Meesha Kaushal

Meesha Kaushal
Dissertation Defense

Organic Photovoltaic Applications



Understanding exciton diffusion is a crucial step in engineering and fabricating organic photovoltaic (OPV) devices. We studied a variety of dyes in our lab including derivatives of carboalkoxyphenylporphyrins in solution-cast nanometer thick films. We established basic guidelines on how the exciton diffusion is affected by the arrangement and packing of peripheral alkyl groups in carboalkoxyphenylporphyrin solution-cast thin films. The overall goal of this work is to link the molecular organization to singlet exciton diffusion parameters. Photoluminescent (PL) lifetime decays (ts) and quenching efficiencies (Qeff) of solution-cast porphyrin thin films lightly doped with [6,6]-phenyl-C61-butryic acid methyl ester (PCBM) have been measured. This data has been used in a 3D exciton diffusion Monte Carlo eDiffusion simulation to generate the exciton diffusion parameters and nanocomposition in thin films. The length and branching of the peripheral alkyl groups in carboalkoxyphenylporphyrins influences the excited-state dynamics in a thin film. Using longer and symmetrical peripheral alkyl chains lengthens the PL decay lifetimes and exciton diffusion lengths (LD). Structural studies such as GIWAXS and XRD have indicated that molecular arrangement in longer and symmetrical peripheral alkyl chains leads to nematic packing on the surface of thin films which is favorable for exciton diffusion. Current-Voltage curves measured from ternary OPV devices fabricated using these carboalkoxyphenylporphyrins along with poly-3-hexylthiophene (P3HT) and PCBM also supports our previous exciton diffusion studies. Porphyrin derivatives with longer PL decay lifetimes (ts) and exciton diffusion lengths (LD) have shown higher photocurrents and improved power conversion efficiencies. Our findings are an important step toward a deeper understanding of the exciton diffusivity and molecular packing relationship.

Sponsoring Chair: Dr. Michael Walter

Defense Date: Wednesday,  April 10, 2019 at 11:00 AM