Origin of charged gap states in<i>a</i>-Si:H and their evolution during light soaking

Nádaždy, Vojtěch; Zeman, Miro

doi:10.1103/physrevb.69.165213

Cited by 35 publications

(21 citation statements)

References 32 publications

(39 reference statements)

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“…2(b)) of both defect states before the dangling bond creation near midgap and a simultaneous increase in the capture coefficients of the shallower states [2]. A similar decay of the DOS was also reported recently by deep level transient spectroscopy experiments [4].…”

Section: Resultsmentioning

confidence: 51%

“…This assignment is supported from the fact that both centers could be removed upon LS as recently suggested in Refs. [2] and [4], which can explain the unusual decay of the DOS above midgap (Fig. 2(b)).…”

Section: Discussionmentioning

confidence: 91%

“…On the other hand, the defects with the highest capture coefficients can be attributed, in general, to dangling bonds with a Si-H bond next to them in order to explain their high capture probability [1]. The hydrogen three-bond center, SiHSi [2], and an over-coordinated defect complex [4], "SiH þ 2 , are good candidates for the two defects with the higher capture coefficients c H n and c I n . This assignment is supported from the fact that both centers could be removed upon LS as recently suggested in Refs.…”

Section: Discussionmentioning

confidence: 99%

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The nature of the defect states above midgap and their role in the light-induced metastability of a-Si:H

Kounavis

2006

Journal of Non-Crystalline Solids

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Section: Resultsmentioning

confidence: 51%

Section: Discussionmentioning

confidence: 91%

Section: Discussionmentioning

confidence: 99%

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The nature of the defect states above midgap and their role in the light-induced metastability of a-Si:H

Kounavis

2006

Journal of Non-Crystalline Solids

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“…Another interesting point on the V oc increase in the literature is that none of those studies addressed comprehensive study with kinetics of J sc . It has also been reported that aSi:H shows very fast creation of charged gap states during light-soaking which could be related to the fast degradation kinetics of the pm-Si:H cell [23], but midgap state creation should lead to a decrease in V oc in addition to that of the overall efficiency. Therefore, we consider that fast state creation is insufficient for the explanation behind the particular degradation of pm-Si:H solar cells and that other phenomena must be involved.…”

Section: Evolution Of the Solar Cell Parameters As A Functionmentioning

confidence: 99%

Light induced electrical and macroscopic changes in hydrogenated polymorphous silicon solar cells

et al. 2012

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We report on light-induced electrical and macroscopic changes in hydrogenated polymorphous silicon (pm-Si:H) PIN solar cells. To explain the particular light-soaking behavior of such cells -namely an increase of the open circuit voltage (Voc) and a rapid drop of the short circuit current density (Jsc) -we correlate these effects to changes in hydrogen incorporation and structural properties in the layers of the cells. Numerous techniques such as current-voltage characteristics, infrared spectroscopy, hydrogen exodiffusion, Raman spectroscopy, atomic force microscopy, scanning electron microscopy and spectroscopic ellipsometry are used to study the light-induced changes from microscopic to macroscopic scales (up to tens of microns). Such comprehensive use of complementary techniques lead us to suggest that light-soaking produces the diffusion of molecular hydrogen, hydrogen accumulation at p-layer/substrate interface and localized delamination of the interface. Based on these results we propose that light-induced degradation of PIN solar cells has to be addressed from not only as a material issue, but also a device point of view. In particular we bring experimental evidence that localized delamination at the interface between the p-layer and SnO2 substrate by light-induced hydrogen motion causes the rapid drop of Jsc.

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“…Instead, the breaking of weak Si-Si bonds due to nonradiative recombination of electron-hole pairs is considered today as a plausible origin for the Staebler-Wronski effect. 16,17 Recently, Powell et al 17 proposed the creation of two metastable HSiDB ͓complex of a DB and a Si-H bond, where H locates in a tetrahedral-like site ͑T d ͒, not a bond-centered site͔ defects; a H atom from a neighboring doubly hydrogenated weak Si-Si bond ͑HSiSiH͒ switches to a T d site of the broken Si-Si bond and the other H from HSiSiH is also located in the energetically suitable T d site. This model is acceptable because the spatial separation between H in the T d site and DB is in agreement with the observed values of 4 -5 Å by electron spin resonance ͑ESR͒ measurements.…”

mentioning

confidence: 99%

Modeling of annealing kinetics for hydrogenated-amorphous-silicon-based solar cells using two-component metastable defects

Myong

Lim

2006

Applied Physics Letters

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We propose a kinetic model for the annealing in p-i-n-type hydrogenated-amorphous-silicon ͑a-Si: H͒-based solar cells using a combination of the fill factor and "fast" and "slow" metastable defect states in their absorbers. Reported annealing data are simulated on p-i-n-type a-Si: H-based solar cells using the proposed model in order to confirm its validity. The recovery kinetic dependence on the thermal annealing temperature, biased voltage, and phase of the absorber controlled by the hydrogen dilution ratio during deposition are reviewed. Furthermore, we suggest a recovery mechanism for the solar cells based on long range hydrogen diffusion. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2213507͔Despite high interest of late in thin-film Si solar modules, a major obstacle to their commercialization remains. Specifically, light-induced degradation, which originates from the photocreation of dangling bonds ͑DBs͒ accomplished by the nonradiative recombination of photogenerated electron-hole pairs ͑Staebler-Wronski effect͒, 1 limits the efficiency of hydrogenated-amorphous-silicon ͑a-Si: H͒-based solar cells. In spite of extensive research on the StaeblerWronski effect during the past 30 years, there is no consensus on a microscopic mechanism that explains all experimental phenomena. Similarly, the recovery mechanism for a-Si: H-based solar cells through thermal annealing 2,3 or intense illumination at high temperature with a strong reverse bias 4 has yet to be identified: the recovery kinetics against thermal annealing is often interpreted by the stretched exponential kinetics 5,6 wherein defect generation and annealing for a-Si: H-based materials are controlled by only one type of metastable defect as a result of a dispersive process. 7 However, several recent studies have provided experimental evidence that a-Si: H-based materials possess "fast" and "slow" metastable defects, which is clearly contradictory to the stretched exponential kinetic model. [8][9][10] Thus, the stretched exponential kinetic model is no longer considered appropriate and the total defect density cannot uniquely determine the state for the a-Si: H-based solar cells. In the present work, a model of recovery kinetics for p-i-n-type a-Si: H-based solar cells employing the two-component metastable defect states is suggested.The fill factor ͑FF͒ was selected as a measure of the state for the a-Si: H-based solar cells due to the following reasons. ͑i͒ FF is sensitive to the quality of the intrinsic ͑i͒ absorber. ͑ii͒ Analytic equations relating FF to the collection length, i.e., FFϰ E, where and are the average mobility and lifetime of photogenerated carriers and E is the internal electric field in the i absorber, and to the defect density ͑or electron spin density͒ have been developed. 11 ͑iii͒ FF is the most degraded parameter against light soaking in a-Si: H-based solar cells 6,12 and is less sensitive to the measurement temperature and illumination intensity compared to the opencircuit voltage and short-circuit current. 2 FF for p-i-...

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Origin of charged gap states ina-Si:H and their evolution during light soaking

Cited by 35 publications

References 32 publications

The nature of the defect states above midgap and their role in the light-induced metastability of a-Si:H

The nature of the defect states above midgap and their role in the light-induced metastability of a-Si:H

Light induced electrical and macroscopic changes in hydrogenated polymorphous silicon solar cells

Modeling of annealing kinetics for hydrogenated-amorphous-silicon-based solar cells using two-component metastable defects

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