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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.


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Current density–voltage behavior of (a) the Si-alkoxy80/Hg and (b) Si-alkoxyUV/Hg junction, before (solidline) and after (dashed line) a 1 h exposure to boiling water.
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fig5: Current density–voltage behavior of (a) the Si-alkoxy80/Hg and (b) Si-alkoxyUV/Hg junction, before (solidline) and after (dashed line) a 1 h exposure to boiling water.

Mentions: Although the XPS data (Figure 4) showedno difference between the three types of monolayers in terms of immediateoxidation, the more important question is the long-term chemical passivation,namely, the degree to which the different monolayers protect the Sisurface against the formation of native SiO2. We used 1h immersion in boiling water, which we assume to accelerate the formationof SiO2,63 and current–voltagemeasurements, known to be very sensitive to minute amounts of oxides.43 Figure 5 presents thecurrent–voltage behavior of the Si-alkoxy80/Hg (Figure 5a) and Si-alkoxyUV/Hg junctions (Figure 5b), before (solid line) and after (dashed line)a 1 h exposure to boiling water. The results for the Si-alkyl/Hg junctionare similar to those of the Si-alkoxyUV (not shown).


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)

Current density–voltage behavior of (a) the Si-alkoxy80/Hg and (b) Si-alkoxyUV/Hg junction, before (solidline) and after (dashed line) a 1 h exposure to boiling water.
© Copyright Policy
Related In: Results  -  Collection

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

fig5: Current density–voltage behavior of (a) the Si-alkoxy80/Hg and (b) Si-alkoxyUV/Hg junction, before (solidline) and after (dashed line) a 1 h exposure to boiling water.
Mentions: Although the XPS data (Figure 4) showedno difference between the three types of monolayers in terms of immediateoxidation, the more important question is the long-term chemical passivation,namely, the degree to which the different monolayers protect the Sisurface against the formation of native SiO2. We used 1h immersion in boiling water, which we assume to accelerate the formationof SiO2,63 and current–voltagemeasurements, known to be very sensitive to minute amounts of oxides.43 Figure 5 presents thecurrent–voltage behavior of the Si-alkoxy80/Hg (Figure 5a) and Si-alkoxyUV/Hg junctions (Figure 5b), before (solid line) and after (dashed line)a 1 h exposure to boiling water. The results for the Si-alkyl/Hg junctionare similar to those of the Si-alkoxyUV (not shown).

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