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Effect of Molecule-Surface Reaction Mechanism on the Electronic Characteristics and Photovoltaic Performance of Molecularly Modified Si.

Yaffe O, Ely T, Har-Lavan R, Egger DA, Johnston S, Cohen H, Kronik L, Vilan A, Cahen D - J Phys Chem C Nanomater Interfaces (2013)

Bottom Line: However, the surface-insensitive RCR reaction leads to more dense monolayers and, therefore, to much better chemical stability, with lasting protection of the Si surface against oxidation.This is reflected in longer minority carrier lifetimes, lower reverse currents in the dark, and improved photovoltaic performance, over what is obtained if only one of the mechanisms operates.It further suggests an approach for effective passivation of other semiconductors.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials & Interfaces, Weizmann Institute of Science , Rehovoth 76100, Israel.

ABSTRACT
We report on the passivation properties of molecularly modified, oxide-free Si(111) surfaces. The reaction of 1-alcohol with the H-passivated Si(111) surface can follow two possible paths, nucleophilic substitution (SN) and radical chain reaction (RCR), depending on adsorption conditions. Moderate heating leads to the SN reaction, whereas with UV irradiation RCR dominates, with SN as a secondary path. We show that the site-sensitive SN reaction leads to better electrical passivation, as indicated by smaller surface band bending and a longer lifetime of minority carriers. However, the surface-insensitive RCR reaction leads to more dense monolayers and, therefore, to much better chemical stability, with lasting protection of the Si surface against oxidation. Thus, our study reveals an inherent dissonance between electrical and chemical passivation. Alkoxy monolayers, formed under UV irradiation, benefit, though, from both chemical and electronic passivation because under these conditions both SN and RCR occur. This is reflected in longer minority carrier lifetimes, lower reverse currents in the dark, and improved photovoltaic performance, over what is obtained if only one of the mechanisms operates. These results show how chemical kinetics and reaction paths impact electronic properties at the device level. It further suggests an approach for effective passivation of other semiconductors.

No MeSH data available.


Related in: MedlinePlus

Simplified schemes of the different reaction mechanisms on Si(111)and resulting monolayer structures. (a) Reaction of 1-aloxide (conjugatedbase of 1-alcohol21) via SN mechanism,as a result of moderate heating to 80 °C. (b) Reaction of 1-alcoholvia RCR mechanism, initiated by UV irradiation. (c) Reaction of 1-alkenevia RCR mechanism initiated by high thermal activation (200 °C).R = C8H16CH3; R′ = C9H18CH3.
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fig1: Simplified schemes of the different reaction mechanisms on Si(111)and resulting monolayer structures. (a) Reaction of 1-aloxide (conjugatedbase of 1-alcohol21) via SN mechanism,as a result of moderate heating to 80 °C. (b) Reaction of 1-alcoholvia RCR mechanism, initiated by UV irradiation. (c) Reaction of 1-alkenevia RCR mechanism initiated by high thermal activation (200 °C).R = C8H16CH3; R′ = C9H18CH3.

Mentions: nucleophilic substitution(SN) of an alkoxide (conjugated base of the alcohol) thatproceeds (for the ideal Si(111) surface) through a pentavalent siliconcomplex as an intermediate species21,26 (Figure 1a);


Effect of Molecule-Surface Reaction Mechanism on the Electronic Characteristics and Photovoltaic Performance of Molecularly Modified Si.

Yaffe O, Ely T, Har-Lavan R, Egger DA, Johnston S, Cohen H, Kronik L, Vilan A, Cahen D - J Phys Chem C Nanomater Interfaces (2013)

Simplified schemes of the different reaction mechanisms on Si(111)and resulting monolayer structures. (a) Reaction of 1-aloxide (conjugatedbase of 1-alcohol21) via SN mechanism,as a result of moderate heating to 80 °C. (b) Reaction of 1-alcoholvia RCR mechanism, initiated by UV irradiation. (c) Reaction of 1-alkenevia RCR mechanism initiated by high thermal activation (200 °C).R = C8H16CH3; R′ = C9H18CH3.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3814651&req=5

fig1: Simplified schemes of the different reaction mechanisms on Si(111)and resulting monolayer structures. (a) Reaction of 1-aloxide (conjugatedbase of 1-alcohol21) via SN mechanism,as a result of moderate heating to 80 °C. (b) Reaction of 1-alcoholvia RCR mechanism, initiated by UV irradiation. (c) Reaction of 1-alkenevia RCR mechanism initiated by high thermal activation (200 °C).R = C8H16CH3; R′ = C9H18CH3.
Mentions: nucleophilic substitution(SN) of an alkoxide (conjugated base of the alcohol) thatproceeds (for the ideal Si(111) surface) through a pentavalent siliconcomplex as an intermediate species21,26 (Figure 1a);

Bottom Line: However, the surface-insensitive RCR reaction leads to more dense monolayers and, therefore, to much better chemical stability, with lasting protection of the Si surface against oxidation.This is reflected in longer minority carrier lifetimes, lower reverse currents in the dark, and improved photovoltaic performance, over what is obtained if only one of the mechanisms operates.It further suggests an approach for effective passivation of other semiconductors.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials & Interfaces, Weizmann Institute of Science , Rehovoth 76100, Israel.

ABSTRACT
We report on the passivation properties of molecularly modified, oxide-free Si(111) surfaces. The reaction of 1-alcohol with the H-passivated Si(111) surface can follow two possible paths, nucleophilic substitution (SN) and radical chain reaction (RCR), depending on adsorption conditions. Moderate heating leads to the SN reaction, whereas with UV irradiation RCR dominates, with SN as a secondary path. We show that the site-sensitive SN reaction leads to better electrical passivation, as indicated by smaller surface band bending and a longer lifetime of minority carriers. However, the surface-insensitive RCR reaction leads to more dense monolayers and, therefore, to much better chemical stability, with lasting protection of the Si surface against oxidation. Thus, our study reveals an inherent dissonance between electrical and chemical passivation. Alkoxy monolayers, formed under UV irradiation, benefit, though, from both chemical and electronic passivation because under these conditions both SN and RCR occur. This is reflected in longer minority carrier lifetimes, lower reverse currents in the dark, and improved photovoltaic performance, over what is obtained if only one of the mechanisms operates. These results show how chemical kinetics and reaction paths impact electronic properties at the device level. It further suggests an approach for effective passivation of other semiconductors.

No MeSH data available.


Related in: MedlinePlus