Article pubs.acs.org/cm
Cite This: Chem. Mater. 2017, 29, 9328-9339
Evolution of Morphology and Composition during Annealing and Selenization in Solution-Processed Cu2ZnSn(S,Se)4 James A. Clark,† Alexander R. Uhl,† Trevor R. Martin,‡ and Hugh W. Hillhouse*,† †
Department of Chemical Engineering, University of Washington, Seattle, Washington 98195-1750, United States Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195-2120, United States
‡
S Supporting Information *
ABSTRACT: Cu2ZnSn(S,Se)4 absorbers deposited from a nontoxic, DMSO-based molecular ink have yielded the most efficient, hydrazine-free Cu2ZnSn(S,Se)4 photovoltaic (PV) device made through solution-processing. Although this chemistry has been widely adopted, absorber morphologies with a device-limiting fine-grained bottom layer are often reported. Here we demonstrate how the annealing profile of coatings from this ink critically affect absorber morphologies. Calibrated glow discharge optical emission spectroscopy (GDOES) is used to determine depth-dependent elemental ratios and atomic concentrations of impurities before and after selenization. An annealing temperature of 400 °C is shown to exhibit the most pronounced fine-grained bottom layer, which contains 10 atom % carbon (C) and 5 atom % nitrogen (N). Raman analysis of the mechanically exfoliated, fine-grained layer reveals that it contains amorphous carbon nitride, which is attributed to the polymerization of thiourea decomposition products during annealing. An annealing temperature of 300 °C avoids this polymerization and allows C and N to escape during selenization, while an annealing temperature of 500 °C vaporizes C and N compounds before selenization. The annealing profile of 500 C 1.5 min/layer removes nearly all but ∼0.25 atom % of C and N, which impedes the formation of a fine-grained layer and allows for a PV device efficiency of 10.7%. It is also shown how lithium-doping enhances sodium transport from the soda-lime glass substrate. CZTS nanoparticle (NP) inks,5,6 both of which led to devices with PCEs near 1%. PCEs were quickly increased to 7.2% with CZTS NP inks;7 however, devices made from this process have not surpassed 9.3% to date.8 The methoxy-ethanol process has improved device PCE as well,9 with a recent result reporting a device PCE of 10.1%.10 Su et al. adopted the methoxy-ethanol chemistry to fabricate Cd-alloyed kesterite devices which lead to device PCEs up to 9.2%.11 Other notable solution processes which have led to high-PCE kesterite devices include the following: spray-coated colloidal water-and-ethanol-based inks (PCE 10.8%)12,13 and solutions of Cu, Zn, Ge, and Sn salts and thiourea in DMF (PCE 11.0%).14 In this work, we focus on a DMSO-based solution of Cu, Zn, and Sn salts and thiourea (hereafter referred to as DMSO molecular ink) to deposit CZTSSe absorber layers, first described by Ki and Hillhouse.15 Xin et al. later revealed the importance of redox reactions in this ink.16 In a subsequent report, Xin et al. showed that lithium-doping of the DMSO molecular ink significantly improves device PCE.17 Doping the ink with 2.5% LiCl/metals
1. INTRODUCTION Cu2ZnSn(S,Se)4-based (CZTSSe-based) thin-film solar cells are an exciting prospect for inexpensive photovoltaic (PV) electricity generation due to their high absorption coefficient, earth-abundant constituents, and tunable bandgap of 1.0−1.5 eV, which is optimal for the solar spectrum.1 Of the deposition techniques available for CZTSSe, solution-processed absorbers are particularly interesting because of the possibility of low capital expenditure (CAPEX) required to build a manufacturing facility, which is one of the most significant barriers to growth of the PV industry.2 Hydrazine-based solution processes have led to CZTSSe devices with a power conversion