A novel perylene diimide-based ionene polymer and its mixed cathode interlayer strategy for efficient and stable inverted perovskite solar cells

Abstract

Inverted (p–i–n) perovskite solar cells (PerSCs) have attracted much attention owing to their low temperature processability, less hysteresis effect and easy integration as a subunit for the tandem device. The unsatisfactory interface contacts and energy level barrier between adjacent interlayers on the cathode side are one of the key challenges for the development of p–i–n PerSCs. Herein, perylene diimide-based (PDI) ionene polymer was synthesized and developed as a cathode interlayer (CIL) to enhance interface contact, reduce the energy level barrier and prevent the migration of I- ions. The compact PNPDI CIL with high conductivity and appropriate lowest unoccupied molecular orbital (LUMO) level, resulted in a high efficiency device (20.03%), which is higher than the control device with bathophenanthroline (Bphen) (19.48%). Bphen-based CIL shows better adjusting ability of the work function of cathode metal but exhibits poor film-forming property. So, the synergistic effect of 1 + 1 > 2 can be obtained by combining Bphen and PNPDI into one CIL. As expected, the device performance was further improved by using the mixed CIL of Bphen and PNPDI, and 21.46% power conversion efficiency (PCE) was achieved. What’s more, the compact and hydrophobic mixed CIL dramatically enhanced the resistance to I- ions and moisture, which led to much enhanced device stability.