| The growing global demand for energy and increased concerns with the environmental impacts of fossil fuel consumption necessitates an emphasis on developing renewable energy technologies. Due to the abundance of solar energy, photovoltaics are a promising renewable energy technology. However, traditional photovoltaic technology is largely based on silicon, which is inflexible, requires expensive processing, and involves heavy equipment for sealing and mounting. Solution-processed organic photovoltaics (OPVs), on the other hand, have the potential to be a cost-effective, renewable energy source due to their amenability to high-throughput roll-to-roll processing, earth-abundant constituents, and architectural tunability over multiple length scales. Nonetheless, a major challenge for OPVs to attain widespread implementation is to advance the power conversion efficiencies (PCEs) from recently certified and impressive values of 11.5% to ≥ 15%. Strategies to enhance BHJ OPV performance include developing new low bandgap polymeric donors having broad optical cross-sections and high carrier mobility.;Emerging and promising alternatives to polymeric OPV donors are small molecule donors, offering the attraction of more straightforward synthesis and purification, less batch-to-batch variation in properties, and intrinsic monodispersity. Yet, compared to polymeric donors, solution-processable molecular donors have not been extensively investigated and the resulting devices have yielded lower PCEs. These observations raise the intriguing question of what new, photon-efficient OPV donor molecules might inform us about structure-response relationships and what new strategies need to be developed to improve device performance.;This thesis will present the design and development of a novel class of small molecule donors based on the electron donating moieties acenedithiophene and the electron accepting moieties diketopyrrolopyrrole, the performance optimization of OPV devices, thin-film morphology characterization, and the resulting structure-response relationships. These investigations give insights into the performance limitations that small molecule OPVs suffer from and ultimately provide methods for improvement. The insights provided herein could help lead to the development of more efficient small molecule solar cells, which will help the field of OPVs edge closer to commercial viability. |
