Simultaneous cationic–anionic site modulation via guanidinoacetic acid for defect passivation in high-efficiency and stable perovskite solar cells

Abstract

Most passivation strategies in perovskite solar cells rely on toxic additives or selectively target either cationic or anionic defects, leaving complementary defect states insufficiently addressed. Achieving simultaneous control over both defect types using environmentally benign additives is essential to suppress non-radiative recombination and enhance device stability and performance, yet remains a significant and insufficiently addressed challenge. Here, we introduce a simple and effective strategy by incorporating guanidinoacetic acid (GAA), a low-cost and biocompatible zwitterionic molecule, as a passivating agent. It contains a positively charged guanidinium group (NH2–C(=NH2 +)–NH–) and a negatively charged carboxylate group (COO− ), enabling simultaneous dual-site defects passivation in perovskites. X-ray photoelectron spectroscopy reveals a 0.16 eV shift in Pb 4 f binding energy with suppression of metallic Pb⁰ , alongside a 0.15 eV shift in I 3d peaks, confirming strong chemical interaction and defect passivation. This dual interaction effectively suppressing electron trap-state density from 3.29 × 1015 cm− 3 to 2.41 × 1015 cm− 3 , and hole trap-state density from 4.06 × 1015 cm− 3 to 3.53 × 1015 cm− 3 , and promotes the formation of highly crystalline films with enlarged grains (612 nm for GAA versus 398 nm for the control). The resulting films exhibit markedly suppressed non-radiative recombination, evidenced by prolonged carrier lifetimes from τ1 = 196.1 ns and τ2 = 1880 ns (control) to τ1 = 271.3 ns and τ2 = 2951 ns (GAA). Consequently, GAA-passivated devices achieve a power conversion efficiency of 22.65% with reduced-hysteresis, significantly outperforming control devices (18.85%), while also demonstrating enhanced environmental stability, retaining 86% of their initial efficiency after 500 h under continuous illumination at 25°C and 35–50% relative humidity. These results establish biocompatible zwitterionic molecule dual-site passivation as a robust and sustainable strategy for concurrently improving the efficiency and operational stability of perovskite solar cells.