Electric‐Induced Degradation of Cathode Interface Layer in PM7:IT‐4F Polymer Solar Cells

Cathode buffer layer interface modification is a commonly used strategy to prepare high‐efficient organic solar cells (OSCs). Nonfullerene OSCs based on PM7:IT‐4F are prepared and modified with poly[(9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] (PFN)‐Br cathode buffer layer. The introduction of the PFN‐Br buffer layer obviously boosts the photovoltaic performance of PM7:IT‐4F‐based OSCs, however, the stability of the PFN‐Br‐modified device shows a serious degradation. By excluding the influence of heat, oxygen, moisture, and light illumination, the degradation is verified to be triggered by the electric effect. As soon as the devices undergo electrical measurement such as applying a bias voltage for the current density–voltage test, the degradation begins. The degradation mechanism of the PFN‐Br‐modified OSCs is investigated in detail with intensity modulated photovoltage spectroscopy/photocurrent spectroscopy (IMPS/IMVS), photoinduced charge extraction linear increasing voltage (Photo‐CELIV), and impendence spectroscopy (IS) technology. The results show that the PFN‐Br cathode buffer layer is deteriorated and increases the interface resistance between active layer and cathode, which hinders charge transport and collection at the electrode, thus weakening the performance of PM7:IT‐4F‐based OSCs. The degradation of PM7:IT‐4F/PFN‐Br OSCs induced by the electric effect proposed herein provides a new inspiration for the degradation study of OSCs.