An Arginine-Doped Cathode Interlayer Enables Enhanced Efficiency in Organic Solar Cells

The appearance of the cathode interlayer (CIL), a transition bridge between the cathode and the organic photoactive layer (OPL), provides a new pathway for the performance improvement of organic solar cells (OSCs). PFN-Br is widely employed in many optoelectronic devices, including nonfullerene OSCs, to transport electrons and improve charge injection at the interface. However, due to the relatively low conductivity of PFN-Br, the thickness of the CIL prepared with PFN-Br is usually less than 10 nm, which evidently contradicts the requirements for large-scale roll-to-roll manufacturing. Herein, a strategy using N-alpha-carbobenzyloxy-d-Arginine (NA) as the doping material is proposed to improve the performance of PFN-Br. The homogeneous distribution of NA in PFN-Br can modify the work function (WF) of PFN-Br and facilitate an interface dipole arrangement that is favorable for charge transfer, resulting in binary CILs with a tunable WF and increased conductivity. To verify this method, a series of devices were prepared with PBDB-T:IT-M or PM6:Y6 as the OPL and different proportions of NA in the CIL. The use of PFN-Br:NA (0.75:0.06, in weight%) in devices helps to improve the OPL morphology, making it exhibit a trend of fiber network structure, leading to a higher fill factor and short circuit current density. Consequently, the optimal power conversion efficiency (PCE) based on the PBDB-T:IT-M and PM6:Y6 is increased from 10.5% to 11.1% and from 15.4% to 16.0%, respectively. In addition, the NA-doped device exhibits better nitrogen stability after 360 h of dark storage compared to the control. The discovery of these modification approaches provides insight into the hybrid cathode interlayers required for efficient and reliable nonfullerene OSCs.