Low-temperature a-Si:H/ZnO/Al back contacts for high-efficiency silicon solar cells

Rostan, P.J.; Rau, Uwe; Nguyen, V.X.; Kirchartz, Thomas; Schubert, M.B.; Werner, Jürgen

doi:10.1016/j.solmat.2005.11.010

Cited by 64 publications

(39 citation statements)

References 10 publications

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“…The process parameters, given in Table I, are chosen in a range typical for high quality amorphous passivation layers. 4,7 In order to adjust the oxygen concentration in the films, we varied the gas fraction …”

Section: Sample Preparation and Characterization Methodsmentioning

confidence: 99%

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Analysis of sub-stoichiometric hydrogenated silicon oxide films for surface passivation of crystalline silicon solar cells

Einsele¹,

Beyer²,

Rau³

2012

Journal of Applied Physics

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Thermal stability of passivating layers in amorphous/crystalline silicon (a-Si/c-Si) heterojunction solar cells is crucial for industrial processing and long-term device stability. Hydrogenated amorphous silicon (a-Si:H) yields outstanding surface passivation as atomic hydrogen saturates silicon dangling bonds at the a-Si/c-Si interface. Yet, a-Si surface passivation typically starts to degrade already at annealing temperatures in the range of 200 to 250 °C depending on annealing time, and optical absorption in front layers of a-Si reduces the short circuit current density. We show that oxygen incorporation into a-Si:H films enhances the thermal stability of the passivation and reduces parasitic absorption. We further show that for good passivation of the a-Si/c-Si interface, a compact material structure of the a-Si:O:H films is required where atomic hydrogen is the dominating type of diffusing hydrogen species. For plasma deposited a-Si:O:H films, oxygen incorporation of up to 10 at. % leads to an increase of the optical band gap while the hydrogen concentration is almost constant at approximately 10 at. %. For oxygen concentrations below 3%, the films yield surface recombination velocities as low as 10 cm/s on p-type wafers, and the temperature stability improves by about 50 K compared to pure a-Si:H. For films with relatively low oxygen content, hydrogen effusion spectra and Fourier transform infrared spectroscopy (FTIR) indicate a compact microstructure where only atomic H diffuses. For oxygen concentrations above 3%, the passivation quality reduces and H effusion and FTIR suggest the formation of an open, void-rich material where molecular H2 diffuses. In this case, annealing above 400 °C results in improved interface passivation, presumably due to a densification of the material. Likely, this densification results in an increased density of atomic H, which saturates Si dangling bonds near the c-Si interface.

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Section: Sample Preparation and Characterization Methodsmentioning

confidence: 99%

“…4,5 Apart from conventional hotplate heating, also short time microwave heating has shown beneficial effects on the surface passivation. 5 These results suggest that H plays a dominant role in the surface passivation of c-Si since oxygen or silicon do not diffuse significantly at the annealing temperatures commonly applied.…”

Section: Introductionmentioning

confidence: 99%

Analysis of sub-stoichiometric hydrogenated silicon oxide films for surface passivation of crystalline silicon solar cells

Einsele¹,

Beyer²,

Rau³

2012

Journal of Applied Physics

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“…Tested alternatives to replace the a-Si:H stacks are (microcrystalline) silicon oxides [136,137,182,183] and carbides [148,[184][185][186]. Microcrystalline silicon has a lower but indirect bandgap and features a higher doping efficiency, making it an attractive material for emitter [52,[187][188][189][190] and BSF formation [189,[191][192][193] as well. Of note is that such films may also resolve possible contact problems between TCO-layers and doped films [192,194].…”

Section: Future Directionsmentioning

confidence: 99%

High-efficiency Silicon Heterojunction Solar Cells: A Review

Wolf

Descoeudres

Holman

et al. 2012

Green

763

352

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Abstract. Silicon heterojunction solar cells consist of thin amorphous silicon layers deposited on crystalline silicon wafers. This design enables energy conversion efficiencies above 20% at the industrial production level. The key feature of this technology is that the metal contacts, which are highly recombination active in traditional, diffused-junction cells, are electronically separated from the absorber by insertion of a wider bandgap layer. This enables the record open-circuit voltages typically associated with heterojunction devices without the need for expensive patterning techniques. This article reviews the salient points of this technology. First, we briefly elucidate device characteristics. This is followed by a discussion of each processing step, device operation, and device stability and industrial upscaling, including the fabrication of solar cells with energyconversion efficiencies over 21%. Finally, future trends are pointed out.

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“…Even if current surface recombination velocities may be closer to infinity than to zero, it is certainly possible to decrease surface recombination currents by using band offsets for the respective minorities at the contacts. This concept has been known for a long time in photovoltaics 33 and has been applied in both inorganic 34,35 and organic devices. 36 …”

Section: B Infinite Surface Recombinationmentioning

confidence: 99%

Mobility dependent efficiencies of organic bulk heterojunction solar cells: Surface recombination and charge transfer state distribution

et al. 2009

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Recent simulations of the efficiency of polymer/fullerene solar cells as a function of mobility predicted finite optimum mobilities due to a decrease in open circuit voltage for higher mobilities. We explain this decrease in open circuit voltage with two features of the commonly used model, namely, infinite surface recombination and an integration over a distribution of separation distances of electron and hole in a charge transfer state at the interface between donor and acceptor molecules. Especially, the assumption of a variable electron/hole pair separation at the interface has a considerable influence on the open circuit voltage.

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Low-temperature a-Si:H/ZnO/Al back contacts for high-efficiency silicon solar cells

Cited by 64 publications

References 10 publications

Analysis of sub-stoichiometric hydrogenated silicon oxide films for surface passivation of crystalline silicon solar cells

Analysis of sub-stoichiometric hydrogenated silicon oxide films for surface passivation of crystalline silicon solar cells

High-efficiency Silicon Heterojunction Solar Cells: A Review

Mobility dependent efficiencies of organic bulk heterojunction solar cells: Surface recombination and charge transfer state distribution

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