efficiency (PCE) of 12.6%, which is the most efficient device using this absorber material produced from any deposition technique.3 One of the key reasons for the success of this process is that hydrazine is able to directly solvate metal chalcogenides but then decompose and leave cleanly upon annealing without leaving behind impurities in the film. However, hydrazine is explosive and highly toxic, which limits its practical potential as a low-CAPEX option to scale CZTSSe module production. A number of other CZTSSe solution processes utilizing less hazardous constituents have been explored. The first reports of solution-processed CZTSSe absorbers used either solutions of Cu, Zn, and Sn salts and thiourea in methoxy-ethanol4 or © 2017 American Chemical Society
Received: August 4, 2017 Revised: September 26, 2017 Published: September 27, 2017 9328
DOI: 10.1021/acs.chemmater.7b03313 Chem. Mater. 2017, 29, 9328−9339
Article
Chemistry of Materials
coating. The elemental ratios based on the as-added constituents were as follows: Cu/(Zn + Sn) = 0.76; Zn/Sn = 1.17; and S/(Cu + Zn + Sn) = 1.35. This ink was used for all presented data, with the exception of the LiCl-doped precursor films in Figure 9. Details for the Li-doped ink can be found in the SI. 2.2. Precursor Film Deposition. Molybdenum-coated soda-lime glass (MSLG) was first cleaned by sequential sonication in water, acetone, and 2-propanol, each for 10 min. The molecular ink was then spin-coated onto clean MSLG substrates at a spin speed of 2000 rpm for 60 s and then immediately annealed on a precision hot plate with cover and temperature regulator (Harry Gestigkeit Gmbh PZ 28− 3TD). The hot-plate cover was closed during annealing. Annealing time and hot-plate set point were varied between 1 and 3 min/layer and 300 to 500 °C, respectively. This process was repeated seven times to build up a precursor film thickness of ∼1.2 μm. All molecular ink preparation and spin-coating was performed inside of a N2-filled glovebox with O2 and H2O below 10 ppm. 2.3. Selenization and Device Fabrication. Precursor films were annealed with elemental selenium in a vented graphite box inside a tube furnace. The selenizations were performed at a temperature of 540 °C for 20 min with a constant argon purge of 100 sccm. The tube furnace was then naturally cooled to room temperature over the course of approximately 2 h. After selenization, one film was taken for characterization, and the second was taken for device fabrication. Device fabrication was performed according to previous reports.15 Briefly, selenized films were immediately submerged in DI water for 5 min after selenization and then transferred into a heated CdSO4/ NH4OH/thiourea solution for chemical bath deposition of 40 nm CdS. By RF sputtering, 50 nm of i-ZnO and 250 nm of ITO were then deposited, and top contacts were deposited by thermal evaporation of nickel and aluminum through a shadow mask. Each device has an active area averaging 0.105 cm2; however, the exact area of every cell was individually measured and used to determine its current density value. After scribing, a 110 nm MgF2 antireflective coating was thermally evaporated onto the devices. 2.4. Thermogravimetric Analysis. Thermogravimetric analysis was performed on 31.5 mg of the DMSO-based molecular ink using a PerkinElmer TGA 7 instrument. The ink was transferred into an alumina crucible with a vented lid and heated from room temperature to 600 °C at a ramp rate of 1 °C/min under a constant nitrogen purge of 90 mL/min. 2.5. Film and Device Characterization. X-ray diffraction (XRD) was performed on both the precursor and selenized films with a Bruker F8 Discover. A Cu Kα X-ray source with an incident wavelength of 1.540 59 Å was used. Raman analysis was performed with a Renishaw inVia system equipped