Two-Dimensional Cadmium Chloride Nanosheets in Cadmium

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Two Dimensional Cadmium Chloride Nanosheets in Cadmium Telluride Solar Cells Craig L Perkins, Carolyn Beall, Matthew O. Reese, and TM Barnes ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 12 May 2017 Downloaded from http://pubs.acs.org on May 14, 2017

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Figure 1. In (a), a schematic of the device stack prior to cleaving. Panel (b) shows XPS spectra of both sides of the cleave. Auger micrographs of the CdS side are shown in (c). Panel (d) shows an AFM image of the CdS side. Image is 20 microns across.

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Figure 2. XPS sputter depth profile from the CdS side of the interface. 106x99mm (300 x 300 DPI)


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Figure 3. XPS spectra showing effects of water washing on line-shapes (Cd and S) and on intensities (Cl 2p and O 1s). Cd and S spectra are normalized to maximum peak height.



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Figure 4. Angle-resolved XPS data from the SnO2 side (a) and the CdS side (b). Panel (c) shows the strucure of CdCl2 for comparison. Panel (d) shows a schematic of the SnO2-CdS interface.


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Two dimensional cadmium chloride nanosheets in cadmium telluride solar cells Craig L. Perkins, Carolyn Beall, Matthew O. Reese, and Teresa M. Barnes National Renewable Energy Laboratory, Golden CO 80401 USA Keywords: cadmium telluride, cadmium chloride, solar cells, nanosheets, XPS Abstract In this study we make use of a liquid nitrogen-based thermomechanical cleavage technique and a surface analysis cluster tool to probe in detail the tin oxide/emitter interface at the front of completed CdTe solar cells. We show that this thermomechanical cleavage occurs within a few angstroms of the SnO2/emitter interface. An unexpectedly high concentration of chlorine at this interface, ~20%, was determined from a calculation that assumed a uniform chlorine distribution. Angle-resolved X-ray photoelectron spectroscopy was used to further probe the structure of the chlorine containing layer, revealing that both sides of the cleave location are covered by one third of a unit cell of pure CdCl2, a thickness corresponding to about one Cl-Cd-Cl molecular layer. We interpret this result in the context of CdCl2 being a true layered material similar to transition metal dichalcogenides. Exposing cleaved surfaces to water shows that this Cl-Cd-Cl trilayer is soluble, raising questions pertinent to cell reliability. Our work provides new and unanticipated details about the structure and chemistry of front surface interfaces and should prove important to improving materials, processes, and reliability of next generation CdTe-based solar cells. Introduction Despite their development into high efficiency (~19%) commercially available photovoltaic panels, CdTe solar cells with superstrate architectures have a poorly understood, complex front surface formed via interdiffusion of the CdS-based emitter and the CdTe absorber.1 Interfaces in this region of the cell are difficult to probe by standard surface analytical methods because they are bound by glass on one side and microns of CdTe on the other. Post-growth processing with CdCl2 and for back contacting is likely to further change these buried interfaces, making the traditional scheme of interface analysis – interleaved depositions and analyses – impractical. Yet these front interfaces are important. Recent modeling shows that recombination at the cell front will be increasingly critical to cell efficiency as doping levels are improved from ~1014 cm-3 to 1016 cm-3. For example, Burst et al. have demonstrated that reducing the CdS/CdTe interface recombination velocity (S) to ~100 cm/s from 106 cm/s can increase the open circuit voltage of these devices to over one volt.2 We note that unpassivated CdTe surfaces typically have S values in the range of 105 to 106 cm/s.3 Efforts to understand the nanoscale chemistry and structure of CdTe solar cells stretch back years and have relied on a variety of characterization techniques. A recent review of CdTe grain boundaries by Major highlights the fact that electron microscopy and its many variants have played a key role in this field.4 Low to medium resolution electron microscopy has enjoyed wide utility. High spatial resolution electron microscopy studies are hampered though by the fact that sample preparation techniques such as ion milling and mechanical polishing can change the structure and composition of the materials being 1 ACS Paragon Plus Environment


