A Bisphosphonic Acid-functionalized Carbazole for Dual Hydrophilic Interfaces Toward Efficient and Stable Organic Solar Cells

Carbazole derivatives with a single phosphonic acid (PA) group are widely used as monolayer interfaces in perovskites and organic solar cells (OSCs). However, their hydrophilic nature renders ITO electrodes hydrophobic, limiting further applications. In this study, a novel carbazole-based compound functionalized with two PA groups, denoted 2PACz-D1, was designed to create a dual hydrophilic interface. This configuration enables the formation of a bilayer hole-transporting layer (HTL). Specifically, one PA group anchors to the ITO electrode, while the other generates a secondary hydrophilic surface. This allows the subsequent deposition of hydrophilic PEDOT:PSS, forming a protective bilayer HTL that shields ITO from corrosive acidic polymers. The OSCs incorporating this bilayer HTL achieved a power conversion efficiency of 19.44% and exhibited improved thermal stability compared to devices with a single HTL. This work demonstrates the potential of bis-PA carbazole derivatives for tailoring the HTL surface properties, offering promising opportunities for various organic electronic devices.