Optical and electrical losses in semitransparent organic photovoltaics

Semitransparent organic photovoltaics (STOPVs) allow for low-cost, sustainable, and integrated energy harvesting solutions. To promote STOPVs to reach the theoretical limit efficiency, it is necessary to clarify the optical and electrical losses during the transition from opaque to semitransparent devices. In this paper, we first calculate the photon and photocurrent losses of STOPVs relative to opaque devices and demonstrate the presence of additional current loss in STOPVs. Then, a quantitative analytical model is used to assess the current loss and charge recombination processes in STOPVs. Capacitance spectroscopy is used to decouple the recombination current densities in STOPVs to bimolecular, bulk-trap-assisted, and surface-trap-assisted components. As the thickness of the silver electrode reduces, the devices show lower Langevin prefactors, comparable bulk trap densities, and significantly increased surface trap densities, indicating that surface-trap-assisted recombination is the main current loss pathway in STOPVs.