Correlating the Photoshunt with Charge-Collection Losses in Organic Solar Cells

The low charge carrier mobility of molecular materials is one of the key obstacles to achieving higher efficiencies in organic photovoltaics. Therefore, understanding and quantifying charge collection losses owing to low mobility is an important challenge in organic photovoltaics and other emerging photovoltaic technologies. Here, an approach is proposed to use the photoshunt and its dependence on light intensity as an easily accessible indicator of charge-collection losses. The physical meaning of the photoshunt is explored using drift-diffusion simulations and an analytical model. The results show that the recombination current visible as the photoshunt is decreasing with increasing charge carrier mobility. Furthermore, a framework is presented for evaluating the short-circuit current losses in experimental data using a photoshunt. The study reveals that the charge-collection efficiency at shortcircuit is strongly influenced by the charge carrier mobility and light intensity.