Ion-Pair Induced Electrostatic Gating at Buried Interface for Efficient, Stable, and Eco-Safe Perovskite Solar Cells

The commercialization of perovskite solar cells (PSCs) is severely limited by interfacial charge losses, poor stability, and lead leakage, with few strategies to address all issues simultaneously. We design 1,5-naphthalenedisulfonic acid sodium salt (NSA) as a multifunctional buried interface modifier for SnO₂-based PSCs. NSA features sulfonate groups, a rigid π-conjugated naphthalene backbone, and localized SO₃^--Na⁺ ion pairs, enabling an ion-pair-induced electrostatic gating effect beyond conventional chemical passivation: (i) sulfonate groups coordinate with undercoordinated Pb²⁺ defects to reduce trap density; (ii) the SO₃^--Na⁺ network generates a local electrostatic field to promote directional electron extraction and suppress hole backflow; (iii) the uniform NSA layer guides perovskite crystallization, producing larger grains and higher crystallinity. As a result, NSA-modified n-i-p PSCs reach a champion efficiency of 25.82%, with improved charge extraction and suppressed nonradiative recombination. Notably, the NSA layer acts as a robust lead-lock barrier, reducing lead leakage and boosting operational stability. This work presents a facile molecular design for buried interface engineering that synergistically optimizes efficiency, stability, and environmental safety in PSCs.