Engineering the hematite/perovskite interface with a PEAI interlayer to boost efficiency and operational stability

• PEAI interfacial layer effectively passivates surface defects at the α-Fe 2 O 3 /perovskite interface, reducing trap-assisted recombination. • Improved energy level alignment between α-Fe 2 O 3 and CsFAMA enhances electron extraction efficiency. • Enhanced perovskite crystallinity and film quality due to PEAI treatment, leading to larger grain size and fewer grain boundaries. • Suppressed non-radiative recombination losses, resulting in higher open-circuit voltage. • Stability improvement as PEAI provides a protective 2D-like layer against moisture and ion migration. Interface engineering is crucial for governing charge transfer dynamics and contributing to the prolonged operational stability of perovskite solar cells (PSCs). In this work, phenethylammonium iodide (PEAI) was introduced as an interfacial layer (IL) between hematite (α-Fe 2 O 3 ) and the perovskite absorber. This study represents the systematic investigation of PEAI as an ultrathin interfacial modifier for hematite electron transport layers (ETLs), addressing the key challenge of surface trap density and interfacial recombination at the α-Fe 2 O 3 /perovskite junction. A systematic optimization of PEAI concentrations (0–2 mg/mL) revealed that 1.5 mg/mL produced the most efficient device characteristics. The PEAI modification passivates surface traps on hematite, leading to a significant improvement in all photovoltaic (PV) parameters. Specifically, PEAI-treated devices exhibited increases in open-circuit voltage (V OC ) (1.09 → 1.11 V) and fill factor (FF) (69.13 → 73.08%), along with an 11.9 fold reduction in leakage current and a 25% decrease in trap-filled limit voltage. Compared with pristine devices, the optimized PEAI-treated PSCs showed a clear enhancement in current density–voltage (J–V) performance, with higher photovoltaic parameters, resulting in a power conversion efficiency (PCE) improvement from 14.49% to 15.86%. Long-term stability tests further revealed that the PEAI-modified devices retained 81% of their original PCE after 1000 h of continuous operation, while the pristine devices maintained only 64%. These findings demonstrate that PEAI is a highly effective passivation layer that improves both efficiency and stability, offering a promising strategy for advanced hematite-based PSC architectures.