Extending the π‐Conjugated System in Spiro‐Type Hole Transport Material Enhances the Efficiency and Stability of Perovskite Solar Modules

Abstract Hole transport materials (HTMs) are a key component of perovskite solar cells (PSCs). The small molecular 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenyl)‐amine‐9,9′‐spirobifluorene (spiro‐OMeTAD, termed “Spiro”) is the most successful HTM used in PSCs, but its versatility is imperfect. To improve its performance, we developed a novel spiro‐type HTM (termed “DP”) by substituting four anisole units on Spiro with 4‐methoxybiphenyl moieties. By extending the π‐conjugation of Spiro in this way, the HOMO level of the HTM matches well with the perovskite valence band, enhancing hole mobility and increasing the glass transition temperature. DP‐based PSC achieves high power conversion efficiencies (PCEs) of 25.24 % for small‐area (0.06 cm 2 ) devices and 21.86 % for modules (designated area of 27.56 cm 2 ), along with the certified efficiency of 21.78 % on a designated area of 27.86 cm 2 . The encapsulated DP‐based devices maintain 95.1 % of the initial performance under ISOS‐L‐1 conditions after 2560 hours and 87 % at the ISOS‐L‐3 conditions over 600 hours.