Synthesis and Characterization of Ternary Metal Chalcogenides for Photovoltaic Applications

Abstract

With the aim to equalize solar energy and the energy production cost of fossil fuels, researchers had turned their efforts towards the development of new generations of solar cells. The synthe-sis of new materials with remarkable characteristics has been a major goal for the research community in order to overcome the limitations that had prevented the solar energy to displace the fossil fuels as our primary source of energy. Several materials are in the spotlight for its promising properties such as perovskites and chalcogenides. Among the available inorganic compounds, Cu-based chalcogenides are especially attractive for photovoltaic applications do to their potential to extend light harvesting into the near infrared region of the solar spectrum, their optical and electrical characteristics and large variety which includes earth-abundant, nontoxic and inexpensive elements. In this work, several routes for the synthesis of copper-antimony-sulfide/selenide compounds are explored such as ligand exchange, where organic fatty ligands that surround the surface of nanocrystals are removed and replaced by shorter inorganic ones

molecular inks, where bulk materials are dissolved in a thiol-amine mixture at low temperatures allowing a complete solution process fabrication

and cation exchange, which is a post-synthetic strategy for the fabrication of ionic nanocrystals that allows the total or partial replacement of host cations in the lattice of a pre-synthesized parent system. Herein, the whole process of the solar cell is covered: Synthe-sis, characterization and fabrication. The most remarkable finding in this work is the effect of the volume change (ΔV) in the crystal structure between the parent nanocrystal and the final composition on the morphology of cubic berzelianite Cu2-xSe nanoparticles while inducing partial cation exchange with Ge4+ and Sb3+. We found that in the case of Ge4+(ΔV 11.3%), the nanoparticles’ size and shape remained basi-cally the same, but when CE with Sb3+ was performed, monocrystalline nanoplates of around 200 nm were obtained. We observed that when Sb3+ goes inside the lattice of the Cu2-xSe nano-particles, it triggers a reorganization of the anion framework because of the high stress induced in the lattice. As these metastable nanoparticles gain energy as Sb3+ continues to substitute Cu+ ions, the nanoparticles start to orient and attach as a way to reduce their surface stress and en-ergy, thus forming the nanoplates. This new approach for growing larger crystals can help to overcome the limitations of small nanoparticles and to broaden even further the sea of possibili-ties to synthesize more and more complex materials.