Structural Control of Semiconductor Surfaces on Atomic and Nanometer Scales for Efficient Solar Energy Conversion

Abstract

Photoelectrochemistry I Solar cells I Small metal particle I Porous silicon I Surface termination bondStructural control of semiconductor surfaces on an atomic scale and that on a nanometer scale are both important for efficient solar energy conversion. The former is important for achieving low surface carrier recombination, high catalytic activity for interfacial reactions, formation of high energy barriers, etc. The latter is important for simultaneous achievement of all these requirements at one surface, which are in general incompatible with each other for homogeneous surfaces. The structural control on both scales can lead to ideal semiconductor electrodes. Some examples are shown for efficient solar cells and solar-to-chemical conversion by use of metal nano-particles, nanoporous Si layers, and introduction of surface-band asymmetry by formation of Si-halogen termination bonds. * Corresponding

Time Domain Impedance Spectroscopy for Probing the Termination of Silicon (100) Surfaces in Aqueous KOH

“…Surface dipoles arising from polar surface bonds cause a substantial surface potential difference at silicon/electrolyte, [18][19][20][21] silicon/silicon-oxide, and silicon/metal interfaces. 46,47 First principle calculations 46 for the silicon/silicon-oxide interface revealed that a complete replacement of Si-H termination by Si-OH increases the interfacial potential by approximately 1 V. Therefore, polarized surface bonds are also expected to play an important role in the present system.…”

“…The flat band potential (E FB ) of silicon in contact with an electrolyte depends on the surface groups present. [18][19][20][21] This has been demonstrated when Si-OH groups are replaced by Sihalogen groups [18][19][20] and for the chemical formation of Si-OCH 3 surface groups. 21 These shifts have been attributed to surface potential changes due to polar surface bonds.…”

“…21 These shifts have been attributed to surface potential changes due to polar surface bonds. [18][19][20][21] A clear correlation between flat band potential and the difference in electronegativity of the atoms constituting the surface groups has been found, 18 suggesting that measurements of E FB can be used to probe the polarity of surface bonds and therefore their chemical nature.…”

“…The flat band potential ( E FB ) of silicon in contact with an electrolyte depends on the surface groups present. − This has been demonstrated when Si−OH groups are replaced by Si−halogen groups 18-20 and for the chemical formation of Si−OCH 3 surface groups . These shifts have been attributed to surface potential changes due to polar surface bonds. − A clear correlation between flat band potential and the difference in electronegativity of the atoms constituting the surface groups has been found, suggesting that measurements of E FB can be used to probe the polarity of surface bonds and therefore their chemical nature.…”

Roles of Charge Polarization and Steric Hindrance in Determining the Chemical Reactivity of Surface Si−H and Si−Si Bonds at H-Terminated Si(100) and -(111)

“…We reported previously , that the flat-band potentials ( U fb ) of HF-etched n-Si(100) and -(111) in concentrated hydrogen halide (HX) solutions shifted largely toward the negative in the order HF, HCl, HBr, and HI, and explained the shifts to be due to changes in surface potential by formation of Si−X bonds through substitution reaction at surface Si−OH bonds. We reported later that Si−H bonds on H−Si(111) were also changed to Si−X in the concentrated HX solutions if an oxidant such as dissolved air, Br 2 , and I 2 was contained, though the Si−H bonds were stable in the absence of the oxidant.…”