Abhijit Gogoi

Atomistic modeling of nanoscale organic light-emitting diode.

This is a collaborative work with the experimental group of Prof. Chih-Jen Shih (Department of Chemistry and Applied Biosciences, ETH Zürich, Switzerland) where we reported the scalable fabrication of nanoscale organic light-emitting diodes (nano-OLEDs), with the highest array density (periodicity of 250 nm corresponding to 10^5 pixels per inch) and the smallest pixel size (~150 nm) ever reported to date. One of the most important component of nano-OLED is the emission layer (EML). In the present case, EML is composed of Tris(2-phenylpyridine)Iridium ((Ir(ppy)3)) and 4,4’-Bis(N-carbazolyl)-1,1’-biphynyl (CBP). We performed atomistic simulations to investigate the structure and dynamics of the EML. The EML is modeled as a spherical solid droplet which got equilibrated into a semi-spherical droplet on the graphene substrate. On this semi-spherical droplet, the Ir(ppy)3 molecules reside at the periphery of the droplet. This is an interesting and encouraging observation considering the fact that the exposure of Ir(ppy)3 molecules to the light source crucially impact the performance of the EML. With the decrease in size of the droplet, lesser number of CBP molecules surrounds the Ir(ppy)3 molecules. This suggests that smaller droplet will be more effective for LED applications. The size of the droplet also influence its dipole orientation. We have also computed the free energy change in bringing an Ir(ppy)3 molecule from the center of the droplet to the droplet-vacuum interface. From this, we observed that the preferential position of the Ir(ppy)3 molecules is the droplet-vacuum interface.