Experimental and theoretical investigations of charge generation and transport in thin film photovoltaics

With concerns regarding climate change, pollution, and a limited supply of fossil fuels, photovoltaics are an attractive alternate energy source. Within the field of photovoltaics, thin film organic solar cells are alluring due to their potential low cost, mechanical flexibility, and ease of fabrication. However, there are many drawbacks that need to be overcome such as incomplete photon absorption, incomplete exciton dissociation, and carrier recombination. Three distinct projects addressing charge generation and collection in thin film photovoltaics are described. The first details the use of microlens arrays (MLAs) as a nonintrusive method to increase photon absorption in organic solar cells. Laser holography and soft lithography were used to produce the MLAs on the glass side of an indium tin oxide substrate. In PTB7-based devices, we saw improvements in short circuit current (Jsc) of more than 10%, and achieved a high average power conversion efficiencies of 8.5%. Additionally, we used simulations utilizing the scattering matrix method to corroborate our experimental results. These simulations revealed that, for a given pitch of a MLA, a taller height typically yields more enhancement. Second, the effects of using BaTiO3 nanoparticles as additives in polythiophene:fullerene solar cells are experimentally and theoretically investigated. BaTiO3 nanoparticles were chosen because of their high dielectric constant, which can increase exciton dissociation, and the potential for 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, which increase light absorption without hindering charge