Multifunctional interface modification to enhance the performance of perovskite solar cells

Perovskite solar cells (PSCs) have become a research hotspot in the photovoltaic field due to their advantages such as high power conversion efficiency (PCE), low cost, and solution-processing technology. In p-i-n type PSCs, the polycrystalline perovskite film crystallizes in situ on the surface of the hole transport layer (HTL). Therefore, the properties of the HTL/perovskite interface play a decisive role in both the quality of the perovskite film and the efficiency of hole extraction. In this work, phenethylammonium iodide (PEAI) doped with hydroxyethyl cellulose (HEC) (PEAI:HEC) was used to modify the surface of the HTL, poly[bis(4-phenyl)(4-butylphenyl)amine] (poly-TPD). This interface modification reduced the hydrophobicity of the poly-TPD and improved the film quality of perovskite film. Simultaneously, the hydroxyl in HEC interacted with uncoordinated Pb²⁺ ions in the perovskite, effectively passivating defects in perovskite film. Furthermore, the highest occupied molecular orbital (HOMO) energy level of the HTL shifted from 5.16 to 5.32 eV, achieving better alignment with the HOMO level of the perovskite layer (5.4 eV). PEAI forms π-π stacking interactions with poly-TPD, benefiting the transport of holes, enhancing the short-circuit current density (J_SC) of PSCs. Ultimately, the device PCE was significantly improved from 17.75% to 20.92%. This work provides a convenient and effective strategy for improving the efficiency of perovskite solar cells.