Steering directional charge migration via ordered self-assembled molecular layers for efficient BiVO4-silicon artificial leaf

The BiVO 4 -silicon artificial leaf represents a promising unbiased photoelectrochemical (PEC) water splitting device, yet its efficiency remains limited by sluggish charge transport in the BiVO 4 photoanode. To overcome these limitations, we propose a self-assembled molecular-bridge strategy to establish ordered and fast pathways for efficient charge transport between BiVO 4 and NiFeCoO x oxygen evolution cocatalysts (OECs). To clarify the role of dipole strength, we compare two self-assembled monolayers (SAMs) with distinct dipole moments: [4-(9H-carbazol-9-yl)ethyl]phosphonic acid (4PACZ ~ 1.83 Debye) and (4-(7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid (4PADCB ~ 2.54 Debye). The larger dipole of 4PADCB generates a stronger interfacial electric field (IEF), which drives directional hole extraction and suppresses recombination. Consequently, the optimized BiVO 4 /4PADCB/NiFeCoO x photoanode achieves a photocurrent density of 6.35 mA cm⁻ 2 at 1.23 V versus a reversible hydrogen electrode (V RHE ), ranking among the best BiVO 4 -based systems modified with organic interfacial layers. Furthermore, by integrating the photoanode with a silicon solar cell, a standalone artificial leaf (1.5 cm 2 area) was constructed, achieving a solar-to-hydrogen conversion efficiency of 8.75% and stable operation for over 15 hours. This work establishes a clear link between molecular dipole strength and interfacial charge separation, providing a generalizable design principle for molecular interface engineering in PEC water splitting.