The use of illuminated semiconductors to drive chemical reactions is a ubiquitous motif in energy-related chemistry. However, understanding and maximizing the performance of such materials is highly dependent on a plethora of variables involving the electronic and structural features of the surface and interface. Here we utilize covalently modified p-Si(111) photocathodes as a model system to understand the effect of surface dipoles and band-edge surface states on photoelectrochemical performance (HER and MV2+ reduction). A series of aryl and aryl-acene units (phenyl, anthracene, and their derivatives) are used to covalently modify silicon interfaces with atomic precision. The Installation of more negative dipoles (SiC+/R-) maximizes downward band-bending (flat-band potential, E-FB), and increasing the molecular density of states at the band-edge energy increases the barrier height (Φ). Both strategies enhance kinetic device performance (Voc). Complementary studies using ALD-TiO2/Pt, surface photovoltage, impedance spectroscopy further ascertain the roles of surface dipoles and band-edge density of states on semiconductor|liquid junctions.

Enhancing Si(111) photocathode performance with surface dipoles and surface density of states

2019 Fall National Meeting

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