SIZE FOCUSING APPROACH OF HIGH CONCENTRATION CU2-XS NANOPARTICLES AND SCALABLE SYNTHESIS METHODOLOGY OF PURE PHASE COPPER TIN SULPHIDE

Abstract

Nanoparticles and their size-dependent properties have long since revolutionized the technological industry from the way engineers conceptualize and design modern devices to the way scientists understand the underlying physics and its potential implications. Intricate control on the sizes of semiconductor nanoparticles results in profound control over the bandgap making absorptions and emissions increasingly efficient. However, synthesis of scalable amounts of size focused nanoparticles remain the biggest challenge in the industry. A polydisperse distribution of sizes corresponds to a variation in its properties which nullifies the primary motivation for using nanoparticles. Moreover, for nanoparticles to become a standing competitor in the semiconductor industry, there is a need to establish synthesis procedures compatible with scalable large-scale nanoparticle manufacturing without undermining their crucial dimensional influence. These procedures are prey to a wide variety of parameters starting from the preliminary salts, their chemical interactions to physical stimulus making optimization of each material on a large scale all the more difficult. We substantiate this need with a nanoparticle reusability concept wherein any batch of polydisperse particles can be transformed to a size tuned group with the help of an etchant (Oleylamine or Chlorine) and re-grown with heat-up technique. This post synthesis treatment enables the use of large-scale synthesized particles and tune their sizes corresponding to the desired application. In this thesis, we were successful in tuning the size to 8.5nm with a dispersity of 7%. The etchant is used to decrease the size variation in the polydisperse batch and produce monomers. Monomer saturations, in turn, combat competitive growth or Ostwald ripening and instead help the larger particles to grow uniformly when heated up. Our investigations are heavily concentrated in the Cu2-xS system which is viewed as a practical substituent to other toxic counterparts like Cadmium or lead-based semiconductor nanoparticles. Understanding this system forms a conceptual foundation for manipulating related ternary and quaternary compounds like Copper-Indium-Sulphide(CIS) or Copper-Tin-Sulphide(CTS) which have a host of applications of their own. We also elucidate a method of utilizing high concentration scalable production to create phase pure batches of Mohite CTS. These particles exhibit band gaps ranging from 1.04eV to 1.38eV which is suitable to most optoelectronic applications like solar cells and photodetectors. Future work would be to extend the particle reusability to other systems, investigate the influence on associated ternary and quaternary compounds thus probing a step closer in making this approach acceptable commercially. Furthermore, creating devices from these size tuned particles and reviewing any improvements would exhibit great progress in the study of copper-chalcogenide nanoparticles and their potential in the industry.