Molecular engineering of arylamine-based organic hole-transport materials for efficient perovskite solar cells

The development of high-performance hole-transport materials (HTMs) with excellent stability for perovskite solar cells (PSCs) is in great demand for pushing their large-scale applications. Herein, we report the synthesis of aromatic triamine-based HTMs, specifically 6-(4-((4-(6-(bis(4-methoxyphenyl)amino)naphthalen-2-yl)phenyl)(4-methoxyphenyl)amino)phenyl)-N,N-bis(4-methoxyphenyl)naphthalen-2-amine (XL6), 6-(4-((4-(6-(bis(4-methoxyphenyl)amino)naphthalen-2-yl)phenyl)(phenyl)amino)phenyl)-N,N-bis(4-methoxyphenyl)naphthalen-2-amine (XL7), and 6-(4-((4-(6-(diphenylamino)naphthalen-2-yl)phenyl)(phenyl)amino)phenyl)-N,N-diphenylnaphthalen-2-amine (XL8). These compounds are synthesized with ease and exhibit high solubility in organic solvents, yielding analytically pure materials. Notably, XL8 demonstrates a high glass-transition temperature of 140°C and a hole mobility in the range of (1.27-5.54) × 10^-3 cm² V^-1 s^-1 under an electric field of (1-4) × 10⁵ V cm^-1. The absence of electron-donating methoxy groups in XL8 results in a lower highest occupied molecular orbital (HOMO) level of -5.36 eV, which contributes to its highly efficient charge extraction from photoexcited perovskites. Consequently, inverted PSCs incorporating XL8 as the HTM achieve a power conversion efficiency (PCE) of 21.74%, with an open-circuit voltage (V_OC) of 1.09 V, a short-circuit current density (J_SC) of 24.80 mA cm^-2, and a fill factor (FF) of 80.19%. This performance surpasses that of devices based on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), which exhibit a PCE of 17.87%, V_O of 1.05 V, J_SC of 23.2 mA cm^-2, and FF of 73.37%.