Surface and grain boundary passivation using tetraphenylethylene derivative for high-performance perovskite solar cell

The efficiency of perovskite solar cells is constrained by surface and bulk recombination, along with poor band alignment at the interfaces of the transport layers. In our study, we demonstrate that modifying the surface and grain boundary (GB) of perovskite using tetraphenylethylene-enamine (TPE-en) enhances band alignment at the perovskite-hole transport layer interface and mitigates recombination within the perovskite material. By leveraging the solubility of small organic molecules in orthogonal solvents, we introduce TPE-en onto the perovskite surface akin to anti-solvent methods. Our investigation reveals a significant enhancement in the short circuit current density, fill factor, and open circuit voltage of the surface-modified (SM) perovskite. Specifically, we achieve a total power conversion efficiency of 18.73% (MA_0.9AA_0.1PbI₃). Comparative analyses show TPE-en outperforms other reported TPE derivatives in device performance. Through systematic interface analysis, we observe that TPE-en effectively reduces surface and GB defects by elevating the HOMO levels of the perovskite, introducing an interface dipole at the perovskite-spiro-OMeTAD interface. Optical measurements such as time-resolved photoluminescence, Ultraviolet photoelectron spectroscopy, and X-ray photoelectron spectroscopy were used to investigate the cause of this improvement. A 0.28 eV surface dipole formed provided effective band alignment, resulting in enhanced hole extraction and photovoltaic performance.