Solvent Engineering-Induced Dual Effect on Enhanced Spontaneous Polarization and Charge Transport in Ferroelectric P(VDF-TrFE)-Doped Quasi-2D Perovskites

Incorporation of ferroelectric materials into perovskite solar cells (PSCs) has been demonstrated as an effective approach to elevating the device performance. Dipole polarization of the ferroelectric material can be tuned by an external bias, facilitating the charge transport of PSCs. However, fundamental challenges still exist to utilize the ferroelectric effect in PSCs because the external bias leads to ion migration of the perovskites, deteriorating the performance and long-term stability of the devices. In this study, we report an effective method to improve the spontaneous polarization of the ferroelectric polymer incorporated in a quasi-two-dimensional (2D) perovskite without utilizing the external bias. The solvent engineering strategy effectively enhances the ferroelectric phase and crystallinity of the ferroelectric polymer, improving the local electric field and consequently enhancing charge transport. In addition, the solvent strategy offers the formation of a smooth surface as well as a favorable crystal orientation, leading to a reduced defect density in the quasi-2D perovskite films. Attributed to the dual effects, a significant improvement of the power conversion efficiency is achieved from 6.27 to 14.83%, and it is further improved to 16.65% through fine-tuning of the functional layers' thickness. We believe that the method reported offers an avenue for designing the quasi-2D perovskite without the requirement for structural modification of the PSCs.