Structural and Optical Study of Ga 3+ Substitution in CuInS 2 Nanoparticles Synthesized by a One-Pot Facile Method Yaser Vahidshad, † Muhammad Nawaz Tahir, ‡ Azam Iraji Zad, § Seyed Mohammad Mirkazemi,* ,† Reza Ghasemzadeh, † Hannah Huesmann, ‡ and Wolfgang Tremel ‡ † School of Metallurgy and Material Engineering, Iran University of Science and Technology, Tehran 16844, Iran ‡ Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, D-55099, Mainz, Germany § Department of Physics, Sharif University of Technology, Tehran 11365-9161, Iran ABSTRACT: A one-pot method was used to synthesize CuIn x Ga 1-x S 2 nanoparticles by substituting In 3+ with Ga 3+ . The samples with composition of gallium ranging from 0% to 100% were synthesized by solving copper chloride, indium trichloride, gallium acetylacetonate, and thiourea as precursors in 1-octadecene, oleylamine, and oleic acid as noncoordinating, coordinating, and capping agent solvents, respectively. De- pending on the chemical composition and synthesis con- ditions, the morphology of the as-synthesized nanoparticles obtained was trigonal, semitrigonal, hexagonal, and quasi- spherical. X-ray photoelectron spectroscopy and X-ray dif- fraction confirmed that Ga 3+ substituted In 3+ without any segregation over a wide range. The as-synthesized CuIn x Ga 1-x S 2 nanoparticles showed narrow size distribution across the entire composition range (x =0-1) and band gap tuned in the range from 1.44 to 2.28 eV. The morphology, structure, and optical properties of the synthesized nanoparticles were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), UV- visible (UV-vis) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The mechanism of complex formation up to nanoparticle synthesis was also discussed. 1. INTRODUCTION Increasing demands on clean energy result in development of photovoltaic products. Thin film solar cells are interesting because they are lightweight, have good photostability, are cost- effective, and are able to be fabricated on flexible substrates. 1-6 Thin films based on CuIn x Ga 1-x (S 1-y Se y ) 2 (x, y =0-1) (CIGSSe) compounds are attractive due to the high solar absorption coefficient (more than 10 5 cm -1 ). Also, band gap tuning of the CIGSSe compounds can be adjusted from 0.98 eV for CISe to 2.40 eV for CGS which is a wide spectral region from visible to near-infrared. 7-10 Recent studies indicate that CIGSSe solar cells have exhibited the highest solar energy conversion efficiency (20.8%) among thin film solar cell groups. 11-15 They are fabricated by rather expensive methods such as molecular beam epitaxy, 16 coevaporation, 17 sputtering, 18 pulse laser de- position, 19 and electrodeposition. 20 One of the trends in this field is reducing the production cost by introducing low cost pre- paration protocols like printing methods. Quaternary chalcog- enide thin films can be prepared using colloidal nanocrystals that are synthesized by simple solution-based methods 21-25 such as chemical bath deposition, microwave-assisted synthesis, spray pyrolysis, solvothermal, hot injection, thermolysis, and other chemical wet methods for printing applications. 26-32 Controlling the stoichiometry and phase structure of quaternary CuIn x Ga 1-x S 2 is more difficult than ternary or binary compounds. Therefore, choosing a proper method for nanocolloid synthesis is really important to achieve an optimized morphology and structural and optical properties. 33-38 The one-pot thermolysis method as a promising method is based on controlling the nuclea- tion and growth of organometallic compounds (complex) by using proper solvents and capping agents. Various print- ing techniques are used, including dip coating, 39 ink jet printing, 40 drop casting, 41 roll-to-roll 42 spin, and spray coating methods. 43,44 In this contribution, we report on the solution synthesis of quaternary phase copper indium gallium sulfide colloidal Received: July 2, 2014 Revised: September 20, 2014 Article pubs.acs.org/JPCC © XXXX American Chemical Society A dx.doi.org/10.1021/jp506584a | J. Phys. Chem. C XXXX, XXX, XXX-XXX