Interface recombination in heterojunctions of amorphous and crystalline silicon
TL;DR: In this paper, it was shown that the form of the I-V characteristics and the effective interface recombination velocity depend on the treatment of the Si-wafer prior to the deposition of the amorphous emitter.
Abstract: Heterojunction solar cells consisting of an n-type a-Si:H(n) emitter and a p-type monocrystalline silicon wafer have been studied with particular emphasis on the role of interface recombination. It is shown that the form of the I – V characteristics and the effective interface recombination velocity depend on the treatment of the Si-wafer prior to the deposition of the amorphous emitter. Numerical simulation suggests that the non-exponential (S-shape) dependence of the I – V curves under illumination arises from a high density of interface states which results in enhanced recombination via interface states.
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TL;DR: In this article, the authors have fabricated hydrogenated amorphous silicon (aSi:H)∕crystalline silicon (cSi) heterojunction solar cells with different aSi:h layer thicknesses, in order to determine effects of aSiH2-rich interface structure formed at the aµ:H∕cµ heterointerface.
Abstract: We have fabricated hydrogenated amorphous silicon (a‐Si:H)∕crystalline silicon (c‐Si) heterojunction solar cells with different a‐Si:H layer thicknesses, in order to determine effects of a‐Si:H layer thicknesses on the performance of a‐Si:H∕c‐Si solar cells The thicknesses of a‐Si:H p‐i layers formed on a n-type c‐Si substrate were controlled accurately on the atomic scale by applying real-time spectroscopic ellipsometry during the a‐Si:H growth With increasing a‐Si:H p‐i layer thicknesses, the open-circuit voltage (Voc) and fill factor increase drastically up to 40A (i layer) and 30A (p layer), whereas the short-circuit current density (Jsc) reduces gradually By using optimum a‐Si:H layer thicknesses (i∕p=40∕30A), we obtained a solar cell efficiency of 161% without incorporating surface texture and a back-surface field structure Quite interestingly, the optimum a‐Si:H i-layer thickness (40A) shows good correlation with a SiH2-rich interface structure formed at the a‐Si:H∕c‐Si heterointerface, sugges
204 citations
01 Jan 2012
TL;DR: In this paper, a-Si:H/c-Si heterojunction and other high efficiency solar cells: a comparison of rear contact cells are presented. But the authors do not provide a detailed description of the interaction between the two heterojunctions.
Abstract: Foreword.- Introduction.- Status of heterojunction solar cell R&D.- Basic features of Heterojunctions illustrated by selected experimental methods and results.- Deposition methods of thin film silicon.- Electronic properties of ultrathin a-Si:H layers and the a-Si:H/c-Si interface.- Degradation of (bulk and thin film) a-Si and interface passivation.- Photoluminescence and electroluminescence for a Si:H/c Si device and interface characterization.- Deposition and properties of transparent conductive oxides.- Metallization and formation of contacts.- Electrical and optical characterization of a-Si:H/c Si cells.- Wet-chemical pre-treatment of c Si for a-Si:H/c-Si heterojunctions.- Theory of heterojunctions and the determination of band offsets from electrical measurements.- Modeling and simulation of a Si:H/c Si cells.- Surface passivation using ALD Al2O3.- Introduction to AFORS-HET.- Hands-on experience with simulation tools.- a-Si:H/c-Si heterojunction and other high efficiency solar cells: a comparison.- Rear contact cells.- Progress in systematic industrialization of Hetero-Junction-based Solar Cell technology.
190 citations
TL;DR: In this paper, the conduction mechanisms and temperature dependence of HIT (heterojunction with intrinsic thin layer) structure solar cells while changing the thickness of the undoped amorphous silicon layer were evaluated.
Abstract: We evaluated the conduction mechanisms and temperature dependence of HIT (heterojunction with intrinsic thin layer) structure solar cells while changing the thickness of the undoped amorphous silicon layer. It was confirmed that the diffusion model determined the carrier transport property of this device at the high-forward-bias region (0.4
130 citations
TL;DR: In this paper, temperature-dependent measurements of I-V curves in the dark and under illumination are presented to elucidate the dominant transport mechanisms in amorphous silicon-crystalline silicon (a-Si:H/c-Si) heterojunction solar cells.
Abstract: We present temperature-dependent measurements of I-V curves in the dark and under illumination in order to elucidate the dominant transport mechanisms in amorphous silicon-crystalline silicon (a-Si:H/c-Si) heterojunction solar cells. ZnO:Al/(p)a-Si:H/(n)c-Si/(n+)a-Si:H cells are compared with inversely doped structures and the impact of thin undoped a-Si:H buffer layers on charge carrier transport is explored. The solar cell I-V curves are analyzed employing a generalized two-diode model which allows fitting of the experimental data for a broad range of samples. The results obtained from the fitting are discussed using prevalent transport models under consideration of auxiliary data from constant-final-state-yield photoelectron spectroscopy, surface photovoltage, and minority carrier lifetime measurements. Thus, an in-depth understanding of the device characteristics is developed in terms of the electronic properties of the interfaces and thin films forming the heterojunction. It is shown that dark I-V curve fit parameters can unequivocally be linked to the open circuit voltage under illumination which opens a way to a simplified device assessment.