with the Leica DMIRBE inverted optical microscope using 514.5 and 785 nm excitation sources. Scanning electron microscopy (SEM) micrographs were collected with an FEI Sirion XL30 microscope using a 20 kV accelerating voltage. Current− voltage (J−V) measurements were performed using a Keithley 2400 source-measure unit in the dark and under 100 mW/cm2 simulated sunlight from a Newport AAA Oriel Sol3A solar simulator. The incident power was calibrated with a Newport Si reference cell. 2.6. Exfoliated CZTSSe Lift-Off Procedure. The mechanical exfoliation of CZTSSe films from the molybdenum back contact was performed according to a procedure described by Tai et al.31 A schematic of this procedure is presented in Figure S7a. The lift-off was accomplished by applying epoxy (Hardman Double/Bubble waterclear transparent epoxy) to the surface of a CZTSSe film and fixing a glass slide onto the surface with a clamp. After overnight curing, the glass slide was mechanically pried off, which separated the CZTSSe from the molybdenum, exposing the fine-grained layer. 2.7. Stoichiometry Measurements and Calibration of Glow Discharge Optical Emission Spectroscopy. Energy-dispersive Xray spectroscopy (EDX) data were collected with an Oxford EDX detector using an accelerating voltage of 20 kV. ICP-MS data were collected with a PerkinElmer ELAN-DRCe instrument with a frontend PerkinElmer 200 HPLC system. Further details for ICP-MS are described previously.32 Glow discharge optical emission spectroscopy (GDOES) data were collected using a Horiba GD-Profiler 2
leads to a device PCE of 11.8%, which is currently the highest PCE of a hydrazine-free, solution-processed CZTSSe device. All of the above solution routes are generally much safer than hydrazine; however, many of these processes can lead to multilayer absorber morphologies after selenization.7,8,10,13,16,18 Absorbers generally exhibit a large-grained upper layer and a fine-grained under-layer, which is rich in impurities. Depending on the ink chemistry, this fine-grained layer can have a number of different impurities and physical properties. The most wellstudied impurity-rich layer (IRL) of the above solution processes is the fine-grained layer produced from the CZTS nanoparticle process.8,19,20 Martin et al. showed that this IRL is composed of graphitic carbon produced from the pyrolysis of the coordinating ligands during annealing and that the degree of crystallization of the IRL can significantly affect CZTSSe grain growth.19 Hages et al. examined the effect of various selenization conditions on grain growth and bilayer formation in CZTS nanoparticles.8 Wu et al. showed that the bilayer morphology could be avoided for the methoxy-ethanol-based ink process by performing a sulfurization prior to selenization.10 CZTSSe absorbers fabricated from the DMSO molecular ink process are often reported with a variety of multilayer morphologies.21−30 Moreover, devices in most of these studies suffer from low device PCEs (275 °C in multiple studies,21,22,24,29 which risks the oxidation of the metals to some extent and otherwise affects decomposition pathways. In this study, we performed TGA of the molecular ink under constant N2 flow from 25 to 600 °C to track the stages of degradation in an inert environment as shown in Figure 1. A summary of the
Table 2. Mass and Molar Balance of the Constituents of DMSO Molecular Ink
Figure 1. TGA of the DMSO molecular ink heated in N2 atmosphere with a ramp rate of 1 °C/min. Plot shading indicates ink constituents: blue, evolved solvents; red, evolved impurities; yellow, evolved species due to CZTS decomposition; and green, retained metal sulfides. Inset: spin-coated precursor films on glass annealed at different temperatures showing the onset of color change indicating metal sulfide formation.
