Utilizing Wide Band Gap, High Dielectric Constant Nanoparticles as Additives in Organic Solar Cells

We experimentally and theoretically investigate the effects of utilizing BaTiO3 nanoparticles as additives in polythiophene/fullerene solar cells. BaTiO3 nanoparticles were chosen because of their multifaceted potential for increasing exciton dissociation (due to their high dielectric constant) and light scattering. To achieve stable suspensions for device fabrication, the nanoparticles were functionalized with organic ligands. Solar cells fabricated in air showed ∼40% enhancement in the photocurrent primarily due to string-like aggregates of functionalized BaTiO3 particles that increase light absorption without hindering charge collection. Solar cells fabricated in an inert atmosphere yielded overall more efficient devices, but the string-like aggregates were absent and enhancement in photocurrent was up to ∼6%. Simulations with the excitonic drift-diffusion model demonstrate that a bare nanoparticle significantly increases exciton dissociation, whereas the functional group negates this effect. Simulations utilizing the scattering matrix method reveal that absorption enhancements caused by light scattering increase as the nanoparticles aggregate into string-like structures. These results offer insights for morphological design of ternary-blend bulk-heterojunction organic solar cells.