"T-shaped" Carbazole Alkylammonium Cation Passivation in Perovskite Solar Cells

Incorporating alkylammonium cations atop the 3D perovskite enables effective defect passivation and significantly enhances the power conversion efficiency of perovskite solar cells. However, the diversity and durability of this passivation strategy have been limited to the ligand type and diffusion of ligands due to high reactivity. Here, we designed bulky "T-shaped" conjugated carbazole alkylammonium cations with inner pi-pi interaction and enlarged steric hindrance to minimize ligand diffusion while maintaining passivation effects. As verified by grazing incidence X-ray diffraction and transient absorption spectra, these "T-shaped" passivators could keep a stable intrinsic crystal phase on the perovskite surface after thermal aging. Additionally, the devices utilizing these organic semiconductor-based "T-shaped" ligands were relatively constant in series resistance and introduced higher hole mobility than the PEAI. Finally, the champion device using the "T-shaped" passivator achieved a maximum device efficiency of 25.1% with improved operational stability under 1 sun illumination.