Multifunctional Ruthenium Dye Assists PTAA-Based Inverted Perovskite Solar Cells

In inverted perovskite solar cells (PSCs), although PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) has been extensively utilized as a hole transport material, its inherent poor wettability and energy level misalignment with perovskite have become critical issues, limiting the improvement of power conversion efficiency (PCE) and long-term stability of PSCs. For overcoming these challenges, our study employs a typical multifunctional dye molecule, N719 (ditetrabutylammonium cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato) ruthenium(II)), to modify PTAA. Thanks to the incorporation of hydrophilic functional groups in N719, the wettability of the PTAA/N719 film is improved, which in turn boosts the crystallinity of the perovskite film. Additionally, the rich functional groups in N719 can interact with uncoordinated Pb²⁺, thereby reducing the defect state density in perovskite. Furthermore, the improved energy level alignment enhances hole extraction capability. Ultimately, the champion device fabricated based on the PTAA/N719 film had a PCE as high as 23.83%, showing a significant improvement compared to the PCE of the unmodified device (20.80%). Moreover, the N719-modified devices exhibited superior long-term stability, with the unencapsulated devices maintaining a PCE greater than 81% of the initial value after being stored for 1500 h under ambient conditions at room temperature. This study demonstrates that dyes represent a promising material for enhancing the performance of inverted PSCs.