Gettering in PolySi/SiOx Passivating Contacts Enables Si-Based Tandem Solar Cells with High Thermal and Contamination Resilience (original) (raw)
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Monolithic thin-film chalcogenide–silicon tandem solar cells enabled by a diffusion barrier
Solar Energy Materials and Solar Cells, 2020
Following the recent success of monolithically integrated Perovskite/Si tandem solar cells, great interest has been raised in searching for alternative wide bandgap top-cell materials with prospects of a fully earthabundant, stable and efficient tandem solar cell. Thin film chalcogenides (TFCs) such as the Cu 2 ZnSnS 4 (CZTS) could be suitable top-cell materials. However, TFCs have the disadvantage that generally at least one high temperature step (> 500 • C) is needed during the synthesis, which could contaminate the Si bottom cell. Here, we systematically investigate the monolithic integration of CZTS on a Si bottom solar cell. A thermally resilient double-sided Tunnel Oxide Passivated Contact (TOPCon) structure is used as bottom cell. A thin (< 25 nm) TiN layer between the top and bottom cells, doubles as diffusion barrier and recombination layer. We show that TiN successfully mitigates in-diffusion of CZTS elements into the c-Si bulk during the high temperature sulfurization process, and find no evidence of electrically active deep Si bulk defects in samples protected by just 10 nm TiN. Post-process minority carrier lifetime in Si exceeded 1.5 ms, i.e., a promising implied open-circuit voltage (i-V oc) of 715 mV after the high temperature sulfurization. Based on these results, we demonstrate a first proof-of-concept two-terminal CZTS/Si tandem device with an efficiency of 1.1% and a V oc of 900 mV. A general implication of this study is that the growth of complex semiconductors on Si using high temperature steps is technically feasible, and can potentially lead to efficient monolithically integrated two-terminal tandem solar cells.
Energy Procedia, 2017
Within this work, both the performance and reliability of industrial p-type monocrystalline solar cells with dielectrically passivated rear side and corresponding modules are investigated. Results of the mass production of Q.ANTUM solar cells at Hanwha Q CELLS on boron-doped p-type Czochralski-grown silicon (Cz-Si) substrates are presented, exceeding 21.5 % average conversion efficiency. Without power-enhancing measures such as the use of half cells, multi-wire approaches or light-capturing ribbons, essentially all currently (as of March 2017) produced Cz-Si Q.ANTUM solar modules exhibit output powers of > 300 Wp with 60 full 4-busbar cells. In terms of reliability, light-induced degradation (LID) is investigated in detail, with conditions relevant for the activation of, both, the boron-oxygen (BO) defect, and, so-called "Light and Elevated Temperature Induced Degradation" (LeTID). While the formation of the BO defect has been considered the most prominent LID mechanism in boron-doped p-type Cz-Si, LeTID has so far been discussed mainly as a potential issue for passivated emitter and rear cells (PERC) on multicrystalline silicon (mc-Si) substrates. This work shows that, if not adequately suppressed, LeTID can also occur in p-type Cz-Si PERC with a degradation in output power of up to > 6 %, which cannot be suppressed in a straightforward manner by conventional processing steps to permanently deactivate the BO defect. In contrast to conventional PERC, Hanwha Q CELLS' Q.ANTUM technology is shown to reliably suppress, both, LID due to BO defect formation, and LeTID in modules manufactured from, both, p-type mc-Si and Cz-Si substrates.
Application of CMOS metal barriers to copper plated silicon solar cells
In this paper, alternative front-side metallization schemes for c-Si solar cells are investigated. These are based on the sputtering of different metal barriers followed by copper electroplating. Different emitters have been evaluated. The influence of the plating process and the impact of different barrier materials on contact resistance, plating properties and device reliability are also investigated. Using this approach, large area silicon solar cells with conversion efficiencies up to 19.4% are obtained on Cz material. First results on the application of these deposition techniques in a low-cost industrial compatible process flow show a conversion efficiency of 18.5%.
IEEE Journal of Photovoltaics, 2016
CZTS thin film solar cells have been qualified as potential competitors of the more established CIGS ones. One of the more important handicaps of CZTS solar cells is the opencircuit voltage deficit. The rear-contact/absorber interface is known to be very sensitive to the formation of secondary phases, which are detrimental for the electrical behavior of the photovoltaic devices. The addition of intermediate layers to favor the formation of an adequate interface has been repeatedly tested. In this work, an amorphous silicon carbide (a-SiC) layer is added to explore its influence on the material properties and electrical performance of CZTSe solar cells. According to SEM analysis, when the a-SiC layer thickness is increased, bigger grains along the absorber are obtained. Additionally, a lower [V Cu +Zn Cu ] defect cluster density is also deduced from the analysis of Raman measurements. Both results indicate a favorable impact of a-SiC films on the material quality of the absorber. Fabricated solar cells show an enhancement of 0.9% abs. of efficiency compared to identical solar cells without a-SiC layers used as a reference. This increase is mainly related to an improvement of open-circuit voltage and fill factor when the proposed intermediate layer is included. Index Terms-Silicon carbide, Cu 2 ZnSn(S 1-y Se y) 4 , thin-film solar cells, surface passivation layer. I. INTRODUCTION HE Cu 2 ZnSn(S 1-y Se y) 4 (CZTS) solar cells are already a potential alternative to more mature CuIn x Ga 1-x Se 2 (CIGS) ones due to their reduced environmental impact and the relatively lower cost because of the abundance of their Manuscript received March 4, 2016.
