Highly efficient and stable planar CsPbI2Br perovskite solar cell with a new sensitive-dopant-free hole transport layer obtained via an effective surface passivation

Hole transport layers (HTLs) plays critical role in CsPbI2Br perovskite solar cells (PSCs). However, few studies have been done to develop new and sensitive-dopant-free HTL for CsPbI2Br PSCs. Here, a low-cost fluorinated N',N',N'',N''-tetrakis(4-methoxyphenyl)spiro[fluorene-9,9'-xanthene]-2,7-diamine (2mF-X59) was synthesized and applied as sensitive-dopant-free HTL into CsPbI2Br PSCs. After modified the 2mF-X59 and CsPbI2Br surface by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquino-dimethane (F4-TCNQ), a maximum power conversion efficiency (PCE) of 14.42% was obtained for CsPbI2Br PSC with an impressive open-circuit voltage (Voc) of 1.23 V, which is higher than that of the most previously reported CsPbI2Br PSCs with the doped Spiro-OMeTAD. More importantly, the CsPbI2Br PSCs with the newly developed HTLs showed remarkable stability retaining more than 94% of their initial PCE value after aging in air for 30 days without encapsulation. Therefore, we firmly believe that our new 2mF-X59 HTL created via molecular engineering is a promising candidate for preparing high performance CsPbI2Br PSCs. A new sensitive-dopant-free HTL (2mF-X59) was synthesized and successfully applied in a planar CsPbI2Br PSC. A power conversion efficiency (PCE) of 14.42% was obtained in the CsPbI2Br PSC with 2mF-X59 + F4-TCNQ as HTL by interface engineering. The unencapsulated device displayed remarkable stability, retaining above 94% of its initial PCE after storing in ambient atmosphere for 30 days. [Display omitted] •2mF-X59 was firstly synthesized to instead of spiro-OMeTAD in CsPbI2Br perovskite solar cells. As we know, few works have been report about using new HTL in inorganic perovskite solar cell.•F4-TCNQ was used as additive for 2mF-X59 hole transport layer (HTL), A High efficiency of 13.42% was obtained in CsPbI2Br solar cell with 2mF-X59 + F4TCNQ HTL, which is comparable to device with spiro-OMeTAD + Li-TFSI + t-BP as HTL (PCE = 13.75%).•In order to further improve the efficiency of CsPbI2Br solar cell, F4-TCNQ was used to passivate the surface of CsPbI2Br film. The efficiency of CsPbI2Br solar cell with 2mF-X59 + F4TCNQ HTL was further improved from 13.42 to 14.42%.