2, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Organic photovoltaics (OPVs) have attracted major attention over the last two decades for their potential as a cheap, renewable energy technology with unique application potential unavailable to traditional inorganic technologies. Key to the development of this technology has been an understanding and control of the thin film, bulk heterojunction morphology from the molecular to mesoscale. To yield efficient devices, charge carriers must be quickly extracted from the active layer after generation, but in a competing process, oppositely charged carriers can meet and recombine. In high performance devices, the bimolecular charge recombination process represents the dominant loss mechanism and further mitigating this loss is one of the major avenues toward continued performance improvements. However, rational chemical, formulation, and processing design to both maximize the extraction rate and minimize the recombination rate has been difficult due to gaps in fundamental understanding of which factors impact each competing process.
In this talk, I will highlight recent efforts to develop an impedance-based experimental method for quantifying the charge transport and recombination behavior in real devices under operating conditions with high accuracy. I will then demonstrate how this technique can be used to provide a detailed quantification of how various fabrication process parameters impact the detailed device performance characteristics. Integrating this fabrication and measurement data into a broader OPV recombination measurement database, I will demonstrate how improved data collection and availability allow the statistical analysis of competing device models and the discovery of new trends. With increased adoption of this technique and data sharing, machine learning techniques could produce improved models that capture the complex processing-structure-property relationships and accelerate the discovery and development of new materials for OPVs.
 M. C. Heiber, T. Okubo, B. Luginbuhl, and T.-Q. Nguyen, “Measuring the Competition Between Charge Extraction and Recombination in Organic Solar Cells under Operating Conditions” (In Preparation)