be attributed to Sx and SnS vaporization, this suggests that some impurity elements remained in the film even at these highest temperatures. The TGA ramp of 1 °C/min up to 600 °C leads to a much higher thermal exposure than the brief anneals between spincoated layers. During TGA, the material spends 300 min above 300 °C, 200 min at about 400 °C, and 100 min above 500 °C. By contrast, films are only annealed at a maximum of 3 min/ layer (i.e. 21 min total exposure) during spin-coating in this study. Thus, the TGA data are a useful upper limit for impurity removal in a spin-coated thin film, since the impurities have a larger potential time window to volatilize. In the following sections, a number of annealing profiles with varying time and temperature between spin-coating layers were explored to
precursors’ constituents is presented in Table 1 and mass balance of these constiuents is presented in Table 2. From 25 to 150 °C, 66% of the mass had been lost which corresponds to the mass percent of DMSO and H2O in the ink as shown in the blue shaded region of Table 2, and 150 °C is also below the onset of the formation of light-absorbing metal sulfide species as shown in the inset of Figure 1. This suggests that the DMSO 9330
DOI: 10.1021/acs.chemmater.7b03313 Chem. Mater. 2017, 29, 9328−9339
Article
Chemistry of Materials
Figure 3a,b. For annealing temperatures at or below 400 °C, little to no crystallization of the metal sulfide precursor film is visible. However, at 500 °C, the film is readily crystallized, and crystallization increases with increasing annealing time. It is noted that because of the overlapping diffraction patterns, the crystalline phases of Cu2ZnSnS4, ZnS, and monoclinic CuSnS2 cannot be distinguished by XRD. Despite the differences in phase distribution and crystallinity, SEM results of all precursor films annealed at different conditions look identical, except for the 500 °C for 3 min/ layer condition. For all except this condition, precursor films have a porous, flat morphology with features 10% (shown in the SI). Films annealed at 400 °C, with a C- and Nenriched fine-grained layer, consistently led to devices with a low fill factor and PCE. Films annealed at 500 °C showed a range of morphologies, but all annealing times were shown to
Notes
James A. Clark: 0000-0003-4907-2649 Author Contributions
This manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS J.A.C., T.R.M., and H.W.H. acknowledge support from the National Science Foundation (NSF) Sustainable Energy Pathway (SEP) Award CHE-1230615. T.R.M. acknowledges support from NSF Division of Materials Research (DMR) Award 1533372. A.R.U. acknowledges the financial support from the Swiss National Science Foundation (SNSF) under the project P300P2_164660. The NanoTech (NTUF) user facility is acknowledged for GDOES, powder XRD, Raman, and SEM measurements. The Washington Nanofabrication Facility (WNF) is acknoledged for RF sputtering of TCOs. The authors thank Anna Murry, Liam Bradshaw, Micah Glaz, and David Baker for help with sample generation, GDOES measurements, Raman measurements, TCO deposition, respectively.
■
REFERENCES
(1) Nelson, J. The Physics of Solar Cells; Imperial College Press: London, UK, 2003. 9337
DOI: 10.1021/acs.chemmater.7b03313 Chem. Mater. 2017, 29, 9328−9339
Article