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studied, sometimes making atomic scale details difficult to obtain and to interpret. Focused ion beams for example are known to cause strain relaxation,5 changes in crystallinity, composition, and atomic scale rearrangements.6,7 In contrast, mechanical cleaving is one of the best ways to access a buried surface without perturbing a crystal’s properties.7–10 Surface analysis methods such as angle-resolved X-ray photoelectron spectroscopy (ARXPS), low energy ion scattering (LEIS), and static secondary ion mass spectrometry (SSIMS) can also reveal atomic-scale details about semiconductor structures. One challenge to making use of both the advantages of mechanical cleaving and one of these surface analysis methods is that the analysis methods typically have high spatial resolution along only one dimension (normal to the surface), and cleaving multilayered thin film samples almost always yields cross sections rather than sections coplanar with the sample surface. In our recent efforts to better understand and improve the properties of the front interfaces in CdTe solar cells, we have relied on a simple improvement of a cleavage technique first developed in 2002 by Albin and coworkers.11 In their early work, Albin and coworkers glued a glass plate to the back contact of a finished CdTe solar cell and then physically pulled apart the resulting stack. Although this worked in some cases, separation of these devices was not laterally uniform and the process suffered from poor yields. More recently, Meysing and coworkers realized that by plunging this same structure into liquid nitrogen, devices separated cleanly near the TCO-CdS interface, making it amenable to being probed by various surface analysis methods.12 Expanding on the prior work of Albin and Meysing, we have used Auger electron spectroscopy and ARXPS combined with the LN2-based thermo-mechanical cleavage process to examine a series of high efficiency CdTe solar cells with the superstrate architecture. It is shown that standard CdCl2 treatment of CdTe solar cells causes the formation of two dimensional CdCl2 nanosheets at the tin oxide/cadmium sulfide interface. We assert that viewing CdCl2 as a true two dimensional layered material analogous to transition metal dichalcogenides provides natural explanations for heretofore unexplained phenomena including why the thermo-mechanical cleavage occurs where it does, why different chlorine treatments yield similarly passivated grain boundaries, and also provides guidance for improved post-growth processing of CdTe solar cells. Experimental Superstrate architecture CdTe devices were produced as described previously using sputtered CdS:O emitters, vapor-phase CdCl2 treatment, and Cu/Au back contacts.12 Without anti-reflection coatings, device efficiencies ranged from 14.5 ± 0.5% with open circuit voltages of 835 ± 15 mV, short circuit currents of 23.5 ± 0.2 mA/cm2, and fill factors of 73.5 ± 2%. XPS and AES experiments were conducted in a home-built cluster tool that has been previously described.13 Using a UHV-compatible epoxy (Hysol 1C), devices were affixed to clean glass coupons and allowed to cure overnight (Figure 1a). In a glovebox attached to our cluster tool, epoxied samples were immersed in a bath of liquid nitrogen where they spontaneously cleaved. Each half was then withdrawn from the LN2 bath into a stream of dry nitrogen gas until it reached room temperature. Samples were loaded directly into the UHV transport system and into the XPS such that air exposure was avoided.

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Sputter depth profiling was performed using a 3 kV Ar+ beam while monitoring the Cd 3d5/2, Te 3d5/2, S 2s, O 1s, and Cl 2p peaks using a pass energy of 58.7 eV. Data were processed with PHI MultiPak v9.6 using standard elemental sensitivity factors. Angle-resolved XPS data were taken using Mg Al Kα radiation, a pass energy of 58.7 eV, and with a lens mode that corresponds to an acceptance angle of ± 2°. Thicknesses for CdCl2 were obtained using

ln 1

∞ ∞

Y,

(1)

where is CdCl2 layer thickness, is effective attenuation length, is areal intensity from ∞ is the Cl 2p intensity from a thick film of pure CdCl2, the Cl 2p transition from a thin over-layer,

∞ is the attenuated intensity from substrate signals (either S 2s or Sn 3d5/2), and is the intensity from the substrate having no chloride over-layer. Effective attenuation lengths were obtained using the NIST EAL database.14 Least squares fits made to plots of Y versus secant yielded lines with slopes of

, allowing straightforward determination of CdCl2 layer thicknesses.

High resolution XPS spectra were taken at normal take-off angle using monochromatic Al Kα radiation,

Figure 1. In (a), a schematic of the device stack prior to cleaving. Panel (b) shows XPS spectra of both sides of the cleave. Auger micrographs of the CdS side are shown in (c). Panel (d) shows an AFM image of the CdS side. Image is 20 microns across.


