T-shaped-n-doped polycyclic aromatic hydrocarbons: a new concept of dopant-free organic hole-transporting materials for perovskite solar cells

Although metal halide perovskites are positioned as the most powerful light-harvesting materials for sustainable energy conversion, there is a need for a thorough understanding of molecular design principles that would guide better engineering of organic hole-transporting materials, which are vital for boosting the performance and stability of perovskite solar cells. To address this formidable challenge, here, we developed a new design strategy based on the curved N-doped polycyclic aromatic hydrocarbon merged with T-shaped phenazines being decorated with (phenyl)-di-p-methoxyphenylamine (OMeTAD)-N-PAH23/24 and -3,6-ditertbutyl carbazole (TBCz)-N-PAH25/26. As N-PAH23/24 exhibited satisfying thermal stability, the comparative studies performed with various experimental and simulation methods revealed a pronounced correlation between the depth of the central cyclazine core and the form of the T-shape units. This proved to be a crucial factor in controlling their pi-pi intermolecular interaction as well as self-assembly behavior with the perovskite layer, leading to enhanced humidity resistance, operational stability, and a maximum power conversion efficiency of 20.39% denoted for N-PAH23, which is superior to the benchmarked device with doped spiro-OMeTAD (19.23%). These studies not only resulted in optimized stability and device performance but also opened a conceptually new chemical space in the photovoltaic technology.