Characterization of mechanically synthesized AgInSe2 nanostructures

Abstract

A quantum dot (QD) solar cell is an emerging field in solar cell research that uses QDs as the photovoltaic material. QDs have band gaps that are tunable across a wide range of energy levels by changing the QD size. Embedding different sized dots within the absorbing layer encourages harnessing the maximum spectrum energy. Also, other effects like a very high surface to volume ratio and quantum transport make them attractive for future devices. AgInSe2 (AIS) nanoparticles with tetragonally distorted phase have been prepared by mechanically alloying the synthesized bulk AIS powder at room temperature in a planetary ball mill under Ar in an attempt to create QDs. Nanoparticles are formed of ∼10 nm in size. These ball-milled nanoparticles contain different shapes and the Rietveld analysis of X-ray powder diffraction data reveals their detailed structural features. High resolution transmission electron microscope images also detect the presence of the tetragonal phase in ball-milled samples. Peak broadening (full width at half maximum), the main characteristic of a decrease in size, is observed. X-ray diffraction data reveals the downscaling of crystallite from 103 to 7 nm, and the tetragonally distorted structure of the system was not disturbed by milling. Differential scanning calorimetric study also reveals the phase evolution and crystallization kinetics. Bulk samples show endo melting peak at 134 and 220 °C. The cooling–crystallization complexity of the peaks signifies that crystallization from melt was heterogeneous nucleation and crystallization from multiple types of centers. Unlike this milled samples show two crystallization effects at approximately 135 and 380 °C. Optical properties investigated to find band edges suggest that it is around 1.3 eV, which is encouraging for photovoltaic applications.