Vacuum-assisted reforming cathode interlayer orientation for efficient and stable perovskite solar cells

The cathode interlayer (CIL) is vital for enhancing the performance of inverted (p-i-n) perovskite solar cells (PSCs) by preventing charge recombination and ion diffusion, thereby achieving superior efficiency. Herein, we introduce cost-effective perylene-diimide (PDI)-based CILs—PDIN-S, PDIN, and PDIN-L—with varying spacer lengths. Among them, PDIN-S exhibits exceptional attributes in thermal evaporation processability, optical absorbance, and charge transfer capabilities. Molecular orientations of PDIN-S are studied through two deposition techniques: vacuum thermal evaporation (VE) and spin-coating (SC). The face-on orientation observed in PDIN-S (VE) confers significant advantages, including improved π–π stacking, efficient charge carrier transfer, reduced interfacial resistance, and inhibited ion diffusion. Furthermore, PDIN-S (VE) also lowers the energy barrier towards cathode, boosting PSC efficiency to 23.82%. Moreover, it enhances both thermal and light stability, maintaining over 90% initial efficiency for 2036 h at 85 °C and sustaining 80% efficiency for 1848 h under continuous illumination. Our application of a straightforward VE method enables the manipulation of molecular orientation, resulting in a concurrent enhancement of efficiency and stability. These findings underscore the potential of PDIN-S as a promising component for highly efficient and stable PSCs.