Aerosol Spray Pyrolysis Synthesis of CZTS Nanostructures for Photovoltaic Applications

Master of Science, Graduate Program in Mechanical Engineering
University of California, Riverside, August 2015
Dr. Lorenzo Mangolini, Chairperson

As harmful effects caused by the extraction, purification, and combustion of natural resources for energy generation become more clearly understood, the need for economically competitive renewable energy becomes more desirable. Solar energy-generation is a technologically feasible method, though its primary drawback is cost. Traditional single-crystal silicon-based photovoltaics are too expensive to compete with nonrenewable energy generation, while alternative materials such as cadmium telluride and copper-indium-gallium-selenide contain expensive and unsustainable elements, while cadmium is a known carcinogen. Copper-zinc-tin-sulfide (CZTS) is an another alternative material, though the technology is not yet advanced enough to have reached the market.

The  work  presented  is  a  study  of  the  viability  of  synthesizing  CZTS nanostructures using aerosol spray pyrolysis in an inexpensive, environmentally friendly,  and  industry-scalable  way.  We  aerosolize  a  precursor  solution  with dissolved  copper,  zinc,  and  tin  compounds  and  pass  the  droplets  through  a furnace,  where  the  precursors  dissolve and  thermally  form  CZTS  structures. Using this method, we can generate thin films—by placing a substrate within the  furnace—and  nanoparticles.  While  stoichiometric  CZTS  seems  to  be formed consistently, the films grown tend to be inhomogeneous in composition and  morphologically  unstable,  yielding  an  inefficient  material  for two-dimensional  photovoltaics.  Nanoparticle  synthesis  seems  to  be  the  more appropriate application of spray pyrolysis with this material system. We have shown the ability to control the composition and doping of CZTS nanoparticles, and preliminary efforts in coating and sintering the nanoparticles into crystalline films are promising.