This study introduces a co-adsorption (CA) strategy using 2-chloro-5-(trifluoromethyl)isonicotinic acid (PyCA-3F) to enhance the performance of perovskite solar cells (PSCs) and organic solar cells (OSCs). The CA approach involves co-depositing PyCA-3F with 2-(9H-carbazol-9-yl)ethylphosphonic acid (2PACz) at the buried interface between 2PACz and the perovskite/organic layers. This method effectively reduces the aggregation of 2PACz, improves surface smoothness, and increases the work function of the modified self-assembled monolayer (SAM) layer, leading to a flattened buried interface with enhanced heterojunction properties for perovskite. The improvements result in increased crystallinity, reduced trap states, and enhanced hole extraction and transfer capabilities, achieving power conversion efficiencies (PCEs) exceeding 25% for PSCs with a p-i-n structure (certified at 24.68%) and PCEs of 19.51% for OSCs using the PM1:PTQ10:m-BTP-PhC6 photoactive system. The CA strategy also enhances operational stability, with encapsulated PSCs and OSCs retaining approximately 90% and 80% of their initial PCEs, respectively, after 1000 hours of maximal power point tracking. The work presents a simple, rational, and effective method to improve the performance of SAM-based devices, achieving efficiency breakthroughs in both PSCs and OSCs with a favorable p-i-n device structure and enhanced operational stability.This study introduces a co-adsorption (CA) strategy using 2-chloro-5-(trifluoromethyl)isonicotinic acid (PyCA-3F) to enhance the performance of perovskite solar cells (PSCs) and organic solar cells (OSCs). The CA approach involves co-depositing PyCA-3F with 2-(9H-carbazol-9-yl)ethylphosphonic acid (2PACz) at the buried interface between 2PACz and the perovskite/organic layers. This method effectively reduces the aggregation of 2PACz, improves surface smoothness, and increases the work function of the modified self-assembled monolayer (SAM) layer, leading to a flattened buried interface with enhanced heterojunction properties for perovskite. The improvements result in increased crystallinity, reduced trap states, and enhanced hole extraction and transfer capabilities, achieving power conversion efficiencies (PCEs) exceeding 25% for PSCs with a p-i-n structure (certified at 24.68%) and PCEs of 19.51% for OSCs using the PM1:PTQ10:m-BTP-PhC6 photoactive system. The CA strategy also enhances operational stability, with encapsulated PSCs and OSCs retaining approximately 90% and 80% of their initial PCEs, respectively, after 1000 hours of maximal power point tracking. The work presents a simple, rational, and effective method to improve the performance of SAM-based devices, achieving efficiency breakthroughs in both PSCs and OSCs with a favorable p-i-n device structure and enhanced operational stability.