Degradation through Directional Self‐Doping and Homogeneous Density of Recombination Centers Hindered by 1,8‐Diiodooctane Additive in Non‐Fullerene Organic Solar Cells

Non‐fullerene‐based organic solar cells (OSCs) have recently proven to perform with efficiencies above 18%. This is an important milestone for one of the most promising technologies in the fields of flexible and transparent/semitransparent photovoltaics. However, the stability of OSCs is still a challenging issue to meet the industry requirements. Herein, several devices with IT‐4F:PM6 as the active layer with and without 1,8‐Diiodooctane (DIO) additive are characterized before and after a 1400 h degradation test under 1 sun white light‐emitting diode (LED) illumination intensity. The optoelectronic study via impedance spectroscopy under illumination at quasi‐open‐circuit correlates the use of DIO as an additive with a retarded degradation behavior and an overall improved device performance. In dark conditions, the Mott–Schottky analysis suggests that samples without DIO develop self‐doping during degradation, changing the p‐i‐n doping profile into a p–n type, most likely related to the evolution of the blend demixing. These mechanisms are further confirmed by drift‐diffusion simulations. Space‐oriented redistribution of shallow trap levels (self‐doping) and homogeneous increase in deep‐trap levels (nonradiative recombination) are shown to be hindered by the use of the DIO additive.