Impact of Maxwell rigidity transitions on resistance drift phenomena in GexTe1x glasses (original) (raw)
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Solar Energy Materials and Solar Cells, 2014
We briefly review the basic concepts of junction capacitance and the peculiarities related to amorphous semiconductors, paying tribute to Cohen and to his pioneering work. We extend the discussion to very high efficiency silicon heterojunction (SiHET) solar cells where both an amorphous semiconductor, namely hydrogenated amorphous silicon, and heterojunctions are present. By presenting both modeling and experimental results, we demonstrate that the conventional theory of junction capacitance based on the depletion approximation in the space charge region, cannot reproduce the capacitance data obtained on SiHET cells. The experimental temperature dependence is significantly stronger than that of the depletion-layer capacitance, while the bias dependence yields underestimated values of the diffusion potential, leading to strong errors if applied to the determination of band offsets using the procedure proposed precedingly in the literature. We demonstrate that this is not related to the amorphous nature of a-Si:H, but to the existence of a strongly inverted c-Si surface layer that requires minority carriers to be taken into account in the analysis of the junction capacitance.
Journal of Applied Physics, 2015
We develop a fully analytical model in order to describe the temperature dependence of the low frequency capacitance of heterojunctions between hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). We demonstrate that the slope of the capacitance-temperature (C-T) curve is strongly enhanced if the c-Si surface is under strong inversion conditions compared to the usually assumed depletion layer capacitance. We have extended our analytical model to integrate a very thin undoped (i) a-Si:H layer at the interface and the finite thickness of the doped a-Si:H layer that are used in high efficiency solar cells for the passivation of interface defects and to limit short circuit current losses. Finally, using our calculations, we analyze experimental data on high efficiency silicon heterojunction solar cells. The transition from the strong inversion limited behavior to the depletion layer behavior is discussed in terms of band offsets, density of states in a-Si:H, and work function of the indium tin oxide (ITO) front electrode. In particular, it is evidenced that strong inversion conditions prevail at the c-Si surface at high temperatures down to 250 K, which can only be reproduced if the ITO work function is larger than 4.7 eV. V
The paper deals with the diagnostics of structures containing a heterojunction of amorphous and crystalline silicon representing the key part of the silicon heterojunction solar cell. The change of carrier inversion at the heterointerface by means of an intrinsic amorphous intermediate layer inserted at the heterointerface was confirmed by capacitance deep level transient spectroscopy and coplanar conductance measurements. A growing thickness of the intrinsic amorphous silicon layer brings about a decrease in the thickness of the inversion layer at the heterointerface, leading to higher recombination. The results emphasize the requirement for optimization of the interface with the regard to the trade-off between the thickness of the passivation layer and interface quality.
Characterization of silicon heterojunctions for solar cells
Nanoscale Research Letters, 2011
Conductive-probe atomic force microscopy (CP-AFM) measurements reveal the existence of a conductive channel at the interface between p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) as well as at the interface between n-type a-Si:H and p-type c-Si. This is in good agreement with planar conductance measurements that show a large interface conductance. It is demonstrated that these features are related to the existence of a strong inversion layer of holes at the c-Si surface of (p) a-Si:H/(n) c-Si structures, and to a strong inversion layer of electrons at the c-Si surface of (n) a-Si:H/(p) c-Si heterojunctions. These are intimately related to the band offsets, which allows us to determine these parameters with good precision.
IEEE Journal of Photovoltaics, 2018
We have analyzed a-Si:H(p)/a-Si:H(i)/c-Si(n) heterojunction silicon solar cell having the S-shaped current densityvoltage characteristics with a low fill factor and open-circuit voltage, using quantum efficiency (QE) characterization technique under forward/reverse voltage and different light (blue, infrared, and white) bias conditions. The curvature of S-shape is sensitive to excitation light intensities because of modification in junction barrier potential (variation in quasi-Fermi levels splitting). With forward-bias voltage alone near/above S-shaped region, cell's QE is uniformly reduced because of reduction in junction field and dominance of barrier for collection of holes. However, with blue and white light at bias voltages close to S-shaped characteristics, a uniform improvement of QE in broad wavelength region is observed because of defects saturation at the junction interface and photoconductivity in the a-Si layers. With white light and voltage bias, cell's QE is anomalously improved and it has even crossed the QE response at no voltage/light bias conditions in the blue region because of defects saturation in a-Si:H layers, whereas under infrared light and voltage bias conditions defect saturation is not displayed in the QE because of carrier generation in a deeper region of the cell after crossing unabsorbed photons front region.
International Journal of Photoenergy, 2021
Photovoltaic devices based on amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction interfaces hold the highest efficiency as of date in the class of silicon-based devices with efficiencies exceeding 26% and are regarded as a promising technology for large-scale terrestrial PV applications. The detailed understanding behind the operation of this type of device is crucial to improving and optimizing its performance. SHJ solar cells have primarily two main interfaces that play a major role in their operation: the transparent conductive oxide (TCO)/a-Si:H interface and the a-Si:H/c-Si heterojunction interface. In the work presented here, a detailed analytical description is provided for the impact of both interfaces on the performance of such devices and especially on the device fill factor ( ). It has been found that the TCO work function can dramatically impact the by introducing a series resistance element in addition to limiting the forward biased current under illumin...
Journal of The …, 2011
The fabrication of amorphous silicon/crystalline silicon ͑a-Si:H/c-Si͒ heterojunction solar cell and an understanding of the fundamental conduction mechanism in the device are presented. In the first part, the effect of intrinsic amorphous silicon ͓a-Si:H͑i͔͒ layer thickness on the performance of a-Si:H/c-Si solar cells has been studied. The thickness of a-Si:H͑i͒ layer formed on n-type c-Si substrate was controlled accurately with spectroscopy ellipsometry ͑SE͒. Based on SE results, we discuss the influence of the a-Si:H͑i͒ thickness on the interface quality and thereby cell performance. Then, in the latter part, we present the temperaturedependent current density-voltage curves, in the dark, in order to elucidate the dominant transport mechanisms in a-Si:H/c-Si heterojunction solar cells with and without incorporation of a-Si:H͑i͒ layers. Finally, using optimum design considerations, we obtained a solar cell efficiency of 17.43%.