Molecular doping with 4-aminobenzylphosphonic acid for stable and efficient inverted perovskite solar cells

Long-term stability continues to be the primary obstacle for the widespread industrialization of cost-effective perovskite solar cells (PSCs), in spite of remarkable achievements in their efficiency. Molecular doping in polycrystalline perovskites is a feasible strategy to enhance device stability without sacrificing efficiency by improving film quality and optimizing interfacial properties. Herein, we report a functional 4-aminobenzylphosphonic acid (ABPA) molecular doping approach to improve perovskite film quality, as well as the critical performance parameters and device stability in inverted PSCs. The perovskite film incorporating ABPA exhibits a compact surface morphology, lower roughness and defect density, improved crystallinity, well-aligned energy levels, and reduced non-radiative recombination, resulting from the versatile intermolecular interactions between ABPA and the perovskite precursor species. The coordination bonding between the phosphonate groups (-PO₃H₂) and undercoordinated Pb²⁺ ions, as well as the hydrogen bonding between the amine (-NH₂) moiety and formamidinium/halides, has been comparatively investigated. Consequently, the optimal device based on the ABPA-doped perovskite film delivered a power conversion efficiency of 23.81% (certified 22.94%). Furthermore, the unencapsulated ABPA-modulated device retained 95% of its original efficiency after being stressed under continuous exposure to 1 sun equivalent illumination at 50 °C in a nitrogen (N₂) environment with maximum power point tracking for 2000 hours.