@article{8d8d976287f243b7809b124ed26640d4,
title = "Strain Mapping of CdTe Grains in Photovoltaic Devices",
abstract = "Strain within grains and at grain boundaries (GBs) in polycrystalline thin-film absorber layers limits the overall performance because of higher defect concentrations and band fluctuations. However, the nanoscale strain distribution in operational devices is not easily accessible using standard methods. X-ray nanodiffraction offers the unique possibility to evaluate the strain or lattice spacing at nanoscale resolution. Furthermore, the combination of nanodiffraction with additional techniques in the framework of multimodal scanning X-ray microscopy enables the direct correlation of the strain with material and device parameters such as the elemental distribution or local performance. This approach is applied for the investigation of the strain distribution in CdTe grains in fully operational photovoltaic solar cells. It is found that the lattice spacing in the (111) direction remains fairly constant in the grain cores but systematically decreases at the GBs. The lower strain at GBs is accompanied by an increase of the total tilt. These observations are both compatible with the inhomogeneous incorporation of smaller atoms into the lattice, and local stress induced by neighboring grains.",
keywords = "CdTe, X-ray, X-ray beam induced current (XBIC), X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray microscopy, multimodal, nanodiffraction, photovoltaic, solar cells, strain",
author = "Irene Calvo-Almazan and Xiaojing Huang and Hanfei Yan and Evgeny Nazaretski and Chu, {Yong S.} and Hruszkewycz, {Stephan O.} and Stuckelberger, {Michael Elias} and Ulvestad, {Andrew P.} and Eric Colegrove and Tursun Ablekim and Holt, {Martin V.} and Hill, {Megan O.} and Siddharth Maddali and Lauhon, {Lincoln J.} and Bertoni, {Mariana I.}",
note = "Funding Information: Dr. Lauhon was the recipient of an NSF CAREER Award, a Sloan Fellowship in Chemistry, and a Camille Dreyfus Teacher Scholar Award. In collaborative endeavors, he leads IRG-1 in the Northwestern Materials Research Center, and serves on the Board of Directors for the Materials Research Society. Funding Information: the Hard X-ray Nanoprobe (HXN) Beamline at 3-ID of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Funding Information: Manuscript received June 17, 2019; revised August 22, 2019; accepted September 14, 2019. Date of publication October 8, 2019; date of current version October 28, 2019. X-ray nanodiffraction experiments and data reduction was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences (BES), Materials Science and Engineering Division. This research used Funding Information: Contract322DE-AC02-06CH11357.TheworkofM.O.HillwassupportedinScienceUserFacilitysupportedbytheU.S.DOE,OfficeofScience,BES,under Grain boundaries (GBs) in CdTe are known to limit the perfor- part by the National Science Foundation under Grant DMR-1611341 and in part mance as a result of increased recombination. Recrystallization bytheNationalScienceFoundationGraduateResearchFellowshipProgram. and passivation during CdCl2 treatments can reduce this GB underGrantDMR-1611341.(Correspondingauthor:MichaelE.Stuckelberger.)TheworkofL.J.LauhonwassupportedbytheNationalScienceFoundation recombination but not eliminate it entirely [2]–[7]. The extent to I. Calvo-Almaz{\'a}n, S. Maddali, and S. O. Hruszkewycz are with the Mate-which lattice strain and stress play a role with respect to impurity rialsScienceDivision,ArgonneNationalLaboratory,Lemont,IL60439USA segregation, diffusion, and ultimately charge-carrier kinetics is A.P.UlvestadiswithMaterialsScienceDivision,ArgonneNationalLabo-(e-mail:ialmazn@anl.gov;smaddali@anl.gov;shrus@anl.gov). still being investigated. ratory, Lemont, IL 60439 USA, and also with Tesla, Palo Alto, CA 94306 USA At a macroscopic scale, early work studied lattice strain (the (e-mail:andrew.ulvestad@gmail.com). average change of the lattice parameter) using X-ray diffrac-Golden,CO80401USA(e-mail:eric.colegrove@nrel.gov;tursun.ablekim@E.ColegroveandT.AblekimarewithNationalRenewableEnergyLaboratory, tion (XRD) and optical methods [8]–[10]. Strain was observed nrel.gov). to contribute to band tails, and recrystallization during CdCl2 M.V.HoltiswiththeCenterforNanoscaleMaterials,ArgonneNational treatments has been shown to relax this strain [10]. At the sub-M.O.HillandL.J.LauhonarewiththeDepartmentofMaterialsScienceLaboratory,Lemont,IL60439USA(e-mail:mvholt@anl.gov). nanometer scale, local lattice distortions, also called microscopic and Engineering, Northwestern University, Evanston, IL 60208 USA (e-mail: strain, have been studied at interfaces, and individual defects meganhill2020@u.northwestern.edu;lauhon@northwestern.edu). have been observed using transmission electron microscopes ergyEngineering,ArizonaStateUniversity,Tempe,AZ85287USA(e-mail:M.I. Bertoni iswith theDepartmentofElectricalComputerandEn- [11], [12]. In conjunction with density functional theory calcu- bertoni@asu.edu). lations, lattice distortions at dislocations were shown to produce X.Huang,H.Yan,E.Nazaretski,andY.S.ChuarewithNationalSynchrotron recombination-active midgap states that Cl can help to mitigate mail:xjhuang@bnl.gov;hyan@bnl.gov;enazaretski@bnl.gov;ychu@bnl.gov).LightSourceII,BrookhavenNationalLaboratory,Upton,NY11973USA(e- [12]. Within large grains of very thick (>200 μm) CdTe material, M. E. Stuckelberger is with Deutsches Elektronen-Synchrotron, Hamburg nonuniformities have been examined using a combination of 22607,Germany(e-mail:michael.stuckelberger@desy.de). electron backscattered diffraction, electron-beam-induced cur-athttp://ieeexplore.ieee.org.Colorversionsofoneormoreofthefiguresinthisarticleareavailableonline rent, cathodoluminescence, and Laue XRD. The origin of this Digital Object Identifier 10.1109/JPHOTOV.2019.2942487 nonuniformity was speculated to result from film and grain 2156-3381 {\textcopyright} 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. Publisher Copyright: {\textcopyright} 2011-2012 IEEE.",
year = "2019",
month = nov,
doi = "10.1109/JPHOTOV.2019.2942487",
language = "English (US)",
volume = "9",
pages = "1790--1799",
journal = "IEEE Journal of Photovoltaics",
issn = "2156-3381",
publisher = "IEEE Electron Devices Society",
number = "6",
}
