Surface Passivation with a Fluorocarbon-Based Pyridine Derivative for High-Crystallinity Perovskite Solar Cells with Efficiency Over 20% and Good Humidity Stability

Abstract

Organic–inorganic hybrid perovskite solar cells (PSCs) are presently gaining significant attention owing to their high conversion efficiencies achieved in recent years. However, poor long-term stability against water and defects at film surfaces and grain boundaries are important factors causing performance degradation and rapid loss of the photovoltaic response. To remedy this, a pyridine derivative with long C–F chains (PFAD) is synthesized and employed as a passivator to reduce the trap states of perovskite and promote better humidity stability via antisolvent properties. The results demonstrate that the trap states of perovskite could be minimized by the presence of pyridinic nitrogen and then the formation of coordination bonds with undercoordinated Pb2+ ions. The resulting carrier recombination time is prolonged and verified via photoluminescence. The power conversion efficiency (PCE) of the PFAD-passivated perovskite solar cell increased to 20.48%, with practical elimination of hysteresis due to the high quality of the perovskite films. The significant gain generated via PFAD modification supports further applications in thin-film optoelectronic devices. Moreover, PFAD-modified devices exhibit enhanced humidity stability due to the protection of hydrophobic C–F chains from moisture; the PCE decreased about 15% after 30 days of exposure in a moisture ambient condition. Our work provides a promising strategy to further improve the performance and stability of perovskite solar cells by designing bifunctional organic molecules with passivation and hydrophobic effects.