Evolution of light absorption and emission characteristics of organic perylene nanoparticles through hydrothermal process: Application to solar cells

The evolution of the structural and optical characteristics of polymorphic organic perylene nanoparticles (NPs) is demonstrated by controlling the π-π interactions using a hydrothermal process. The light-emission colors of the perylene NPs vary gradually from yellow to green to light blue with increasing hydrothermal temperature from 110 to 160 °C. An enhanced crystallinity of the NPs from 110 °C to a critical temperature T_c of 140 °C and a transition to the amorphous phase above T_c are observed. The evolution of the photo-luminescence (PL) and optical-absorption characteristics in terms of variations in the crystallinity and physical dimensions (size and shape) of the perylene NPs resulting from the hydrothermal process are analyzed. These results are confirmed by nanoscale PL measurements for single NPs using laser confocal microscopy. The photovoltaic characteristics of organic solar cells (OSCs) are improved through the use of the perylene NPs. It is found that the performance of the OSCs is strongly correlated with the optical-absorption properties of the perylene NPs.