Heteroatom engineering of ortho-fluorinated triarylamine based hole transport materials for enhanced performance in perovskite solar cells

Abstract

The development of cost-effective and high-performance charge transport materials is of paramount importance for advancing the commercialization of perovskite solar cells (PSCs). In this study, we present three cost-effective hole transport materials (HTMs) featuring strategically engineered intramolecular noncovalent interactions, which collectively enhance both the efficiency and stability of PSCs. These HTMs adopt a donor–π–donor (D–π–D) molecular architecture, incorporating a dithieno[3,2-b:2′,3′-d]pyrrole (DTP) core functionalized with various ortho-fluorinated triarylamine donor units. Through systematic modification of the terminal groups, we designed three distinct HTMs: DTP-FO, bearing terminal methoxy substituents [4,4′-(4-(4-methoxyphenyl)-4H-dithieno[3,2-b:2′,3′-d]pyrrole-2,6-diyl)bis(3-fluoro-N,N-bis(4-methoxyphenyl)aniline)]; DTP-FS, featuring terminal methylthio substituents [4,4′-(4-(4-methoxyphenyl)-4H-dithieno[3,2-b:2′,3′-d]pyrrole-2,6-diyl)bis(3-fluoro-N,N-bis(4-(methylthio)phenyl)aniline)]; and DTP-FOS, a hybrid structure incorporating both methoxy and methylthio substituents [4,4′-(4-(4-methoxyphenyl)-4H-dithieno[3,2-b:2′,3′-d]pyrrole-2,6-diyl)bis(3-fluoro-N-(4-methoxyphenyl)-N-(4-(methylthio)phenyl)aniline)]. These tailored structural modifications induce intramolecular noncovalent interactions that effectively regulate the optoelectronic properties, film structures, and charge transport characteristics of the HTMs. PSCs fabricated with DTP-FO, DTP-FS, and DTP-FOS achieved average power conversion efficiencies (PCEs) of 20.5%, 22.5%, and 23.6%, respectively. Remarkably, the DTP-FOS-based device retained 75% of its initial efficiency after 2500 hours of continuous illumination under maximum power point tracking at 25 °C. Furthermore, both DTP-FS and DTP-FOS outperformed the benchmark 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD) (PCE of 21.4%) not only in terms of PCE, but also in thermal and photostability, indicating their considerable potential for realizing stable and scalable PSC technologies.