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

The BiVO4-silicon artificial leaf represents an attractive candidate for unbiased photoelectrochemical water splitting device, yet its efficiency remains limited by sluggish charge transport in the BiVO4 photoanode. Here we propose a self-assembled molecular-bridge strategy to establish ordered and fast pathways for efficient charge transport between BiVO4 and NiFeCo layered double hydroxide (NiFeCo-LDH) oxygen evolution cocatalysts. To clarify the role of dipole strength, we compare two self-assembled monolayer layers 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, which drives directional hole extraction and suppresses recombination. Consequently, the optimized BiVO4/4PADCB/NiFeCo-LDH photoanode achieves a photocurrent density of 6.35 mA cm–2 at 1.23 V versus a reversible hydrogen electrode, which is competitive with other reported BiVO4-based systems modified with organic interfacial layers. Furthermore, by integrating the photoanode with a silicon solar cell, a standalone artificial leaf (1.5 cm2 area) is constructed, achieving a solar-to-hydrogen conversion efficiency of 8.75% and stable operation for over 60 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 photoelectrochemical water splitting. Solar artificial leaves promise sustainable hydrogen production, but interfacial charge losses limit their efficiency. Here, the authors report ordered molecular layers that promote charge transport and improve water splitting in bismuth vanadate-silicon artificial leaves.