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with a pass energy of 29.34 eV, and in angle integrating lens mode (±7°). Auger electron spectroscopy was performed using a 5 kV, 20 nA primary beam. Removal of CdCl2 was accomplished using brief (10 s) exposure to room temperature vacuum-degassed distilled water in the glove-box portion of the cluster tool. Results Figure 1b shows XPS spectra of both sides of the cleave point taken after separation in liquid nitrogen of the structure shown in Figure 1a. Small amounts of cadmium, tellurium, and sulfur were found on the tin oxide side, whereas no detectable tin was observed on the CdS-CdTe side. Auger electron microscopy of both sides (CdS side shown) indicated mostly featureless elemental composition images except for electron-beam induced desorption of chlorine and to a lesser extent oxygen on the edges of the images. The laterally uniform composition and the fact that the tin oxide substrate is easily detectable through a thin layer of Cd-S-Te-O combined with the average probe depth of these experiments means that the cleavage location occurs within about one nanometer of the tin oxide-CdS interface as indicated in Figure 1a. Visually, the exposed interfaces were mirror smooth. Atomic force microscopy data (Figure 1d) show that the surfaces typically have low roughness (Rq < 8 nm) over fairly large areas (400 µm2). Table 1. AES-derived atomic concentrations

Atomic Concentration (%) Sample O

S

Cl

Cd

Te

Sn

CdS side

21.2

15.1

19.1

35.9

8.8

---

SnO2 side

42.2

2.4

10.9

17.0

9.0

18.5

Elemental quantification of the AES and XPS data yield similar results and show a very large amount of chlorine (10-20%) at this interface (Table 1), one to two orders of magnitude higher than found through standard depth profiling techniques.15,16 A XPS sputter depth profile of the CdS side of a sample (Figure 2) shows that after sputtering ~30 nm into the emitter layer, reduced chlorine quantities of ~ 1-2% are found. The similarity of this value within the bulk of the material to what others have reported from depth profiling experiments provides confidence that the literature sensitivity factors for the various transitions used in the quantification procedure are reasonably accurate. It should be noted however

Figure 2. XPS sputter depth profile of CdS side of cleave.


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that the calculations used to arrive at the chlorine concentrations in Table 1 assume a composition that is uniform over the probe depth, and that the true surface composition of a layered structure will be different if depth-dependent composition is taken into account. One piece of information that is needed in the reduction of XPS data taken on layered structures is the identity of the various layers. A simple water solubility test was conducted on as-cleaved samples to assist in layer identification and to ascertain whether or not chlorine was present as over-layers or was distributed uniformly through the bulk of the interfacial region. After initial XPS measurements, cleaved samples were transferred in UHV back to the N2-filled glovebox where they were rinsed for 10 s in room temperature distilled water, blown dry, and then transferred back into the XPS system. Figure 3 shows the results after water washing. To compare line-shapes, the Cd 3d spectra and S 2s spectra have been normalized in maximum peak height. Chlorine and oxygen spectra are presented without such normalization to allow for intensity comparison.

Figure 3. XPS spectra showing effects of water washing on line-shapes (Cd and S) and on intensities (Cl 2p and O 1s). Cd and S spectra are normalized to maximum peak height.



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From the narrowing linewidth of the cadmium 3d spectra, it is clear that a cadmium-containing compound has been removed by water. From the chlorine 2p spectra, it is clear that chlorine was also removed by water exposure. Sulfur 2s spectra demonstrate that some oxidized sulfur (S6+, sulfate) from the CdS:O absorber was removed along with some oxygen.17 Given that the cadmium oxychloride Cd3Cl2O2 previously identified at CdTe surfaces after solution-based CdCl2 treatment is not water soluble,18 the straightforward interpretation of the current results is that an over-layer of a watersoluble compound of cadmium and chlorine, i.e. cadmium chloride, is responsible for the observed changes in XPS spectra that occur with water washing. Further confirmation of the identity of the cadmium species found at this interface was provided by cadmium Auger parameters (Figure S1). We note here that the position and shape of the weak Cd M4N45N45 Auger line depends strongly on the cadmium chemical state. The measured Auger parameter of 786.3 ± 0.1 eV from the chlorinecontaining CdS side of cleaved samples corresponds to pure CdS, implying that signals from the chlorinecontaining layer were dominated by the more abundant CdS.19 In contrast, the cadmium Auger parameter from the SnO2 side of the cleave location was 785.7 ± 0.2 eV, matching well with the Cd Auger parameter from our reference film of pure CdCl2 (785.8 ± 0.2 eV).

Figure 4. Angle-resolved XPS data from the SnO2 side (a) and the CdS side (b). Panel (c) shows the structure of CdCl2 for comparison. Panel (d) shows a schematic of the SnO2-CdS interface.


