Interfacial engineering of potassium-assisted Fe2O3 electron extraction layer for efficient and stable perovskite solar cells

• Fe 2 O 3 -KCl as an electron extraction layer improved perovskite solar cell efficiency to 15.29%, a 27.6% increase over pristine Fe 2 O 3 . • Devices with Fe 2 O 3 -KCl retained 78% of their initial efficiency after 1000 hours of operation, compared to 66% for control devices. • The Fe 2 O 3 -KCl layer reduced recombination losses, leading to a higher J SC of 21.89 mA/cm 2 and a V OC of 1.03 V. • Potassium ions facilitated defect passivation and grain growth, extending carrier lifetimes and reducing trap density by 25%. Perovskite solar cells (PSCs) continue to face performance limitations arising from interfacial defects and instability. This work presents a potassium-assisted hematite (Fe 2 O 3 -KCl) electron extraction layer (EEL) as a simple yet effective interfacial engineering strategy to enhance charge extraction and device durability. The incorporation of KCl into the Fe 2 O 3 layer promotes uniform perovskite crystallization, induces a continuous columnar grain structure, and significantly reduces interfacial trap density (from 4.26 × 10 15 to 3.19 × 10 15 cm -3 ), collectively improving charge transport and suppressing non-radiative recombination. The optimized Fe 2 O 3 -KCl device achieves a power conversion efficiency (PCE) of 15.29%, showing a 27.6% enhancement over pristine Fe 2 O 3 -based cells, with strong agreement between J-V and EQE-integrated current densities. Photoluminescence, TRPL, TPV, and SCLC analyses confirm accelerated charge extraction and prolonged carrier lifetime due to effective K + /Cl - mediated defect passivation. The modified devices also exhibit improved operational stability, retaining 78% of initial PCE after 1000 hours of continuous AM1.5G illumination inside a nitrogen glovebox, compared to 66% for the control. These results demonstrate that KCl-modified Fe 2 O 3 serves as a promising, low-cost, scalable EEL for next-generation PSCs by simultaneously enhancing efficiency and long-term operational robustness.