Chemistry of Materials (2) Powell, D. M.; Fu, R.; Horowitz, K.; Basore, P. A.; Woodhouse, M.; Buonassisi, T. The Capital Intensity of Photovoltaics Manufacturing: Barrier to Scale and Opportunity for Innovation. Energy Environ. Sci. 2015, 8, 3395−3408. (3) Wang, W.; Winkler, M. T.; Gunawan, O.; Gokmen, T.; Todorov, T. K.; Zhu, Y.; Mitzi, D. B. Device Characteristics of CZTSSe ThinFilm Solar Cells with 12.6% Efficiency. Adv. Energy Mater. 2014, 4, 1301465. (4) Tanaka, K.; Oonuki, M.; Moritake, N.; Uchiki, H. Cu(2)ZnSnS(4) Thin Film Solar Cells Prepared by Non-Vacuum Processing. Sol. Energy Mater. Sol. Cells 2009, 93, 583−587. (5) Guo, Q.; Hillhouse, H. W.; Agrawal, R. Synthesis of Cu2ZnSnS4 Nanocrystal Ink and Its Use for Solar Cells. J. Am. Chem. Soc. 2009, 131, 11672−11673. (6) Steinhagen, C.; Panthani, M. G.; Akhavan, V.; Goodfellow, B.; Koo, B.; Korgel, B. A. Synthesis of Cu2ZnSnS4 Nanocrystals for Use in Low-Cost Photovoltaics. J. Am. Chem. Soc. 2009, 131, 12554−12555. (7) Guo, Q.; Ford, G. M.; Yang, W. C.; Walker, B. C.; Stach, E. A.; Hillhouse, H. W.; Agrawal, R. Fabrication of 7.2% Efficient CZTSSe Solar Cells Using CZTS Nanocrystals. J. Am. Chem. Soc. 2010, 132, 17384−17386. (8) Hages, C. J.; Koeper, M. J.; Miskin, C. K.; Brew, K. W.; Agrawal, R. Controlled Grain Growth for High Performance NanoparticleBased Kesterite Solar Cells. Chem. Mater. 2016, 28, 7703−7714. (9) Su, Z. H.; Sun, K. W.; Han, Z. L.; Cui, H. T.; Liu, F. Y.; Lai, Y. Q.; Li, J.; Hao, X. J.; Liu, Y. X.; Green, M. A. Fabrication of Cu2ZnSnS4 Solar Cells with 5.1% Efficiency Via Thermal Decomposition and Reaction using a Non-Toxic Sol-Gel Route. J. Mater. Chem. A 2014, 2, 500−509. (10) Wu, S. H.; Chang, C. W.; Chen, H. J.; Shih, C. F.; Wang, Y. Y.; Li, C. C.; Chan, S. W. High-Efficiency Cu2ZnSn(S,Se)4 Solar Cells Fabricated through a Low-Cost Solution Process and a Two-Step Heat Treatment. Prog. Photovoltaics 2017, 25, 58−66. (11) Su, Z.; Tan, J. M. R.; Li, X.; Zeng, X.; Batabyal, S. K.; Wong, L. H. Cation Substitution of Solution-Processed Cu2ZnSnS4 Thin Film Solar Cell with over 9% Efficiency. Adv. Energy Mater. 2015, 5, 1500682. (12) Larramona, G.; Levcenko, S.; Bourdais, S.; Jacob, A.; Choné, C.; Delatouche, B.; Moisan, C.; Just, J.; Unold, T.; Dennler, G. FineTuning the Sn Content in CZTSSe Thin Films to Achieve 10.8% Solar Cell Efficiency from Spray-Deposited Water−Ethanol-Based Colloidal Inks. Adv. Energy Mater. 2015, 5, 1501404. (13) Larramona, G.; Bourdais, S.; Jacob, A.; Choné, C.; Muto, T.; Cuccaro, Y.; Delatouche, B.; Moisan, C.; Péré, D.; Dennler, G. 8.6% Efficient CZTSSe Solar Cells Sprayed from Water−Ethanol CZTS Colloidal Solutions. J. Phys. Chem. Lett. 2014, 5, 3763−3767. (14) Collord, A. D.; Hillhouse, H. W. Germanium Alloyed Kesterite Solar Cells with Low Voltage Deficits. Chem. Mater. 2016, 28, 2067− 2073. (15) Ki, W.; Hillhouse, H. W. Earth-Abundant Element Photovoltaics Directly from Soluble Precursors with High Yield using a Non-Toxic Solvent. Adv. Energy Mater. 2011, 1, 732−735. (16) Xin, H.; Katahara, J. K.; Braly, I. L.; Hillhouse, H. W. 8% Efficient Cu2ZnSn(S,Se)(4) Solar Cells from Redox Equilibrated Simple Precursors in DMSO. Adv. Energy Mater. 2014, 4, 1301823. (17) Xin, H.; Vorpahl, S. M.; Collord, A. D.; Braly, I. L.; Uhl, A. R.; Krueger, B. W.; Ginger, D. S.; Hillhouse, H. W. Lithium-Doping Inverts the Nanoscale Electric Field at the Grain Boundaries in Cu2ZnSn(S,Se)(4) and Increases Photovoltaic Efficiency. Phys. Chem. Chem. Phys. 2015, 17, 23859−23866. (18) Wang, W.; Shen, H.; Wong, L. H.; Yao, H.; Su, Z.; Li, Y. Preparation of High Efficiency Cu2ZnSn(S,Se)4 Solar Cells from Novel Non-Toxic Hybrid Ink. J. Power Sources 2016, 335, 84−90. (19) Martin, T. R.; Katahara, J. K.; Bucherl, C. N.; Krueger, B. W.; Hillhouse, H. W.; Luscombe, C. K. Nanoparticle Ligands and Pyrolized Graphitic Carbon in CZTSSe Photovoltaic Devices. Chem. Mater. 2016, 28, 135−145.