Solar Energy Materials and Solar Cells, 2011
Solar grade, p-type multicrystalline silicon wafers with large grains from different parts of silicon ingots produced by the metallurgical route (SoG-Si) at ELKEM Solar were studied using a number of complementary methods such as microwave photoconductivity decay, deep level transient spectroscopy, transmission and scanning electron microscopy, X-ray fluorescence, and secondary ion mass spectroscopy. Wafers from the top of the ingots have uniform spatial distributions of both minority carrier lifetime (average lifetime t¼3.2 ms) and concentrations of illumination-sensitive recombination centers (N rc ¼ 3 Â 10 10 À 2 Â 10 11 cm À 3) over the whole wafers. Wafers from the bottom of the ingots have regions of very low lifetimes (t ¼ 0.3 ms) and high concentrations of illumination-sensitive recombination centers (N rc ¼2 Â 10 12 cm À 3). In the top part of the ingots the observed DLTS peaks can be attributed to copper-related extended defects, and the DLTS results from grains and grain boundaries are not significantly different. The main factors limiting the lifetime in the high lifetime regions are concluded to be illumination-sensitive recombination centers such as Fe-B pairs, B-O complexes, and Cu-related extended defects. The low lifetimes in the bottom part of the ingots are explained by a combination of several factors including high concentrations of illumination-sensitive recombination centers and of some deleterious elements (S, Na and Al), and a large amount of structural defects.
The impact of interstitial Fe contamination on n-type Cz-Silicon for high efficiency solar cells
Solar Energy Materials and Solar Cells, 2020
In this work, we have investigated the impact of interstitial Fe contamination on the effective minority carrier lifetime of n-type Cz silicon bulk material for high efficiency solar cells. The study covers a Fe concentration in the silicon bulk from 3.5 � 10 12 cm-3 to 2.7 � 10 14 cm-3. We have added 5 different concentrations (30, 100, 300, 1000 and 3000 ppb) of Fe intentionally to a wet chemical process tank and measured the transfer to the silicon wafer surface mimicking a possible contamination during wet chemical processing. In order to fabricate carrier lifetime test vehicles, the silicon wafer is then passivated with thermal silicon oxide from both sides. The surface contamination is driven into the bulk by mimicking a high temperature process during solar cell manufacturing. Effective minority carrier lifetime is measured at injection levels from 1 � 10 13 cm-3 to 3 � 10 15 cm-3. We have fitted the theoretical curve for interstitial Fe derived from the SRH theory to the measured values and extracted the Fe contamination concentration. This value is comparable to the calculated value extracted from the surface contamination measurement. For low level injection (LLI), we extracted the capture cross section for interstitial Fe to be 6.45 � 10-17 cm/s � 2.23 � 10-17 cm/s. The measured Fe contamination levels are used for the conversion efficiency fitting of a n-type bifacial silicon solar cell using QUOKKA simulations. The simulations show that very low Fe contamination concentrations of [Fe] bulk ¼ 3.5 � 10 12 cm-3 ([Fe] surf ¼ 6 � 10 10 cm-2) already degrade the solar cell efficiency by 10% relative.
Renewable Energy, 2000
The eect of the annealing ambient on the eciency of the phosphorous gettering process for Czochralski (CZ) silicon wafers is investigated in this paper. Phosphorous is diused from a POCl 3 source at dierent temperatures into single-crystal p-type silicon wafers having a resistivity of around 1 ohm/cm. This is followed by an additional heat treatment in either oxidizing (wet and dry oxide) or in inert (argon) ambient. The laser microwave photoconductivity decay method is used to monitor the changes in the minority carrier lifetime after the phosphorous diusion and the subsequent annealing. Furthermore, solar cells are fabricated on the treated samples in order to correlate the lifetime measurements with the illuminated I-V characteristics of the cells. 7
Industrial Si Solar Cells With Cu-Based Plated Contacts
IEEE Journal of Photovoltaics, 2015
Until today, most industrial c-Si solar cells have been limited by front emitter and front metal contact properties. This study demonstrates that laser ablation and inline plating of nickel and copper followed by inline thermal annealing results in improved performance and reduced cost. Stable efficiencies exceeding 20.8% on p-type PERC CZ-Si solar cells have been independently confirmed by FhG-ISE CalLab. Average fill factors up to 80.8% have been demonstrated on large-area solar cells with a homogeneous emitter P surface concentration below 4 × 10 19 P/cm 3. Reliable module performance according to the IEC61215 standard is reported.
Impurity-Related Limitations of Next-Generation Industrial Silicon Solar Cells
We apply highly predictive 2-D device simulation to assess the impact of various impurities on the performance of nextgeneration industrial silicon solar cells. We show that the lightinduced boron-oxygen recombination center limits the efficiency to 19.2% on standard Czochralski-grown silicon material. Curing by illumination at elevated temperature is shown to increase the efficiency limit by +1.5% absolute to 20.7%. In the second part of this paper, we examine the impact of the most important metallic impurities on the cell efficiency for p-and n-type cells. It is widely believed that solar cells on n-type silicon are less sensitive to metallic impurities. We show that this statement is not generally valid as it is merely based on the properties of Fe but does not account for the properties of Co, Cr, and Ni.
Energy Procedia, 2011
We model currently fabricated industrial-type screen-printed boron-doped Cz silicon solar cells using a combination of process and device simulations. The model reproduces the experimental results precisely and allows us to predict both the efficiency gain after specific cell improvements and the associated thermal budgets. Separating the resistive losses (evaluated for various contributions) from the recombination losses (evaluated in different device regions) allows us to forecast the improvements of the emitter and the rear side necessary such that the recombination losses in the base dominate. We predict that to increase cell efficiency considerably beyond 19.7 %, the base material needs to be improved.