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.