Mrs. Jenia Vinokur, PhD. Candidate
The fundamental structure of all organic electronic devices is a stack of thin layers, sandwiched between electrodes, with precise layer morphology and interlayer interactions. Solution processing multilayers with little to no intermixing is, however, technically challenging and often incompatible with continuous roll-to-roll, high-speed manufacturing. Recently, our group demonstrated the spontaneous generation of cathodic interlayers by migration of additives to the organic/metal interface during the metal evaporation. The new method utilizes additive–metal chemical affinity as the driving force for additive migration from within the active layer toward the metal electrode to form an interlayer. Here we study the buildup of the interlayer and its effect on the interfacial work function in two fundamentally different organic photovoltaic systems and five different ethylene glycol oligomer additives. We find that regardless of system and additive type, Voc increases with additive concentration until a saturation value following a Langmuir isotherm-like behavior. This correlation suggests that, although the additives migrate from within and through the solid film, the interlayer buildup could be described by the adsorption of additive molecules to sites on the metal surface. The sites are independent, equivalent, and can have unit occupancy, and the adsorbate additive molecules are immobile on the surface. Under such conditions, the fractional occupancy of the adsorption sites, i.e, the degree of coverage, determines the Voc and hence device performance.
Advisor: Prof. Gitti Frey
Seminar via ZOOM