113 citations
TL;DR: In this paper, three approaches to improve the fill factor of IBC-SHJ solar cells are proposed: reduced thickness, increased conductivity, and reduced band gap, which is related to the energy barrier at the hetero-interface.
Abstract: Interdigitated back contact silicon heterojunction (IBC-SHJ) solar cells have the potential for high open circuit voltage (VOC) due to the surface passivation and heterojunction contacts, and high short circuit current density (JSC) due to all back contact design. Intrinsic amorphous silicon (a-Si:H) buffer layer at the rear surface improve the surface passivation hence VOC and JSC, but degrade fill factor (FF) from an “S” shape J–V curve. Two-dimensional (2D) simulation using “Sentaurus device” demonstrates that the low FF is related to the valence band offset (energy barrier) at the hetero-interface. Three approaches to the buffer layer are suggested to improve the FF: (1) reduced thickness, (2) increased conductivity, and/or (3) reduced band gap. Experimental IBC-SHJ solar cells with reduced buffer thickness ( 23% are possible on planar devices with optimized pitch dimensions and achievable surface passivation, and 26% with light trapping. This work provides criterion to design IBC-SHJ solar cell structures and optimize cell performance. Copyright © 2010 John Wiley & Sons, Ltd.
86 citations
Cites methods from "Interface recombination in heteroju..."
...Various explanations for the origin of the S-shape J–V curve have been proposed, including carrier recombination due to interface defects [14,15], recombination in the c-Si...
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TL;DR: A new type of a-Si/c-Si heterojunction solar cell, called the HIT (Heterojunction with Intrinsic Thin-layer) solar cell has been developed based on ACJ (Artificially Constructed Junction) technology as mentioned in this paper.
Abstract: A new type of a-Si/c-Si heterojunction solar cell, called the HIT (Heterojunction with Intrinsic Thin-layer) solar cell, has been developed based on ACJ (Artificially Constructed Junction) technology. A conversion efficiency of more than 18% has been achieved, which is the highest ever value for solar cells in which the junction was fabricated at a low temperature (<200°C).
540 citations
TL;DR: In this paper, a new experimental method for determining band lineups at the semiconductor heterojunctions was presented and applied to the $censuremath{-}\mathrm{S}\mathm{i}\left(100\right)/a \ensurem{-}-S}\m{S} \mathm{\m{m} \m{h} \h] :mathm {H}$ heterostructure, where the photoelectric yield spectroscopy excited with photons in the near UV range.
Abstract: We present a new experimental method for determining band lineups at the semiconductor heterojunctions and apply it to the $c\ensuremath{-}\mathrm{S}\mathrm{i}\left(100\right)/a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ heterostructure. This method uses a modern version of an old spectroscopy: the photoelectric yield spectroscopy excited with photons in the near UV range. It is shown that both substrate and overlayer valence-band tops can be identified in the yield spectrum due to the high escape depth and the high dynamical range of the technique, thus allowing a direct and precise determination of the band lineup. A value of $\ensuremath{\Delta}{E}_{V}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.44\ifmmode\pm\else\textpm\fi{}0.02\mathrm{eV}$ was found for the valence band discontinuity.
86 citations
TL;DR: In this paper, the influence of preparation-induced surface roughness, as well as the hydrogen and oxide coverage on electronic properties of Si(111) and Si(100) surfaces was investigated by combining various surface-sensitive techniques.
Abstract: The influence of preparation-induced surface roughness, as well as the hydrogen and oxide coverage on electronic properties of Si(111) and Si(100) surfaces was investigated by combining various surface-sensitive techniques. Simultaneous surface photovoltage (SPV) and spectroscopic ellipsometry (SE) measurements, both in the ultraviolet/visible (UV–VIS) and the infrared (IR) spectroscopic region, yielded detailed information about intrinsic and extrinsic surface states on hydrogen (H)-terminated Si(111) and Si(100) surfaces, immediately after the wet-chemical preparation as well as during the initial oxidation. The energetic distributions of interface states D it ( E ) on Si(100) and Si(111) surfaces were correlated to the surface roughness 〈 d r 〉, the change of hydrogen coverage and the oxide growth on an atomic scale. As shown by these experiments, generally higher interface state densities D it, min were observed on Si(100) surfaces in comparison to Si(111). However, on Si(100) substrates a faster oxide growth and a significantly thicker final native oxide layer were found. The wet-chemical preparation methods of hydrogen or oxide passivated surfaces on Si(100) substrates were carefully optimized, resulting in smooth H-terminated surfaces (〈 d r 〉≈4 A and D it, min 10 cm −2 eV −1 ) and passivating oxide layers in the thickness range of 1–3 nm ( D it, min 11 eV −1 cm −2 ).
57 citations