Dual-Phase Ligand Engineering Enables 18.21% FAPbI₃ Quantum Dot Solar Cells

Formamidinium lead triiodide (FAPbI₃) perovskite quantum dot (PQD) are promising candidate for high-performing quantum dot photovoltaic due to its narrow bandgap, high ambient stability, and long carrier lifetime. However, the carrier transport blockage and nonradiative recombination loss, originating from the high-dielectric ligands and defects/trap states on the FAPbI₃ PQD surface, significantly limit the efficiency and stability of its photovoltaic performance. In this work, through exploring dual-site molecular ligands, namely 2-thiophenemethylammonium iodide (2-TM) and 2-thiopheneethylammonium iodide (2-TE), a dual-phase synergistic ligand exchange (DSLE) protocol consisting of both solution-phase and solid-state ligand engineering is demonstrated. The DSLE strategy effectively replaces the native long insulating ligands and simultaneously passivate surface defects in hybrid FAPbI₃ PQDs, leading to enhanced electronic coupling for efficient charge transport. Consequently, the FAPbI₃ PQD solar cell based on DSLE strategy achieves a notable enhanced efficiency from 15.43% to 17.79% (2-TM) and 18.21% (2-TE), respectively. Besides, both 2-TM and 2-TE engineered devices exhibit enhanced stability, maintaining over 80% of its initial efficiency after aging in ambient environment (20-30% humidity, 25 °C) for over 1400 h. It believes these findings will provide a new protocol to precisely regulate the surface chemistry of hybrid PQDs toward high-performance optoelectronic applications.