(20) Bucherl, C. N.; Oleson, K. R.; Hillhouse, H. W. Thin Film Solar Cells from Sintered Nanocrystals. Curr. Opin. Chem. Eng. 2013, 2, 168−177. (21) Haass, S. G.; Diethelm, M.; Werner, M.; Bissig, B.; Romanyuk, Y. E.; Tiwari, A. N. 11.2% Efficient Solution Processed Kesterite Solar Cell with a Low Voltage Deficit. Adv. Energy Mater. 2015, 5, 1500712. (22) Werner, M.; Keller, D.; Haass, S. G.; Gretener, C.; Bissig, B.; Fuchs, P.; La Mattina, F.; Erni, R.; Romanyuk, Y. E.; Tiwari, A. N. Enhanced Carrier Collection from CdS Passivated Grains in SolutionProcessed Cu2ZnSn(S,Se)4 Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 12141−12146. (23) Sutter-Fella, C. M.; Stückelberger, J. A.; Hagendorfer, H.; La Mattina, F.; Kranz, L.; Nishiwaki, S.; Uhl, A. R.; Romanyuk, Y. E.; Tiwari, A. N. Sodium Assisted Sintering of Chalcogenides and Its Application to Solution Processed Cu2ZnSn(S,Se)4 Thin Film Solar Cells. Chem. Mater. 2014, 26, 1420−1425. (24) Werner, M.; Sutter-Fella, C. M.; Romanyuk, Y. E.; Tiwari, A. N. 8.3% Efficient Cu2ZnSn(S,Se)4 Solar Cells Processed from SodiumContaining Solution Precursors in a Closed Reactor. Thin Solid Films 2015, 582, 308−312. (25) Schnabel, T.; Abzieher, T.; Friedlmeier, T. M.; Ahlswede, E. Solution-Based Preparation of Cu2ZnSn(S,Se)4 for Solar Cells Comparison of SnSe2 and Elemental Se as Chalcogen Source. IEEE J. Photovolt. 2015, 5, 670−675. (26) Neuwirth, M.; Zhou, H.; Schnabel, T.; Ahlswede, E.; Kalt, H.; Hetterich, M. A Multiple-Selenization Process for Enhanced Reproducibility of Cu2ZnSn(S,Se)4 Solar Cells. Appl. Phys. Lett. 2016, 109, 233903. (27) Abzieher, T.; Schnabel, T.; Hetterich, M.; Powalla, M.; Ahlswede, E. Source and Effects of Sodium in Solution-Processed Kesterite Solar Cells. Phys. Status Solidi A 2016, 213, 1039−1049. (28) Xiao, Z.-Y.; Yao, B.; Li, Y.-F.; Ding, Z.-H.; Gao, Z.-M.; Zhao, H.F.; Zhang, L.-G.; Zhang, Z.-Z.; Sui, Y.-R.; Wang, G. Influencing Mechanism of the Selenization Temperature and Time on the Power Conversion Efficiency of Cu2ZnSn(S,Se)4-Based Solar Cells. ACS Appl. Mater. Interfaces 2016, 8, 17334−17342. (29) Altamura, G.; Wang, M.; Choy, K.-L. Improving Efficiency of Electrostatic Spray-Assisted Vapor Deposited Cu2ZnSn(S,Se)4 Solar Cells by Modification of Mo/Absorber Interface. Thin Solid Films 2015, 597, 19−24. (30) Schnabel, T.; Ahlswede, E. On the Interface Between Kesterite Absorber and Mo Back Contact and Its Impact on Solution-Processed Thin-Film Solar Cells. Sol. Energy Mater. Sol. Cells 2017, 159, 290− 295. (31) Tai, K. F.; Gunawan, O.; Kuwahara, M.; Chen, S.; Mhaisalkar, S. G.; Huan, C. H. A.; Mitzi, D. B. Fill Factor Losses in Cu2ZnSn(SxSe1− x)4 Solar Cells: Insights from Physical and Electrical Characterization of Devices and Exfoliated Films. Adv. Energy Mater. 