This study investigated the use of co-adsorbed self-assembled monolayers (CA-SAMs) to enhance interfacial properties and charge extraction in perovskite photoelectronic devices. Through sequential adsorption of MeO-2PACz and 3PATAT-C3, CA-SAMs formed a uniform and favorable dipole layer on ITO substrates, enabling improved energy-level alignment and molecular coverage. This interfacial design facilitated better perovskite crystallization with enlarged grains and enhanced film quality, leading to suppressed trap-assisted recombination. Photoluminescence analysis showed prolonged carrier lifetime, while electrical measurements revealed over an order of magnitude reduction in dark current, along with higher detectivity and signal-to-noise ratio. Devices with CA-SAMs also exhibited improved operational stability. These results demonstrate that CA-SAMs serve as an effective interfacial design for improving performance and durability in perovskite-based optoelectronic systems.