Publication date: 5th November 2025
In perovskite solar cells (PSCs), the replacement of bulk hole-collecting materials with monolayer materials has yielded high-performance devices, primarily due to their superior optical transparency [1]. In contrast, monolayer materials for electron-collecting layers remain underexplored and generally exhibit lower power conversion efficiencies (PCEs) compared to established bulk materials like SnO2 [2].
In this study, we synthesized dithieno-4-keto-1,4-dihydrophosphinine[3]-based phosphonium salt bearing a phosphonic acid anchoring group (DTKPP) (Figure 1a). Electrochemical analysis estimated the LUMO level to be −4.18 eV (Figure 1b). This level is deeper than the Conduction Band Minimum (CBM) of the reference lead perovskite (Cs0.05FA0.80MA0.15PbI2.75Br0.25, CBM: −3.99 eV [4]), confirming a favorable energy offset for efficient electron extraction.
This cationic DTKPP molecule was employed as the electron-collecting monolayer in an n-i-p lead PSC device with the structure: ITO/DTKPP/Cs0.05FA0.80MA0.15PbI2.75Br0.25/Spiro-OMeTAD/Au (Figure 1c). The preliminary device showed a PCE of 11.41% (Figure 1d), highlighting the potential of this novel phosphonium monolayer as an efficient and highly transparent electron-collecting material.
This work was partially supported by JST-Mirai (JPMJMI22E2), NEDO (JPNP20015), NEDO-GI (JPNP21016) programs, International Collaborative Research Program of ICR, Kyoto University, Grant-in-Aid for Scientific Research (A) (JP24H00481), Grant-in-Aid for Scientific Research (B) (JP24K01571, JP24K01607), Grant-in-Aid for Transformative Research Areas (A) (JP25H01262), Grant for Overseas Research by the Division of Graduate Studies (DoGS) of Kyoto university, NSERC of Canada, and the Canada Foundation for Innovation (CFI).
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