2016, 6, 1501609. (32) Uhl, A.; Katahara, J.; Hillhouse, H. Molecular-ink Route to 13.0% Efficient Low-Bandgap CuIn(S,Se)2 and 14.7% Efficient Cu(In, Ga)(S, Se)2 Solar Cells. Energy Environ. Sci. 2016, 9, 130−134. (33) Nelis, T.; Payling, R. Glow Discharge Optical Emission Spectroscopy: a Practical Guide; Royal Society of Chemistry: Cambridge, UK, 2003. (34) Madarász, J.; Bombicz, P.; Okuya, M.; Kaneko, S. Thermal Decomposition of Thiourea Complexes of Cu(I), Zn(II), and Sn(II) Chlorides as Precursors for the Spray Pyrolysis Deposition of Sulfide Thin Films. Solid State Ionics 2001, 141, 439−446. (35) Scragg, J. J.; Ericson, T.; Kubart, T.; Edoff, M.; PlatzerBjorkman, C. Chemical Insights into the Instability of Cu2ZnSnS4 Films during Annealing. Chem. Mater. 2011, 23, 4625−4633. (36) Fernandes, P. A.; Salome, P. M. P.; da Cunha, A. F. Study of Polycrystalline Cu2ZnSnS4 Films by Raman Scattering. J. Alloys Compd. 2011, 509, 7600−7606. (37) Fernandes, P. A.; Salome, P. M. P.; da Cunha, A. F. Growth and Raman Scattering Characterization of Cu(2)ZnSnS(4) Thin Films. Thin Solid Films 2009, 517, 2519−2523. 9338
DOI: 10.1021/acs.chemmater.7b03313 Chem. Mater. 2017, 29, 9328−9339
Article
Chemistry of Materials (38) Fontane, X.; Izquierdo-Roca, V.; Fairbrother, A.; EspindolaRodriguez, M.; Lopez-Marino, S.; Placidi, M.; Jawhari, T.; Saucedo, E.; Perez-Rodriguez, A. Selective Detection of Secondary Phases in Cu2ZnSn(S,Se)4 Based Absorbers by Pre-Resonant Raman Spectroscopy. IEEE Photovoltaic Spec. Conf., 34th 2013, 2581−2584. (39) Scragg, J. J. S.; Choubrac, L.; Lafond, A.; Ericson, T.; PlatzerBjorkman, C. A Low-Temperature Order-Disorder Transition in Cu2ZnSnS4 Thin Films. Appl. Phys. Lett. 2014, 104, 041911. (40) Cheng, A. J.; Manno, M.; Khare, A.; Leighton, C.; Campbell, S. A.; Aydil, E. S. Imaging and Phase Identification of Cu2ZnSnS4 Thin Films using Confocal Raman Spectroscopy. J. Vac. Sci. Technol., A 2011, 29, 051203. (41) Scragg, J. J.; Wätjen, J. T.; Edoff, M.; Ericson, T.; Kubart, T.; Platzer-Björkman, C. A Detrimental Reaction at the Molybdenum Back Contact in Cu2ZnSn(S,Se)4. Thin-Film Solar Cells. J. Am. Chem. Soc. 2012, 134, 19330−19333. (42) Wang, K. J.; Shin, B.; Reuter, K. B.; Todorov, T.; Mitzi, D. B.; Guha, S. Structural and Elemental Characterization of High Efficiency Cu(2)ZnSnS(4) Solar Cells. Appl. Phys. Lett. 2011, 98, 051912. (43) Romero, M. J.; Du, H.; Teeter, G.; Yan, Y. F.; Al-Jassim, M. M. Comparative Study of the Luminescence and Intrinsic Point Defects in the Kesterite Cu(2)ZnSnS(4) and Chalcopyrite Cu(In,Ga)Se(2) Thin Films used in Photovoltaic Applications. