Chemical Synthesis Of Cu(In_1-xAl_x)Se₂Compound Nanocrystals By Organic Amines-assisted Polyol Based Solution Process

In this dissertation, single-phase, well-dispersed and near-granular and flakeshape quaternary chalcopyrite Cu(In1-xAlx)Se2(CIASe) nanocrystals were synthesizedby a facile, air pressure hot-injection process using triethylenetetramine(TETA)-andethylenediamine(En)-assisted triethylene glycol(TEG) based solution.The research results showed that En and TETA played crucial roles in thesynthesis of CIASe nanocrystals and cations co-injection style is the best syntheticmethod. The En reagent had better assisting effects when it was used alone than thatwhen En and hydrazine hydrate were used together. Tetragonal chalcopyrite CIASenanocrystals could be synthesized in the range of1ml-4ml of En addition ut residualSe phase was observed at high En added amount which may be attributed to anenhanced complexing role of En with Se precursor species at high En added amount.The products showed a mixed growing morphology of nanoparticles and nanoplatesand more nanoplates would appear with increased addition of En.In TETA assisted TEG synthesis, the products showed the single CIASe phasewhen TETA added amount was2ml and3ml. The In/Al atomic ratio of the productswith high TETA addition, i.e.6%by vol and8%by vol, was well consistent with thetarget ratio of0.75/0.25in fed solution. All the products syhthesized with differentaddion of TETA assisted showed the near-granular nanocrystals and no obviouschange in morphology was obversed. With rising solution temperature, the diffractionpeaks of chalcopyrite CIASe phase clearly appeared and became strong but hexagonalSe phase with the decreasing diffraction peak intensity also existed in the temperaturerange of190°C-250°C. Single phase chalcopyrite CIASe was synthesized at270°C.With solution temperature increasing, the diameter size and formed proportion of theplate-shaped nanocrystals tended to ecrease, and near spherical nanoparticlesappeared more. At temperature270°C, the formed products were almost nearspherical nanoparticles and the particle size was around20nm. Addition of PVPimproved the dispersity of synthesized nanocrystals significantly and the meanparticle size tended to be more uniform with more PVP added. The reaction analysisshowed that nucleation of quaternary CIASe compound was rapid and the nucleidirectly grew into near-granular shaped CIASe nanoparticles within a short growthduration. Extending reaction time obviously unchanged the phase of the CIASenanocrystals but the Ostwald ripening could lead to slight size increase and narrow size distribution. The Al/In atomic ratios of the synthesized CIASe nanocrystals wereable to be tuned by varying In/Al atomic ratios in feeding solutions where x was in therange of0~0.5of Cu(In1-xAlx)Se2and band gap energy could be tuned in the range of1.06eV-1.78eV.This TETA-assisted TEG solution approach may provide a low-cost, facile andeco-friendly processing way to prepare quaternary chalcopyrite Cu(In1-xAlx)Se2nanocrystals for developing low-cost thin film solar cells by ink-deposited fabricationtechnique.