Dipole engineering in self-assembled monolayers for efficient organic–silicon hybrid solar cells

Organic–silicon hybrid solar cells, as dopant-free heterojunction devices, hold significant potential for achieving high performance-to-cost ratios in photovoltaics. Critical to their advancement is the engineering of carrier-selective contacts that minimize interfacial losses. Here, we demonstrate a carbazole-based self-assembled monolayer (SAM), [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), as an efficient electron-selective layer in [poly(3,4 ethylenedi oxythiophene):polystyrene sulfonate (PEDOT:PSS)]/Si solar cells. The Me-4PACz SAM introduces a directional dipole moment at the c-Si/Al interface, generating a built-in electric field that enhances electron extraction. This interface modification leads to a linear Ohmic contact, reducing the contact resistivity between n-Si and the metal electrode interface to 4.12 mΩ cm2. Consequently, the optimized device achieves a power conversion efficiency (PCE) of 16.75% with a high open-circuit voltage (VOC) of 651 mV and fill factor of 78.03%, representing a ∼14% relative PCE improvement over the control device (PCE = 14.75%). Our work provides a molecular-scale strategy for tailoring carrier dynamics in silicon-based heterojunctions, offering a pathway toward low-cost, high-efficiency photovoltaic technologies.