Stable and highly efficient perovskite solar cells: Doping hydrophobic fluoride into hole transport material PTAA

Perovskite solar cells (PSCs) have rapidly developed in the past few years, with a record efficiency exceeding 25%. However, the long-term stability of PSCs remains a challenge and limits their practical application. Many high-performance PSCs have an n-i-p device architecture employing 4-tert-butylpyridine (t-BP) and bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI) as bi-dopants for the hole-transporting layer (HTL). However, the hygroscopicity of Li-TFSI and low boiling point of t-BP negatively impact the moisture stability of these PSC devices. Herein, we report the use of the fluorine-containing hydrophobic compound tris(pentafluorophenyl)phosphine (35FP) as a dopant for poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA). With better hydrophobicity and stability than undoped PTAA, a PSC device containing 35FP-doped PTAA demonstrated improved charge transport properties and reduced trap density, leading to a significant enhancement in performance. In addition, the long-term stability of a 35FP-doped PTAA PSC under air exposure without encapsulation was demonstrated, with 80% of the initial device efficiency maintained for 1,000 h. This work provides a new approach for the fabrication of efficient and stable PSCs to explore hydrophobic dopants as a substitute for hydrophilic Li-TFSI/t-BP.