Showing papers by "Baojie Yan published in 2002"
TL;DR: In this article, the degradation of hydrogenated microcrystalline silicon (μc-Si:H) solar cells was investigated and the authors found that the solar cells made under certain conditions show degradation in air without intentional light soaking.
Abstract: Hydrogenated microcrystalline silicon (μc-Si:H) solar cells are made using modified veryhigh-frequency (MVHF) glow discharge at deposition rates ∼3-5 A/s. We find that the solar cells made under certain conditions show degradation in air without intentional light soaking. The short-circuit current drops significantly within a few days after deposition, and then stabilizes. We believe that post-deposition oxygen diffusion along the grain boundaries or cracks is the origin of the ambient degradation. By optimizing the deposition conditions, we have found a plasma regime in which the μc-Si:H solar cells do not show such ambient degradation. The best a-Si:H/μc-Si:H double-junction solar cell has an initial active-area efficiency of 10.9% and is stable against the ambient degradation. The stability data of the solar cells after light soaking are also presented.
14 citations
TL;DR: In this paper, the authors observed a significant light-induced increase in the open-circuit voltage, Voc, of thin-film silicon solar cells whose intrinsic layer consists of an amorphous and micro-crystalline mixed phase.
Abstract: We observe a significant light-induced increase in the open-circuit voltage, Voc, of thin-film silicon solar cells whose intrinsic (i) layer consists of an amorphous and microcrystalline mixed phase. The increase depends on the i-layer thickness, the i-layer deposition temperature, the initial Voc values, and the light-soaking intensity. An increase of as large as 150 mV is observed. The original Voc is restored after subsequent thermal annealing. In-situ photoluminescence (PL) spectroscopy is used to investigate this metastable phenomenon. We find that the PL intensity and peak-energy position associated with the amorphous component of the heterogeneous material increase upon light soaking, suggesting a structural change. We propose that a reduction of microcrystalline volume fraction or size is responsible for the Voc enhancement.
10 citations
19 May 2002
TL;DR: In this paper, the effect of applying a reverse bias to the cell during light soaking was examined and it was shown that the variation in V/sub oc/ is greatly suppressed. And subjecting the heterogeneous cells to a forward bias in the dark causes an enhancement in V /sub o c/, similar to the open-circuit light-soaking effect.
Abstract: We recently reported on a significant light-induced enhancement in the open-circuit voltage (V/sub oc/) of heterogeneous silicon solar cells whose intrinsic layer consists of a mixture of amorphous and microcrystalline silicon phases. In this study, we examine the effect of applying a reverse bias to the cell during light soaking and discover that the variation in V/sub oc/ is greatly suppressed. In addition, we find that subjecting the heterogeneous cells to a forward bias in the dark causes an enhancement in V/sub oc/, similar to the open-circuit light-soaking effect. Based on these two experiments, we conclude that the cause of the V/sub oc/ enhancement is the same as that of the Staebler-Wronski effect.
2 citations
TL;DR: In this paper, the second harmonic detection (SH-ESR) of the ESR was used to detect the decay of tetrahedrally coordinated amorphous semiconductors.
Abstract: The decay of optically excited electrons and holes in tetrahedrally coordinated amorphous semiconductors is a universal property of these amorphous solids [Phys. Rev. Lett. 84 (2000) 4180]. The experimental measurements employ a seldom-used electron spin resonance (ESR) detection technique that surpasses the sensitivity of previous measurements by several orders of magnitude. This technique employs second harmonic detection (SH-ESR) of the ESR. Measurements have been performed over a wide range of excitation intensities (nW/cm2 to W/cm2) on hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous germanium (a-Ge:H). Using the SH-ESR technique, the kinetics can be studied down to saturated carrier densities as low as approximately 10 14 cm −3 . In addition to the long-time decay curves, both the saturated densities of carriers after long-time irradiation and the most probable recombination lifetimes for the optically excited carriers in a-Si:H agree well with models for the universal diffusion and recombination of carriers at low temperatures. Similar results are obtained for samples of a-Ge:H with germanium dangling-bond densities ≲10 17 cm −3 . A comparison of the ESR lineshapes for the electrons and holes trapped in the conduction and valence band tails, respectively, with electrons and holes trapped in a divacancy in crystalline silicon shows that the asymmetries and localizations of the wavefunctions are similar in both cases.