Chemical Synthesis Of Quaternary Cu-in-ga-se Compound Nanocrystals By Organoalkali-assisted Polyol Based Solution Process

Cu(In,Ga)Se2(CIGSe) chalcopyrite compound is a leading light-absorbingmaterial in the development field of thin film solar cells due to its unique optical andelectric properties. In this dissertation, organoalkali-assisted polyol solution chemicalsynthesis was applied to prepare quaternary chalcopyrite CuIn1-xGaxSe2nanocrystals(0≤x≤1). Synthetic reaction systems, organoalkali species, reaction temperatures,refluxing time, amounts of PVP, Se/(Cu+In+Ga) and Cu/(In+Ga) atomic ratios wereinvestigated in order to optimize the processing parameters. The synthesized productswere characterized by XRD, TEM/HRTEM, FESEM, EDX, UV-vis-NIR, ICP-MS,Raman measurements to probe phase crystallization, growing morphology, chemicalcomposition and optical properties. Reaction mechanism was discussed according tothe exprimental results, simultaneously, the organoalkali-assisted effects wasqualitatively described based on the dynamic mechanism.The research results showed that triethylenetetramine, as an organoalkaliassisting agent, was able to promote supersaturation balance among each individualelement species and benefit the formation of target quaternary CIGSe compounds.Strong polarity of the solvent used and high synthetic temperature actually activatedelement Ga to participate the synthesis reaction. Based on the synthetic reactionprocess, a burst nucleation and early growth of quasi-ternary CuInSe2were completedwithin30seconds during hot-injection process and Ga species reacted gradually asextending reaction time to form the quaternary CIGSe compounds finally. It is alsoseen that simply changing Se/(Cu+In+Ga) and Cu/(In+Ga) atomic ratios in feedingreaction solutions could not achieve well-controlled stoichiometry of nanocrystalssynthesized. In addition, polyvinylpyrrolidone, as a dispersant, with small addingamount obviously enhanced the dispersing stability of nanocryatal products. In oneword, triethylenetetramine-assisted diethylene glycol solution synthesis was a facileand effective way to control chemical stoichiometry and band-gap energies forsingle-phase, well-dispersed, near-granular shaped CuIn1-xGaxSe2nanocrystals. Theaverage crystallite size of CuInSe2, CuIn0.7Ga0.3Se2, CuIn0.5Ga0.5Se2, CuIn0.6Ga0.4Se2and CuGaSe2nanocrystals synthesized were19.36nm,15.62nm,12.48nm,10.91nmand10.04nm, respectively, and the corresponding band-gap energies were1.05eV,1.22eV,1.34eV,1.42eV and1.70eV.