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A natural question that arises is how thick is the layer of CdCl2 at the tin oxide-cadmium sulfide interface? To answer this question, angle-resolved XPS experiments were performed on both the SnO2 and CdS sides of cleaved samples. Results are shown in Figure 4. Fitting of the angle-resolved data was constrained to take-off angles of less than 60 degrees to avoid elastic scattering effects.20 The positive slopes in the plots confirm that the cadmium chloride was present in a thin over-layer and not distributed uniformly over the probe depth of the experiment. Using the slopes of the lines and effective attenuation lengths (Figure S2), thickness of CdCl2 on both sides of the cleave location were calculated. A thickness corresponding to about one molecular layer of CdCl2 is found (4.2 ± 1 Å on the SnO2 side, 2.6± 1 Å on the CdS side). For reference, a view of the CdCl2 structure along [100] is provided. A schematic of the SnO2/CdS:O interface is shown in Figure 4d. The thin layer of material comprised of cadmium, sulfur, oxygen and tellurium that is found adjacent to the SnO2 transparent conducting oxide is denoted by CdSOTe. Discussion One might wonder why the thermo-mechanical cleavage of CdTe solar cells occurs where it does. Obviously a difference in thermal expansion coefficients is responsible for the applied stresses as a glassepoxy-cell sample is plunged into liquid nitrogen. Less obvious is why the mechanically weakest plane in a typical CdTe solar cell is defined by an atomically thin layer of cadmium chloride. It should be pointed out that delamination at the TCO-emitter interface is not just an academic issue associated with liquid nitrogen exposure, but in fact has long been a problem that is associated with over-treatment with CdCl2.21 A survey of the relatively sparse literature on cadmium chloride physical properties yields an appealing answer why a layer of CdCl2 would be associated with mechanical weakness: as might be apparent from Figure 4(c), CdCl2 is a true layered material that is directly analogous to the layered transition metal dichalcogenides and other low dimensional compounds.22 Within a (100) plane, strong ionic-covalent bonds form three-atom thick molecular sandwiches of chlorine-cadmium-chlorine. Between these Cl-Cd-Cl planes, relatively weak van der Waals forces bind the layers together. It is these weak van der Waals bonds that are presumably ruptured during the thermo-mechanical cleave process. Viewing CdCl2 as a layered material also provides an intuitive explanation for its passivation of the CdS/CdTe interfaces and possibly of the grain boundaries of the CdTe absorber itself. It should be noted that chlorine has been detected in high concentrations and in atomically thin layers (~3.4 Å) at grain boundaries in CdTe, although the exact chemical nature of this inter-grain chlorine is still unclear.23,24 The breaking of weak van der Waals bonds would not cause energetically deep dangling bond states that are efficient recombination centers, providing “chemical” passivation. Because bulk CdCl2 is a high bandgap material (5.8 eV), an atomically thin layer of CdCl2 could also, depending on the energy band alignment, provide field effect passivation while still allowing charge carrier transport via tunneling. Understanding that CdCl2 exists as two dimensional nanosheets within at least some parts of CdTe solar cells also provides guidance for improved post-growth processing. In a recent work looking for alternatives to use of CdCl2, the use of which has been described as both expensive and environmentally risky, workers found that post-growth treatment of CdTe films with MgCl2 provided about the same benefits as CdCl2 and that NaCl and KCl provided no benefits.25 Although the authors’ explanation for this effect was that sodium and potassium act as electrically detrimental impurities in CdTe, it also 7 ACS Paragon Plus Environment