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 84, 165324. (44) Gershon, T.; Shin, B.; Bojarczuk, N.; Hopstaken, M.; Mitzi, D. B.; Guha, S. The Role of Sodium as a Surfactant and Suppressor of Non-Radiative Recombination at Internal Surfaces in Cu2ZnSnS4. Adv. Energy Mater. 2015, 5, 1400849. (45) Zhang, L. H.; Gong, H.; Wang, J. P. Thermal Decomposition Kinetics of Amorphous Carbon Nitride and Carbon Films. J. Phys.: Condens. Matter 2002, 14, 1697. (46) Chowdhury, A.; Cameron, D.; Hashmi, M. Vibrational Properties of Carbon Nitride Films by Raman Spectroscopy. Thin Solid Films 1998, 332, 62−68. (47) Ferrari, A.; Rodil, S.; Robertson, J. Interpretation of Infrared and Raman Spectra of Amorphous Carbon Nitrides. Phys. Rev. B: Condens. Matter Mater. Phys. 2003, 67, 155306. (48) Rodil, S.; Muhl, S.; Maca, S.; Ferrari, A. Optical Gap in Carbon Nitride Films. Thin Solid Films 2003, 433, 119−125. (49) Han, H.-X.; Feldman, B. J. Structural and Optical Properties of Amorphous Carbon Nitride. Solid State Commun. 1988, 65, 921−923. (50) Wang, S.; Gao, Q.; Wang, J. Thermodynamic Analysis of Decomposition of Thiourea and Thiourea Oxides. J. Phys. Chem. B 2005, 109, 17281−17289. (51) Ang, T. P.; Chan, Y. M. Comparison of the Melon Nanocomposites in Structural Properties and Photocatalytic Activities. J. Phys. Chem. C 2011, 115, 15965−15972. (52) Giovannozzi, A. M.; Rolle, F.; Sega, M.; Abete, M. C.; Marchis, D.; Rossi, A. M. Rapid and Sensitive Detection of Melamine in Milk with Gold Nanoparticles by Surface Enhanced Raman Scattering. Food Chem. 2014, 159, 250−256. (53) McMillan, P. F.; Lees, V.; Quirico, E.; Montagnac, G.; Sella, A.; Reynard, B.; Simon, P.; Bailey, E.; Deifallah, M.; Corà, F. Graphitic Carbon Nitride C6N9H3·HCl: Characterisation by UV and Near-IR FT Raman Spectroscopy. J. Solid State Chem. 2009, 182, 2670−2677. (54) Jiang, C.; Hsieh, Y.-T.; Zhao, H.; Zhou, H.; Yang, Y. Controlling Solid−Gas Reactions at Nanoscale for Enhanced Thin Film Morphologies and Device Performances in Solution-Processed Cu2ZnSn(S,Se)4 Solar Cells. J. Am. Chem. Soc. 2015, 137, 11069− 11075. (55) Yang, Y.; Huang, L.; Pan, D. A New Insight of Li-Doped Cu2ZnSn(S,Se)4 Thin Films: Li-Induced Na Diffusion from Soda Lime Glass by a Cation-Exchange Reaction. ACS Appl. Mater. Interfaces 2017, 9, 23878−23883.
9339
DOI: 10.1021/acs.chemmater.7b03313 Chem. Mater. 2017, 29, 9328−9339
