Microscopic Description of Light Induced Defects in Amorphous Silicon Solar Cells

Wagner, Lucas K.; Grossman, Jeffrey C.

doi:10.1103/physrevlett.101.265501

Cited by 40 publications

(43 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Overall, we learn from this that for compressive strains delocalization is important and for tensile strains the db-character is enhanced. Most notably, the latter finding illustrates that spin localizes much more strongly due to a dangling bond in comparison to regions of strain, which yield rather delocalized spin distributions 19,38 .…”

Section: Strainmentioning

confidence: 88%

Dangling-bond defect in a-Si:H: Characterization of network and strain effects by first-principles calculation of the EPR parameters

et al. 2013

View full text Add to dashboard Cite

The performance of hydrogenated amorphous silicon (a-Si:H) solar cells is severely affected by the light-induced formation of metastable defects in the material (Staebler-Wronski effect). The common notion is that the dangling-bond (db) defect, a three-fold coordinated silicon atom, plays a key role in the underlying mechanisms. To support the characterization of this defect by electron paramagnetic resonance (EPR), we present in this work a first-principles study of the EPR-parameters for a structural ensemble of the db-defect. We show that the a-Si:H dangling bond is a network defect, for which charge and spin localization substantially depend on the actual coordination of the db-atom and the local geometric and electronic structure of the immediate surrounding. It consequently differs by its very nature from its crystalline counterpart, which is typically related to the presence of a vacancy. The application of hydrostatic strain to our models yields further insights into the dependence of the hyperfine interaction on the structural characteristics of the defect. The observed trends are shown to result from the interplay between delocalization and sp-hybridization.

show abstract

Section: Strainmentioning

confidence: 88%

Dangling-bond defect in a-Si:H: Characterization of network and strain effects by first-principles calculation of the EPR parameters

et al. 2013

View full text Add to dashboard Cite

show abstract

“…The gas phase ionization potentials of small molecules, arguably related to the energies of localized holes in solids, are however accurately predicted by even the semi-local functionals that we have considered. Our study may contribute to the understanding of possible mechanisms of deep-hole trap states [9] commonly observed in organic electronics, and may potentially be applicable to covalently bonded solids [6,7,[11][12][13].…”

mentioning

confidence: 99%

Hole Localization in Molecular Crystals from Hybrid Density Functional Theory

2011

View full text Add to dashboard Cite

We use first-principles computational methods to examine hole trapping in organic molecular crystals. We present a computational scheme based on the tuning of the fraction of exact exchange in hybrid density functional theory to eliminate the many-electron self-interaction error. With small organic molecules, we show that this scheme gives accurate descriptions of ionization and dimer dissociation. We demonstrate that the excess hole in perfect molecular crystals form self-trapped molecular polarons. The predicted absolute ionization potentials of both localized and delocalized holes are consistent with experimental values.Charge localization in organic solids and interfaces has important implications for the functioning of organic devices [1, 2]. It has been long suggested that charge carriers in organic molecular crystals may self-trap to form localized small polarons [1][2][3][4] through interaction with the surrounding electron and lattice. Models based on the concept of polaron have led to theoretical understanding of charge transport of these materials (see e.g. [1,5]). On the other hand, direct evidence and atomic scale probe of localized charge states in organic crystals remain lacking. Ab initio computations have recently been summoned to provide accurate quantitative description of polaron state in covalent solids [6,7]. In this work, we apply hybrid density functional theory (DFT) with carefully calibrated admixtures of exact exchange to molecular crystals and conclusively demonstrate from first principles the existence of self-trapped hole polaron in defect-free molecular crystals. Our choice to work with small organic molecules permits systematic analysis of DFT exchange correlation (xc) functionals in both gas and solid phases. It also allows predictions of the absolute ionization potentials (IP) of both polaronic localized and free delocalized hole state in solids, revealing large errors in semilocal (sl) DFT functionals that to our knowledge have never been discussed in the literature. This successfully treatment of hole localization and delocalization properties will aid the understanding of charge trapping [8,9] and carrier mobility [10] that are important for organic electronics.A key prerequisite to such studies is the correct choice of DFT functionals. Previous theoretical studies reveal an extreme sensitivity of charge localization to theoretical approximations [6,7,[11][12][13][14]. Standard semilocal functionals for the xc energy, such as the local density approximation (LDA) and generalized gradient approximation (GGA), have been successful in predicting atomic structures and electronic properties of many molecular complexes and solid state materials. But they tend to fail in systems involving fractional charges, e.g. they dissociate molecular ion H + 2 into 2 H 0.5+ rather than into H + and H. The problem stems from self-interaction error (SIE) in the standard density functionals [15]. For a one electron system SIE is conveniently described as the incomplete cancellation of spurious sel...

show abstract

“…at the place where the bond is missing). We also found regions of strained bonds, which have a very characteristic shape of the associated electronic cloud [27,28]: cylindrical-like clouds crossing Si-Si bonds. Finally, H bridges had the same structure as those observed at the c-Si(100)/a-Si:H interface: a H atom connecting two Si atoms.…”

Section: H Bridge Dangling Bond Strained Bondmentioning

confidence: 76%

Atomistic study of the structural and electronic properties of a-Si:H/c-Si interfaces

Santos

Cazzaniga

Onida

et al. 2014

J. Phys.: Condens. Matter

View full text Add to dashboard Cite

Abstract. We investigate the structural and electronic properties of the interface between hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) by combining tight-binding molecular dynamics and DFT ab inito electrionic stucture calculations. We focus on the c-Si (100) (1×1)/a-Si:H, c-Si(100)(2×1)/a-Si:H and the c-Si(111)/a-Si:H interfaces due to their technological relevance. The analysis of atomic rearrangements induced at the interface by the interaction between H and Si allowed us to identify the relevant steps that lead to the transformation from cSi(100)(1×1)/a-Si:H to c-Si(100)(2×1)/a-Si:H. The interface electronic structure is found to be characterized by spatially localized mid-gap states. Through them we have identified the relevant atomic structures responsible for the interface defect states, namely: dangling-bonds, H bridges, and strained bonds. Our analysis contributes to a better understanding of the role of such defects in c-Si/a-Si:H interfaces

show abstract

Microscopic Description of Light Induced Defects in Amorphous Silicon Solar Cells

Cited by 40 publications

References 31 publications

Dangling-bond defect in a-Si:H: Characterization of network and strain effects by first-principles calculation of the EPR parameters

Dangling-bond defect in a-Si:H: Characterization of network and strain effects by first-principles calculation of the EPR parameters

Hole Localization in Molecular Crystals from Hybrid Density Functional Theory

Atomistic study of the structural and electronic properties of a-Si:H/c-Si interfaces

Contact Info

Product

Resources

About