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happens to be true that MgCl2 is a layered material like CdCl2.22 Sodium and potassium chloride are not. It is possible that other layered materials such as PbI2 could provide the same passivating effects as CdCl2 and MgCl2 yet also provide better interfacial transport properties because of smaller bandgaps and/or better energy band alignments. Another consideration raised by the presence of 2D metal halides in solar cells stems from their anisotropic electrical properties: in-plane electrical conductivities in 2D metal halides can be 103 times larger than in the direction normal to the molecular layers.22 Assuming that inter-grain chlorine found by previous workers in the absorber is in the same form as at the SnO2-CdS interface, we speculate that 2D CdCl2 nanosheets could be the electron corridors that have been recently detected at grain boundaries in CdTe solar cells.26 Finally, although CdTe-based photovoltaic panels are generally quite robust with regards to environmental exposure, the presence of a buried yet water-soluble layer in the standard device architecture could be the focus of further reliability studies. Conclusions We have utilized a thermo-mechanical lift-off technique to examine the tin oxide/cadmium sulfide interface in completed superstrate CdTe solar cells. We show that the lift-off happens within a nanometer of the SnO2/CdS interface, and that both sides of the cleave location are covered with a single CdCl2 molecular layer about four angstroms thick. This buried CdCl2 layer is water soluble, a fact that could bear further examination from a module reliability standpoint. We call attention to the fact that CdCl2, similar to transition metal dichalcogenides and graphite, is a layered material. Recognizing that 2D CdCl2 nanosheets commonly exist within CdTe solar cells provides new perspectives on seemingly disparate aspects of this PV technology. These include why thermo-mechanical cleavage works the way it does, why some metal halides work well in post-growth processing, and why some do not. Our results shine light on a little known class of two dimensional layered materials that include the perovskite precursors PbI2 and PbCl2, and call for new efforts, particularly theoretical efforts, to understand how the 2D nanoscale properties of these interesting materials differ from those of the bulk. Acknowledgments This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08GO28308 with the National Renewable Energy Laboratory. References (1) (2)

(3)

(4)

Green, M. A.; Emery, K.; Hishikawa, Y.; Warta, W.; Dunlop, E. D. Solar Cell Efficiency Tables (Version 48). Prog. Photovolt. Res. Appl. 2016, 24 (7), 905–913. Burst, J. M.; Duenow, J. N.; Albin, D. S.; Colegrove, E.; Reese, M. O.; Aguiar, J. A.; Jiang, C.-S.; Patel, M. K.; Al-Jassim, M. M.; Kuciauskas, D.; Swain, S.; Ablekim, T.; Lynn, K. G.; Metzger, W. K. CdTe Solar Cells with Open-Circuit Voltage Breaking the 1 V Barrier. Nat. Energy 2016, 1, 16015. Reese, M. O.; Perkins, C. L.; Burst, J. M.; Farrell, S.; Barnes, T. M.; Johnston, S. W.; Kuciauskas, D.; Gessert, T. A.; Metzger, W. K. Intrinsic Surface Passivation of CdTe. J. Appl. Phys. 2015, 118 (15), 155305. Major, J. D. Grain Boundaries in CdTe Thin Film Solar Cells: A Review. Semicond. Sci. Technol. 2016, 31 (9), 093001. 8 ACS Paragon Plus Environment

Page 13 of 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(5)

(6) (7) (8) (9) (10) (11) (12)

(13) (14) (15)

(16)

(17)

(18)

(19)

(20)

(21) (22)

