PL, United Kingdom
| | - Mark P Oxley
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA and Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, USA
| | - Andrew R Lupini
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Mowafak Al-Jassim
- The Measurements and Characterization Group, National Renewable Energy Laboratory, Golden, Colorado 80401, USA
| | - Stephen J Pennycook
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Yanfa Yan
- Department of Physics and Astronomy, The University of Toledo, Toledo, Ohio 43606, USA
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17
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Ng A, Poplawsky JD, Li C, Pennycook SJ, Rosenthal SJ. Direct Electronic Property Imaging of a Nanocrystal-Based Photovoltaic Device by Electron Beam-Induced Current via Scanning Electron Microscopy. J Phys Chem Lett 2014; 5:856-860. [PMID: 26274078 DOI: 10.1021/jz402752k] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Scanning electron microscopy (SEM) electron beam-induced current (EBIC) studies were performed on the cross-section of a nanocrystal-based hybrid bulk heterojunction photovoltaic device. Using these techniques, the short circuit carrier collection efficiencies are mapped with a better than 100 nm resolution. Electronically deficient and proficient regions within the photoactive layer are determined. The results show that only a fraction of the CdSe nanorod:P3HT layer (P3HT = poly-3(hexylthiophene)) at the Al cathode interface shows primary collection of charged carriers, in which the photoactivity decreases exponentially away from the interface. The recombination losses of the photoactive layer away from this interface prove that the limiting factor of the device is the inability for electrons to percolate between nanoparticles; to alleviate this problem, an interparticle network that conducts the electrons from one nanorod to the next must be established. Furthermore, the EBIC technique applied to the nanocrystalline device used in this study is the first measurement of its kind and can be applied toward other similar architectures.
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Affiliation(s)
- Amy Ng
- †Department of Chemistry, Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Jonathan D Poplawsky
- ‡Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
- §Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, 37996, United States
| | - Chen Li
- †Department of Chemistry, Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Nashville, Tennessee 37235, United States
- ‡Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Stephen J Pennycook
- ‡Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
- §Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, 37996, United States
| | - Sandra J Rosenthal
- †Department of Chemistry, Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Nashville, Tennessee 37235, United States
- ‡Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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18
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Li L, Gan Z, McCartney MR, Liang H, Yu H, Gao Y, Wang J, Smith DJ. Atomic configurations at InAs partial dislocation cores associated with Z-shape faulted dipoles. Sci Rep 2013; 3:3229. [PMID: 24231692 PMCID: PMC3828569 DOI: 10.1038/srep03229] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2013] [Accepted: 10/31/2013] [Indexed: 11/09/2022] Open
Abstract
The atomic arrangements of two types of InAs dislocation cores associated by a Z-shape faulted dipole are observed directly by aberration-corrected high-angle annular-dark-field imaging. Single unpaired columns of different atoms in a matrix of dumbbells are clearly resolved, with observable variations of bonding lengths due to excess Coulomb force from bare ions at the dislocation core. The corresponding geometric phase analysis provides confirmation that the dislocation cores serve as origins of strain field inversion while stacking faults maintain the existing strain status.
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Affiliation(s)
- Luying Li
- 1] Center for Nanoscale Characterization and Devices, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China [2] Department of Physics, Arizona State University, Tempe, Arizona 85287, USA
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