Towards high-efficiency thin-film silicon solar cells with the “micromorph” concept

Meier, J.; Dubail, S.; Platz, R.; Torres, P.; Kroll, U.; Selvan, J. A. Anna; Vaucher, N. Pellaton; Hof, C.; Fischer, D.; Keppner, H.; Flückiger, R.; Shah, A.; Shklover, Valery; Ufert, K.‐D.

doi:10.1016/s0927-0248(97)00173-6

Cited by 111 publications

(49 citation statements)

References 9 publications

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“…The measurement confirms the enhanced stability against light-soaking for films deposited with hydrogen dilution [17]. In fact, the H 2 -diluted i-layers at T s =220°C have successfully been incorporated into a-Si:H/a-Si:H stacked cells and as top cells in micromorph tandem cells resulting in stabilized efficiencies of 9% [2] and 10.7% [1] respectively. The purpose of this work is to further enhance the efficiency of micromorph tandem cells by increasing the optical absorption in the top cell i-layer.…”

Section: Electronical Properties and Degradation Behaviorsupporting

confidence: 68%

“…amorphous silicon / microcrystalline silicon (a-Si:H/µc-Si:H) tandem cells, are continuously gaining in interest as promising thin-film silicon solar cells. 10.7% stabilized efficiency has been achieved so far [1] (as confirmed by the Fraunhofer Institut für Solare Energiesysteme, Freiburg/Germany). There is a high potential for a further increase of the stabilized efficiency for such micromorph tandem cells.…”

Section: Introduction / Motivationmentioning

confidence: 59%

“…We have previously demonstrated a 10.7% stable micromorph tandem cell [1]. The characteristic data of this cell were V oc =1.34V, FF=66.7% and I sc =11.9mA/cm 2 .…”

Section: Micromorph Tandem Cells With High-t S Top Cellsmentioning

confidence: 91%

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High-Ts amorphous top cells for increased top cell currents in micromorph tandem cells

Platz

Hof

Fischer

et al. 1998

Solar Energy Materials and Solar Cells

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In the present paper, the authors discuss the application of amorphous p-i-n solar cells containing i-layers which are deposited at high substrate temperatures as top cells in amorphous/microcrystalline tandem ("micromorph") solar cells. Increasing the substrate temperature for the deposition of intrinsic a-Si:H results in a reduced optical gap. The optical absorption is enhanced and thereby the current generation. A high current generation within a relatively thin amorphous top cell is very interesting in the context of micromorph tandem cells, where the amorphous top cell should contribute a current of at least 13mA/cm 2 for a total cell current density of 26mA/cm 2 .A detailed study is presented of the intrinsic material deposited by VHF-GD at 70 MHz at substrate temperatures between 220°C and 360°C, including samples deposited from hydrogen-diluted silane plasmas. The stability of the films against light soaking is investigated employing the µ 0 τ 0 parameter, which has been shown to be directly correlated to the cell performance.The paper discusses in detail the technological problems arising from the insertion of ilayers deposited at high substrate temperatures into solar cells. These problems are specially pronounced in the case of cells in the p-i-n (superstrate) structure. The authors demonstrate that an appropriate interface layer at the p/i-interface can largely reduce the detrimental effects of i-layer deposition at high temperatures.Finally, the application of such optimized high-temperature amorphous cells as (a) bottom cells in a-Si:H/a-Si:H stacked cells and (b) as top cells in micromorph tandem cells is discussed. Current densities of 13mA/cm 2 in the top cell are available with a top cell i-layer thickness of only 250nm. The potential of such top cells for raising the stabilized efficiency of micromorph tandem cells is discussed.