Bonef, B.; Haas, B.; RouvièRe, J.-L.; André, R.; Bougerol, C.; Grenier, A.; Jouneau, P.-H.; Zuo, J.-M. Interfacial Chemistry in a ZnTe/CdSe Superlattice Studied by Atom Probe Tomography and Transmission Electron Microscopy Strain Measurements. J. Microsc. 2016, 262 (2), 178–182. Winiarski, B.; Gholinia, A.; Mingard, K.; Gee, M.; Thompson, G. E.; Withers, P. J. Broad Ion Beam Serial Section Tomography. Ultramicroscopy 2017, 172, 52–64. McCaffrey, J. P.; Phaneuf, M. W.; Madsen, L. D. Surface Damage Formation during Ion-Beam Thinning of Samples for Transmission Electron Microscopy. Ultramicroscopy 2001, 87 (3), 97–104. Surface Analysis by Auger and X-Ray Photoelectron Spectroscopy; Briggs, D., Grant, J. T., Eds.; IM Publ. [u.a.]: Chichester, 2003. Henrich, V. E.; Cox, P. A. The Surface Science of Metal Oxides, 1st paperback ed. (with corr.).; Cambridge Univ. Press: Cambridge, 1996. Yates, J. T. Experimental Innovations in Surface Science: A Guide to Practical Laboratory Methods and Instruments; Springer [u.a.]: New York, NY Berlin, 1998. Albin, D. S.; Yan, Y.; Al-Jassim, M. M. The Effect of Oxygen on Interface Microstructure Evolution in CdS/CdTe Solar Cells. Prog. Photovolt. Res. Appl. 2002, 10 (5), 309–322. Meysing, D. M.; Reese, M. O.; Warren, C. W.; Abbas, A.; Burst, J. M.; Mahabaduge, H. P.; Metzger, W. K.; Walls, J. M.; Lonergan, M. C.; Barnes, T. M.; Wolden, C. A. Evolution of Oxygenated Cadmium Sulfide (CdS:O) during High-Temperature CdTe Solar Cell Fabrication. Sol. Energy Mater. Sol. Cells 2016, 157, 276–285. Perkins, C. L. Molecular Anchors for Self-Assembled Monolayers on ZnO: A Direct Comparison of the Thiol and Phosphonic Acid Moieties. J. Phys. Chem. C 2009, 113 (42), 18276–18286. NIST Standard Reference Database 82. Abbas, A.; West, G. D.; Bowers, J. W.; Isherwood, P.; Kaminski, P. M.; Maniscalco, B.; Rowley, P.; Walls, J. M.; Barricklow, K.; Sampath, W. S.; Barth, K. L. The Effect of Cadmium Chloride Treatment on Close-Spaced Sublimated Cadmium Telluride Thin-Film Solar Cells. IEEE J. Photovolt. 2013, 3 (4), 1361–1366. Emziane, M.; Durose, K.; Romeo, N.; Bosio, A.; Halliday, D. P. A Combined SIMS and ICPMS Investigation of the Origin and Distribution of Potentially Electrically Active Impurities in CdTe/CdS Solar Cell Structures. Semicond. Sci. Technol. 2005, 20 (5), 434–442. Duncan, D. A.; Kephart, J. M.; Horsley, K.; Blum, M.; Mezher, M.; Weinhardt, L.; Häming, M.; Wilks, R. G.; Hofmann, T.; Yang, W.; Bär, M.; Sampath, W. S.; Heske, C. Characterization of Sulfur Bonding in CdS:O Buffer Layers for CdTe-Based Thin-Film Solar Cells. ACS Appl. Mater. Interfaces 2015, 7 (30), 16382–16386. Waters, D. M.; Niles, D.; Gessert, T. A.; Albin, D.; Rose, D. H.; Sheldon, P. Surface Analysis of Cdte After Various Pre-Contact Treatments. In Proceedings of the 2nd World Conference on Photovoltaic Energy Conversion; Vienna, Austria, 1998. Handbook of X-Ray Photoelectron Spectroscopy: A Reference Book of Standard Spectra for Identification and Interpretation of XPS Data, Update.; Moulder, J. F., Chastain, J., Eds.; PerkinElmer Corporation: Eden Prairie, Minn, 1992. Cumpson, P. J.; Seah, M. P. Elastic Scattering Corrections in AES and XPS. II. Estimating Attenuation Lengths and Conditions Required for Their Valid Use in Overlayer/Substrate Experiments. Surf. Interface Anal. 1997, 25 (6), 430–446. Wu, X. High-Efficiency Polycrystalline CdTe Thin-Film Solar Cells. Sol. Energy 2004, 77 (6), 803– 814. Preparation and Crystal Growth of Materials with Layered Structures; Lieth, R. M. A., Ed.; Physics and chemistry of materials with layered structures; D. Reidel Pub. Co: Dordrecht, Holland Boston, 1977.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(23)

(24)

(25) (26)

Page 14 of 14

Harvey, S. P.; Teeter, G.; Moutinho, H.; Al-Jassim, M. M. Direct Evidence of Enhanced Chlorine Segregation at Grain Boundaries in Polycrystalline CdTe Thin Films via Three-Dimensional TOFSIMS Imaging: Chlorine Segregation at Grain Boundaries in CdTe Thin Films. Prog. Photovolt. Res. Appl. 2015, 23 (7), 838–846. Poplawsky, J. D.; Li, C.; Paudel, N. R.; Guo, W.; Yan, Y.; Pennycook, S. J. Nanoscale Doping Profiles within CdTe Grain Boundaries and at the CdS/CdTe Interface Revealed by Atom Probe Tomography and STEM EBIC. Sol. Energy Mater. Sol. Cells 2016, 150, 95–101. Major, J. D.; Treharne, R. E.; Phillips, L. J.; Durose, K. A Low-Cost Non-Toxic Post-Growth Activation Step for CdTe Solar Cells. Nature 2014, 511 (7509), 334–337. Luria, J.; Kutes, Y.; Moore, A.; Zhang, L.; Stach, E. A.; Huey, B. D. Charge Transport in CdTe Solar Cells Revealed by Conductive Tomographic Atomic Force Microscopy. Nat. Energy 2016, 1, 16150.


Two-Dimensional Cadmium Chloride Nanosheets in Cadmium

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