Tuning the Interfacial Dipole Moment of Spacer Cations for Charge Extraction in Efficient and Ultrastable Perovskite Solar Cells

The two-dimensional (2D)/three-dimensional (3D) heterojunction perovskite solar cell (PSC) has recently been recognized as a promising photovoltaic structure for achieving high efficiency and long-term stability. Rational design of the 2D spacer cation is important to achieve a win–win situation for defects' passivation and photogenerated carrier extraction. Herein, we carry out first-principles calculation to analyze the dipole moment of phenethylamine-type molecules and their resulting 2D/3D perovskites. Based on the results of theoretical calculation, the dipole moment of 2D cations can be well tuned by varying the number of fluorine atoms on the para-position of the benzene ring, which further determines the interfacial dipole across the 2D/3D heterojunction interface. A high dipole 2D perovskite layer at the interface between the 3D perovskite and hole-transporting material is found to promote charge transport and suppress charge trapping efficiently. As a result, our 2D/3D PSCs exhibit a champion power conversion efficiency over 22% and a fill factor over 83%. Moreover, our solar cells also show a remarkable stability, maintaining 80% of its initial efficiency for more than 1400 h without encapsulation under a 30 ± 5% relative humidity.