Molecular Design of Hole-Collecting Materials for Co-Deposition Processed Perovskite Solar Cells: A Tripodal Triazatruxene Derivative with Carboxylic Acid Groups

High-performance and cost-effective hole-collecting materials (HCMs) are indispensable for commercially viable perovskite solar cells (PSCs). Here, we report an anchorable HCM composed of a triazatruxene core connected with three alkyl carboxylic acid groups ( 3CATAT-C3 ). In contrast to the phosphonic acid-containing tripodal analog ( 3PATAT-C3 ), 3CATAT-C3 molecules can form a hydrophilic monolayer on a transparent conducting oxide surface, which is beneficial for subsequent perovskite film deposition in the traditional layer-by-layer fabrication process. More importantly, the larger diffusion coefficient and higher surface energy make 3CATAT-C3 suitable for the simplified, cost-effective one-step co-deposition process in which 3CATAT-C3 was directly added as part of the perovskite precursor solution. 3CATAT-C3 is predominantly located at the perovskite bottom surface after spin-coating the mixed precursor solution, facilitating charge extraction. Devices with 3CATAT-C3 fabricated by this co-deposition method exhibit superior performance with a champion power conversion efficiency of over 23%. The unencapsulated devices showed good operational stability (retaining 90% of the initial output after 100 h), thermal durability (retaining 95% of the initial value after heating at 105 °C under air), and excellent storage stability (showing no drop in performance over 8000 h). Based on the results of time-of-flight secondary-ion mass spectroscopy (ToF-SIMS) and diffusion order nuclear magnetic resonance spectroscopy (DOSY), we elucidated the effect of anchoring groups on the performance of the tripodal HCMs in PSCs as well as the mechanism of the co-deposition fabrication process. Our findings provide valuable insights for the molecular design of multifunctional hole-collecting materials, further advancing the performance of perovskite solar cells.