Inverted perovskite solar cells (PSCs) with a planar p–i–n architecture are promising for high-efficiency PSCs [1]. However, their conventional metal cathode limits their stability and flexibility for practical device applications. Single-walled carbon nanotubes (SWCNTs) exhibit high conductivity, flexibility, and tunable electronic properties, making them an appealing option for next-generation electrodes. However, their inherent p-type character and unfavourable work function relative to the perovskite conduction band constrain their use as cathodes in PSCs [2]. We demonstrated that organophosphorus molecular dopants could convert intrinsically p-type FCCVD-grown single-walled carbon nanotube (SWCNT) films into stable n-type cathodes, enabling efficient inverted PSCs with doped SWCNT/PCBM electrodes [3]. Nevertheless, organophosphorus dopants often suffer from relatively weak interfacial contact with the SWCNT network, limited π–π interactions due to their non-planar σ-bonding frameworks, and potential dedoping or degradation under prolonged operation. Building on this molecular n-type doping concept, we therefore explored a molecular design strategy based on planar aromatic dopants to clarify their role in SWCNT doping and their effect on device performance.

Here, we employ three π-conjugated n-type dopants, two perylene diimide derivatives (PDIN and PDINBr₂) and one naphthalene diimide derivative (NDIN), to modulate the electronic properties of SWCNT films and optimize their energy-level alignment with the perovskite absorber and PCBM interlayer. Near-infrared absorption, Raman spectroscopy, and Seebeck measurements confirm a clear p- to n-type conversion for all dopants, accompanied by an increase in electron carrier concentration. Photoelectron yield spectroscopy reveals a substantial change in the SWCNT work function, bringing it closer to the PCBM LUMO level. Density functional theory calculations further reveal strong interfacial charge transfer and favorable frontier orbital alignment, with the planar perylene core and electron-withdrawing bromine substituents in PDINBr₂ providing the most pronounced doping effect. When implemented as cathodes in inverted PSCs (glass/ITO/PEDOT:PSS /MAPbI₃/PC₆₀BM/n-doped SWCNT), doped SWCNT electrodes exhibit significantly improved photovoltaic performance compared with undoped SWCNT devices. The champion device based on PDINBr₂-doped SWCNT achieves a power conversion efficiency (PCE) of 10.12%. Microwave photoconductivity decay analyses indicate that the optimized planar aromatic dopants reduce interfacial recombination and enhance electron extraction at the perovskite/PCBM/SWCNT junction. This work demonstrates a novel strategy for utilizing planar aromatic molecular dopants to enable SWCNTs as cathodes, paving the way for versatile, high-performance carbon nanotube–based electrodes in next-generation perovskite photovoltaics. Part of these findings has been published in EES Solar, Royal Society of Chemistry [4].