Cost‐Effective Schiff‐Base Nickel Complexes as Cathode Interlayers for High‐Efficiency Organic Solar Cells

Abstract Efficient cathode interlayers (CILs) materials are crucial for high performance bulk‐heterojunction organic solar cells (BHJ‐OSCs). Herein, we report three excellent and low‐cost CILs Ni‐Me, Ni‐iPr, and Ni‐tBu based on Schiff‐base nickel complexes for the first time. The target molecules are obtained by highly efficient reactions and simple purification methods, affording a high overall yield of over 73%. These CILs show great work function tuning capability and film‐forming property. Among them, Ni‐Me demonstrates the highest electron conductivity (6.5 × 10 −4 S cm −1 ) and electron mobility (5.1 × 10 −4 cm 2 V −1 S −1 ), surpassing those of the widely used high‐performance CILs PDINN (5.2 × 10 −4 S cm −1 , 1.76 × 10 −4 cm 2 V −1 S −1 ), and PNDIT‐F3N (3.23 × 10 −5 S cm −1 , 2.64 × 10 −4 cm 2 V −1 S −1 ). Grazing incidence wide‐angle x‐ray scattering measurements indicate that Ni‐Me has higher crystallinity than Ni‐iPr and Ni‐tBu. When employed as the CIL in PM6:L8‐BO OSCs, Ni‐Me delivers a remarkable power conversion efficiency of 19.11%, outperforming PDINN (18.52%) and PNDIT‐F3N (18.5%). The Ni‐Me CIL also shows excellent universality (19.06% for PM6:BTP‐eC9 and 19.62% for D18:L8‐BO). This work demonstrates that Schiff‐base nickel complexes have great potential as CILs in OSCs.