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Section: Electronical Properties and Degradation Behaviorsupporting

confidence: 68%

Section: Introduction / Motivationmentioning

confidence: 59%

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High-Ts amorphous top cells for increased top cell currents in micromorph tandem cells

Platz

Hof

Fischer

et al. 1998

Solar Energy Materials and Solar Cells

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“…However, its major use is in micromorph tandem cells, which consist in a stacked of amorphous and microcrystalline cells [2] which can reach stabilized efficiencies above 11% [3,4]. In mc-Si:H cells, zones of porous material, called thereafter cracks, appear typically when the device is deposited on substrates with Vshape morphology (i.e., sharp and steep valleys) [5][6][7][8], as is usually needed to achieve good light trapping properties.…”

Section: Introductionmentioning

confidence: 99%

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Python

Dominé

Söderström

et al. 2010

Progress in Photovoltaics

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Microcrystalline silicon (mc-Si:H) cells can reach efficiencies up to typically 10% and are usually incorporated in tandem micromorph devices. When cells are grown on rough substrates, ''cracks'' can appear in the mc-Si:H layers. Previous works have demonstrated that these cracks have mainly detrimental effects on the fill factor and open-circuit voltage, and act as bad diodes with a high reverse saturation current. In this paper, we clarify the nature of the cracks, their role in postoxidation processes, and indicate how their density can be reduced. Regular secondary ion mass spectrometry (SIMS) and local nano-SIMS measurements show that these cracks are prone to local post-oxidation and lead to apparent high oxygen content in the layer. Usually the number of cracks can be decreased with an appropriate modification of the substrate surface morphology, but then, the required light scattering effect is reduced due to a lower roughness. This study presents an alternative/complementary way to decrease the crack density by increasing the substrate temperature during deposition. These results, also obtained when performing numerical simulation of the growth process, are attributed to the enhanced surface diffusion of the adatoms at higher deposition temperature. We evaluate the cracks density by introducing a fast method to count cracks with good statistics over approximately 4000 mm of sample cross-section. This method is proven to be useful to quickly visualize the impact of substrate morphology on the density of cracks in microcrystalline and in micromorph devices, which is an important issue in the manufacturing process of modules.

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“…Nevertheless, this disturbing n-type character could, in recent work, 5,6 be compensated by ''microdoping''; thereby, ''midgap'' c-Si:H ͑Fermi level at midgap͒ was obtained and successfully implemented in a fully microcrystalline photovoltaic device. [7][8][9] However, the microdoping technique which consists of adding diborane in the parts per million ͑ppm͒ range into the gas phase during deposition, is unfortunately difficult to handle; in fact, it has been observed that the Fermi level position reacted thereby sensitively to the deposition rate, to the outgassing of the reactor and to feedgas purity. Thus, this delicate compensation technique is not of real interest for potential industrial applications.…”

mentioning

confidence: 99%

Device grade microcrystalline silicon owing to reduced oxygen contamination

Torres

Meier

Flückiger

et al. 1996

Applied Physics Letters

Self Cite

181

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As-deposited undoped microcrystalline silicon (μc-Si:H) has in general a pronounced n-type behavior. Such a material is therefore often not appropriate for use in devices, such as p-i-n diodes, as an active, absorbing i layer or as channel material for thin-film transistors. In recent work, on p-i-n solar cells, this disturbing n-type character had been successfully compensated by the ‘‘microdoping’’ technique. In the present letter, it is shown that this n-type behavior is mainly linked to oxygen impurities; therefore, one can replace the technologically delicate microdoping technique by a purification method, that is much easier to handle. This results in a reduction of oxygen impurities by two orders of magnitude; it has, furthermore a pronounced impact on the electrical properties of μc-Si:H films and on device performance, as well. Additionally, these results prove that the unwanted donor-like states within μc-Si:H are mainly due to extrinsic impurities and not to structural native defects.

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Towards high-efficiency thin-film silicon solar cells with the “micromorph” concept

Cited by 111 publications

References 9 publications

High-Ts amorphous top cells for increased top cell currents in micromorph tandem cells

High-Ts amorphous top cells for increased top cell currents in micromorph tandem cells

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Device grade microcrystalline silicon owing to reduced oxygen contamination

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