A Printable Organic Cathode Interlayer Enables over 13% Efficiency for 1-cm2 Organic Solar Cells

Currently, most cathode interlayer (CIL) materials for organic solar cells (OSCs) cannot be processed by printing techniques, which severely limits their use in practical productions. Herein, we report a naphthalene diimide (NDI)-based small-molecular compound (N,N-dimethylamino)propyl naphthalene diimide (NDI-N) as printable CIL for OSCs. NDI-N exhibits a unique advantage that combines the merits of high crystallinity and good film-forming property in one material, endowing the semiconductor with excellent electron-transport properties and good processability. By using the NDI-N as CIL, a high power-conversion efficiency (PCE) of 13.9% was achieved in a PBDB-T-2F:IT-4F-based OSC device. More importantly, a large-area OSC device of 1 cm2 was fabricated by using the blade-coated NDI-N CIL and an outstanding PCE of 13.2% was achieved, which represents the highest efficiency of large-area OSCs. The results in this work may pave the way for low-cost and mass production of OSCs.