One-step synthesis of low-cost perylenediimide-based cathode interfacial materials for efficient inverted perovskite solar cells

Interface engineering plays an important role in improving the performance of perovskite devices. Herein, we reported two perylenediimide small molecular cathode interface materials (CIMs), PDI-2N and PDI-4N, synthesized by a simple method and with good alcohol soluble, which could be used as cathode interfacial layer (CIL) for high-performance inverted perovskite solar cells (PVSCs). The PDI-4N exhibits larger electrical conductivity, electron mobility and self-doping properties than PDI-2N because of more dimethylamino functional groups in the amide positions. Based on these superiorities, a peak PCE of 21.33% with PDI-4N as CIL was achieved, which is the highest PCE for PDI-based interlayer materials as the cathode interlayer in inverted PVSCs. While the PCE with PDI-2N as CIL is only 17.41%. The significant improvement in device efficiency for PDI-4N based device is due to reduced defect density, lower dark current, larger recombination resistance and better surface morphology, which improved charge transport and collection at the PC₆₁BM/Ag interface. Moreover, the ambient stabilities of PVSCs with PDI-2N and PDI-4N as CIL show that the CILs can effectively improve the device stability, and good stability with a PCE loss of only ∼3.0% after 600 h is also obtained. In a word, this work will provide us with molecular design approach by one-step to develop novel cathode interface materials with functional side chains for high-efficiency PVSCs.