Stable, conductive, and cost-effective semi-transparent electrodes for organic photovoltaics and beyond

Transparent conductive electrodes (TCEs) are a special class of material, as they are both transparent and conductive. In reality, however, these two important characteristics typically trade-off with one another and thus must be balanced. In terms of the material system, the selection of the TCE with the best performance is essential, which is evaluated by the so-called “figure of merit” (FOM). Hence, researchers have suggested various FOMs to rate the TCEs over the past 50 years. However, a more straightforwardly formulated FOM may help to assess a TCE's potential specifically for photovoltaic applications. Since the requirements for the latter are distinctly different compared to other optoelectronic devices, this thesis is devoted to bridging this gap. A novel and exact FOM is proposed that exclusively quantifies the impact of the TCE on photovoltaic performance. This exact FOM fulfills the aspired requirement of being a normalized, dimensionless, and proportional factor for the potential photovoltaic output power with respect to the Shockley-Queisser limit. Using this FOM, a set of current state-of-the-art semi-transparent electrodes is comprehensively assessed, where the spectral range in which photovoltaic materials operate is an important factor. Based on a comment from a colleague at the National Renewable Energy Laboratory, the exact FOM is extended into formulations that allow the assessment of different solar module geometries, including the addition of serial connections and additional metal grids. The thesis also includes a thorough study of the impact of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) processing conditions on its work function. Various formulations are tested with regard to relative humidity levels, annealing temperatures, and solar cell performance. Finally, literature assessments and strategies for achieving highly conductive PEDOT:PSS TCEs are conducted at the end of the thesis.