Guideline for Efficiency Enhancement in Semi‐Transparent Thin‐Film Organic Photovoltaics with Dielectric Mirrors

Abstract

Semi‐transparent organic solar cells (ST‐OSCs) show a unique potential to be integrated in windows due to their outstanding characteristics such as high transparency and color‐adjustability. In order to achieve both, high transparency and high efficiency, the use of dielectric mirrors is an excellent concept. However, such a mirror will not only improve the photocurrent generated by a solar cell but also cause losses in transparency. In this work, a theoretical model is developed that predicts the effect of the dielectric mirror on the balance between photocurrent enhancement and transparency loss depending on the spectral shape of the ST‐OSC absorption. Experimental investigations with three fully printed ST‐OSCs showing different absorption characteristics underline the validity of these studies. It is concluded that ST‐OSCs with broad absorption spectra ranging from the short wavelength region over the visible to at least 950 nm are most suitable for the implementation of a dielectric mirror. A narrower absorption spectrum or a shift of the spectrum toward longer wavelengths makes an increase in photoactive layer thickness more beneficial than the attachment of a dielectric mirror. Moreover, the dielectric mirror approach is an excellent strategy to obtain high photocurrents for materials which cannot be processed at high active layer thicknesses.