Optical and photovoltaic properties of organic solar cells versus bulk-heterojunction morphology

It has long been argued that the performance of organic bulk-heterojunction solar cells critically depends on the morphology of the active layer, a mixture of donor and acceptor materials in which the charge generation from sunlight occurs. In this work, optical homogenization principles are utilized to model the structure of the common active layer PM6:Y6. By systematically modifying the size and shape of Y6 acceptor inclusions within the morphology, we explore how these changes influence the refractive index and extinction coefficient of the resulting effective medium. A synergy of transfer matrix optical simulations with the Hecht equation is used to evaluate the effect of the inclusions features on the external quantum efficiency spectrum. The reported findings can be particularly helpful in the fabrication of similar classes of organic solar cells by indicating which aspects of active layer mixture may undermine the expected performance of the photovoltaic cells.