Semiconductor Spacer with Donor-Acceptor Structure Drives 2D Ruddlesden–Popper Perovskite Solar Cells Beyond 20% Efficiency

Two dimensional (2D) Ruddlesden–Popper (RP) perovskites have emerged as promising photovoltaic materials. However, their further improvement in photovoltaic efficiency is hindered by the large dielectric mismatch and high exciton binding energy caused by the insulating spacers. Herein, two semiconductor spacers, namely MeBThMA and CNBThMA, were developed for 2D RP perovskite solar cells (PSCs). In contrast to MeBThMA, the CNBThMA spacer, which features a donor-acceptor (D-A) structure, exhibits a larger dipole moment and adopts a face-to-face molecular stacking arrangement in the single crystal. The unique D-A structure effectively eliminates the dielectric mismatch between the organic and inorganic layers, contributing the formation of energy levels, adjusting the anisotropic charge transport properties, and improving the film quality of layered RP perovskites. Consequently, the devices based on CNBThMA (nominal n = 5) achieved a champion efficiency of 20.82%, which is a record efficiency for 2D RP PSCs using semiconductor spacers to the best of our knowledge. Our work pioneers a novel way to design organic semiconductor spacers using a D-A structure for highly efficient 2D PSCs.