Role of Interfacial Potential Drops on Redox‐Couple Dependent Voltages Using Hybridized Si(111)–(Bis)Anthracene Photoelectrodes

Abstract

Abstract We investigate the flat band voltage (VFB) of silicon (Si) surfaces functionalized with methyl (Me), 9‐anthracene (Anth), 1,8‐anthracene (DiAnth; two attachment points), and 9‐bianthracene (BiAnth) on n‐type and p‐type Si substrates. Flat band potential (EFB, by Mott‐Schottky) provided VFB (or VBI) dependent on the contacted redox couple (ERedox). On p‐type Si, VFB increased linearly until a limiting value was reached; similarly, the n‐type Si VFB decreased linearly until it plateaued at more negative potentials. Notably, the slope of VFB depended on the surface modifier, exhibiting opposite trends for p‐type and n‐type Si. Curiously, anthracene‐functionalized p‐Si exhibited an unexpectedly more shallow (and beneficial) slope than ‐methyl, attributed to the polarizability of the anthracene π electron cloud and a potential drop across the molecular interface. On n‐type Si, anthracene‐functionalized surfaces displayed a higher slope than ‐methyl, suggesting a gradual cancellation of the voltage shift effect due to a fixed surface dipole. We also quantified the interfacial potential drop across p‐Si–Anth as 275 mV using variable frequency (10 kHz vs 1 kHz) Mott‐Schottky analysis. The interfacial potential drop and dipoles that result from molecular functionalization are thus critical design parameters for PEC cells that utilize moderate‐potential redox couples or reactions; however, such effects are negligible with redox couples that reside at or beyond the semiconductor band‐edge.

Keywords

• Surface dipoles
• Band bending
• Potential drop
• Semiconductor-liquid interface