Dual-anchor interface engineering with a phosphonic acid modifier for improving perovskite solar cell performance

Solution-processed planar SnO₂ electron transport layers (ETLs) fabricated <i>via</i> sol-gel methods offer promising scalability for manufacturing perovskite solar cells (PSCs). However, inherently, interfacial defects at both the SnO₂ surface and the perovskite buried surface severely degrade device performance. Interface engineering of SnO₂ ETLs using molecular modifiers presents a promising pathway toward high-performance PSCs. In this work, we propose a dual-functional interface engineering strategy employing aminomethylphosphonic acid (AMPA), an amphiphilic molecule featuring complementary -NH₂ and -PO₃H₂ functional groups, to simultaneously regulate charge transport dynamics and crystallization kinetics. The phosphonic acid group is firmly bound to the surface of SnO₂, which effectively suppresses the surface carrier trap and leakage current and makes the surface potential uniform. At the same time, amino groups affect the growth of perovskite films, resulting in higher crystallinity, phase purity, and fewer defects. In addition, open-circuit photovoltage attenuation analysis (OCVD) tests show that the ion aggregation phenomenon of the device is weakened and ion migration is inhibited. TPC indicates a shortened recovery time constant, which may be due to reduced band bending at the interface, resulting in increased mobility of electron injection energy barriers. As a result, the PCE increased from 18.95 to 20.47% while exhibiting excellent stability.