Subscriber access provided by Queen's University Library
Article 3
1-x
x
4
Synthesis and Characterization of Cu(Sb As)S Semiconducting Nanocrystal Alloys with Tunable Properties for Optoelectronic Device Applications Robert B Balow, Caleb K. Miskin, Mahdi M. Abu-Omar, and Rakesh Agrawal Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b03850 • Publication Date (Web): 30 Nov 2016 Downloaded from http://pubs.acs.org on December 5, 2016
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Chemistry of Materials is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 8
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
Chemistry of Materials
Synthesis and Characterization of Cu3(Sb1-xAsx)S4 Semiconducting Nanocrystal Alloys with Tunable Properties for Optoelectronic Device Applications Robert B. Balow,†,1 Caleb K. Miskin,‡ Mahdi M. Abu-Omar†,‡,2 and Rakesh Agrawal‡,* †
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, United States
‡
School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, IN 47907, United States ABSTRACT: A synthetic method for producing monodisperse Cu3(Sb1-xAsx)S4 nanocrystals (NCs) with highly tunable semiconducting properties is discussed. Additionally, significant improvement in collectible photocurrent is observed for arsenic-rich compositions, with a 10-fold improvement in photocurrent density from Cu3AsS4 NC thin films compared to the more well-studied Cu3SbS4 composition. Interestingly, this improvement in photocurrent is observed despite the increased optical band gap of the arsenic-rich compositions. These results suggest Cu3AsS4 and arsenic-rich compositions of Cu3(Sb1-xAsx)S4 may yield higher photocurrent densities for solar conversion devices. Furthermore, the simple and robust synthesis, scalable spray coating strategy and highly tunable nature of the NCs provides a foundation encompassing numerous fields requiring inexpensive and earth abundant semiconducting materials.
INTRODUCTION
absorber layer was fabricated by magnetron sputtering having an efficiency of 0.46%, demonstrating the viability of this material class.24 A synthetic protocol to produce tightly controlled I3-V-VI4 NCs with tunable electronic and physical properties is therefore highly advantageous, as this will present new opportunities for a number of avenues utilizing low-cost and earth abundant semiconductor materials.
Solution processed nanocrystals (NCs) offer a remarkably scalable and tunable route to high-performance thin film materials suitable for thermoelectrics,1–4 sensors,5,6 photovoltaics,7–9 optoelectronics10 and catalysts.11,12 The small size of the NCs offers several advantages over larger bulk materials including size dependent electronic and physical properties and solution processability through formation of colloidal NC "inks".13 Rapid production of thin films can then be accomplished via spray coating or printing these NC inks, increasing production rates and lowering manufacturing costs.14–17
Herein we report a simple, solution-processable strategy to obtain impurity free Cu3(Sb1-xAsx)S4 (CSbAS) semiconducting NC alloys with compositionally tunable optical band gap energies. All synthesized CSbAS NC compositions had an average size of about 7-8 nm and crystallize in a tetragonal crystal structure. No observable impurity phases were detectable in the Raman spectra or X-ray diffraction patterns of the CSbAS NCs. Spray coated CSbAS NC thin films on molybdenum-coated glass produced significant photocurrent upon solar simulated (AM1.5G) illumination in a photoelectrochemical cell containing Na2S electrolyte. Increasing the elemental composition of arsenic resulted in increased optical band gap energy determined by UV Vis spectroscopy. Interestingly, the collected photocurrent density under solar-simulated illumination of the Cu3AsS4 thin films demonstrated a 10fold improvement compared to the more well-studied Cu3SbS4 thin films, despite the Cu3AsS4 thin films having a larger optical band gap energy. These findings suggest incorporating arsenic into the more well studied Cu3SbS4
In the last five years, NC derived thin film photovoltaics have demonstrated solar conversion efficiencies reaching as high as 15% for Cu(In,Ga)(S,Se)2 (CIGS).9 Unfortunately, low earth abundance of indium ultimately limits the scalability of this system.18 For this reason, more abundant solar absorption materials, such as Cu3AsS419 (CARS) and Cu3SbS420,21 (CANS) have gained considerable attention due to their commonalities with CIGS, such as direct band gap transition, high absorption coefficient and ideal band gap energy for use in photovoltaics. Importantly, significant photocurrent collection has been shown for both CARS and CANS NC thin films in electrochemical cells,19,22 also making these I3-V-VI4 materials useful candidates for other technologies utilizing solar absorption, such as sensitizers in quantum dot sensitized solar cells (QDSSCs).23 Recently, a solar cell utilizing Cu3SbS4 as the
1
ACS Paragon Plus Environment
Chemistry of Materials
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
class of materials may greatly improve the solar energy conversion performance of this exciting class of materials.
Page 2 of 8
The light yellow supernatant was discarded and the pelleted precipitate was re-suspended with ~5 mL of hexane and vortexed for 10 s. The centrifuge tube was then topped with ethanol and centrifuged as described previously. The supernatant was discarded and the resuspension and centrifugation steps were repeated one additional time. The supernatant was discarded and the particles were re-suspended in ~5 mL of toluene and stored for use later.
MATERIALS AND METHODS Materials. Copper (I) chloride (99.999%, CuCl) was obtained from Strem. Arsenic trichloride (99.99%, AsCl3), antimony trichloride (99.95%, SbCl3) and sulfur (99.99%, S) were obtained from Sigma-Aldrich. Oleylamine (≥8090%, OLA) was obtained from Acros Organics. Ethanol (200-proof) was obtained from Koptec and toluene (99.5%) was purchased from Macron Chemicals. Sodium sulfide nonahydrate (Na2S·9H2O, 98.0%) was obtained from Alfa Aesar. All reagents were used as received except for OLA, which was degassed by three freeze-pump-thaw cycles prior to being stored in an inert environment. Electrolyte solutions were prepared with ultrahigh purity water (Millipore Synergy UV Water Purification System) with a resistivity of 18.2 MΩ·cm at 25 °C.
Characterization. X-ray diffraction (XRD) data in grazing incidence mode were collected using a Rigaku SmartLab diffractometer with an incidence angle of 0.5° in parallel beam geometry with a Cu Kα X-ray source. Raman spectra were acquired using a Horiba/Jobin-Yvon LabRAM HR800 confocal microscope with a 633-nm He:Ne laser through a 100× objective lens. Scanning electron microscopy energy dispersive X-ray spectroscopy data (SEM-EDS) spectra were obtained using a FEI Quanta 3D FEG Dual-beam field emission scanning electron microscope with a 20 kV electron beam. Bulk SEM-EDS analysis was performed on drop-casted Cu3(Sb1-xAsx)S4 NCs suspended in toluene onto a silicon wafer and analyzed using AZtec software with a standardless quantitative analysis based on the Cliff-Lorimer method. Three random spots were analyzed for each composition to obtain averages and standard deviation. Optical band gap energies were extrapolated from Tauc plots generated by measuring the absorbance of diluted suspensions of the CSbAS NCs in toluene using a Perkin Elmer Lambda 950 spectrophotometer. All solutions were sonicated for 30 min prior to measuring to ensure colloidal stability. Quartz cuvettes with a 1 cm path length were used to hold the suspensions for the absorbance measurements. TEM was performed on a FEI Titan at 300 kV. Samples were prepared by drop casting a dilute suspension of particles in toluene on an ultrathin carbon film (
