Bi-synergistic ligand-mediated passivation of surface defects for highly efficient and stable cesium-lead-iodide perovskite quantum dot photovoltaics

Abstract

Perovskite quantum dot (PQD) photovoltaics (PVs) integrated with ZnO nanoparticle (NP)-based electron transport layers (ETLs) are a promising technology because of their favorable energy-level alignment and solution-process compatibility. However, severe surface defects, including undercoordinated Pb²⁺/I⁻ vacancies on the PQDs and O vacancies/residual hydroxyls on ZnO, trigger performance degradation pathways (e.g., surface recombination and ion migration). To address this, in the present study, a bifunctional ligand, i.e., 4-(trifluoromethyl)benzylamine (TFMBA), was designed to concurrently passivate the CsPbI₃ PQD film and the ZnO NP film via coordination (amine–Pb²⁺/Zn²⁺) and hydrogen-bonding interactions (amine–I⁻/OH⁻). This unified strategy achieved a 61% reduction in the trap density (i.e., (3.76 ± 0.20) × 10¹⁵ cm⁻³ w/o passivation and (1.66 ± 0.10) × 10¹⁵ cm⁻³ w/passivation), enhancing charge extraction in PQD PVs. The device achieved a power conversion efficiency (PCE) of 14.5% ± 0.2% under 1-sun conditions (vs. 13.0% ± 0.3% control) and 40.6% ± 0.2% under 1000-lx LED illumination (vs. 37.2% ± 0.7% control). Furthermore, the TFMBA-treated device retained 92% of its initial PCE after 500 h (20–30% relative humidity), demonstrating excellent ambient stability. This study demonstrates that dual-surface passivation using a multifunctional ligand is effective for achieving high-performance PQD-based optoelectronic devices.