Simulation-based Efficiency Gain Analysis of 21.2%-efficient Screen-printed PERC Solar Cells

Passivated Emitter and Rear Cells (PERC) with efficiencies well above 20% are likely to become the next mass production technology. A quantification of all power loss mechanisms of such industrial PERC cells is helpful in prioritizing future efficiency improvement measures. We report on a numerical simulation of the power losses of a 21.2%-efficient industrial PERC cell using extensive experimental input data. Our synergetic efficiency gain analysis relies on deactivating single power loss mechanisms in the simulation at a time to access the full potential power gain related to that mechanism. The complete analysis therefore explains the efficiency gap between the industrial PERC solar cell and the theoretical maximum efficiency of a crystalline Si solar cell. Based on the simulations, the largest single loss mechanism is front grid shadowing followed by recombination in the emitter and its surface. All individual resistive losses, all individual optical losses and all (avoidable) individual recombination losses sum up to efficiency gains of 0.8%, 1.6%, and 1.3%, respectively, which is 3.7% in total. The efficiency gap between real and ideal solar cell is, however, much larger with 7.3%. The discrepancy is mainly due to the non-linear behaviour of recombination-based power losses which adds synergetic efficiency enhancements

Lightweight Multiplication in GF(2^n) with Applications to MDS Matrices

In this paper we consider the fundamental question of optimizing finite field multiplications with one fixed element. Surprisingly, this question did not receive much attention previously. We investigate which field representation, that is which choice of basis, allows for an optimal implementation. Here, the efficiency of the multiplication is measured in terms of the number of XOR operations needed to implement the multiplication. While our results are potentially of larger interest, we focus on a particular application in the second part of our paper. Here we construct new MDS matrices which outperform or are on par with all previous results when focusing on a round-based hardware implementation

Linear Cryptanalysis: Key Schedules and Tweakable Block Ciphers

This paper serves as a systematization of knowledge of linear cryptanalysis and provides novel insights in the areas of key schedule design and tweakable block ciphers. We examine in a step by step manner the linear hull theorem in a general and consistent setting. Based on this, we study the influence of the choice of the key scheduling on linear cryptanalysis, a – notoriously difficult – but important subject. Moreover, we investigate how tweakable block ciphers can be analyzed with respect to linear cryptanalysis, a topic that surprisingly has not been scrutinized until now

Decomposing the ASASA Block Cipher Construction

We consider the problem of recovering the internal specification of a general SP-network consisting of three linear layers (A) interleaved with two Sbox layers (S) (denoted by ASASA for short), given only black-box access to the scheme. The decomposition of such general ASASA schemes was first considered at ASIACRYPT 2014 by Biryukov et al. which used the alleged difficulty of this problem to propose several concrete block cipher designs as candidates for white-box cryptography. In this paper, we present several attacks on general ASASA schemes that significantly outperform the analysis of Biryukov et al. As a result, we are able to break all the proposed concrete ASASA constructions with practical complexity. For example, we can decompose an ASASA structure that was supposed to provide $64$-bit security in roughly $2^{28}$ steps, and break the scheme that supposedly provides $128$-bit security in about $2^{41}$ time. Whenever possible, our findings are backed up with experimental verifications

Shorter Linear Straight-Line Programs for MDS Matrices

Recently a lot of attention is paid to the search for efficiently implementable MDS matrices for lightweight symmetric primitives. Previous work concentrated on locally optimizing the multiplication with single matrix elements. Separate from this line of work, several heuristics were developed to find shortest linear straight-line programs. Solving this problem actually corresponds to globally optimizing multiplications by matrices. In this work we combine those, so far largely independent line of works. As a result, we achieve implementations of known, locally optimized, and new MDS matrices that significantly outperform all implementations from the literature. Interestingly, almost all previous locally optimized constructions behave very similar with respect to the globally optimized implementation. As a side effect, our work reveals the so far best implementation of the AES MixColumns operation with respect to the number of XOR operations needed

Wet chemical polishing for industrial type PERC solar cells

Industrial PERC cell process flows typically apply the polishing of the rear side after texturing as well as the edge isolation after POCl3 diffusion. In this paper, we present a novel single step polishing process which we apply post double sided texturing and diffusion in order to remove the rear emitter and to reduce the rear surface roughness. One challenge is to minimize the etch back of the front side emitter during rear side polishing due to the reactive gas phase of the polishing process. By optimizing the polishing process, we are able to limit the increase of the emitter sheet resistance below 5 Ω/sq. However, the wet cleaning post polishing contributes an additional 20 Ω/sq emitter sheet resistance increase which is subject to further optimization. We compensate the emitter sheet resistance increase due to wet cleaning by applying a 45 Ω/sq POCl3 diffusion instead of a 60 Ω/sq diffusion. The resulting PERC solar cells with polished rear surface post texture and diffusion show conversion efficiencies up to 19.6% which is comparable to the reference PERC cells which apply a rear protection layer instead of a polishing process.German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety/0325296Heraeus Precious MetalsRenaSingulus TechnologiesSolar Worl

Comparison of ICP-AlOx and ALD-Al2O3 layers for the rear surface passivation of c-Si solar cells

The deposition rate of the standard (i.e. sequential) atomic layer deposition (ALD) process is very low compared to the plasma-enhanced chemical vapour deposition (PECVD) process. Therefore, as a short- and medium-term perspective, PECVD aluminium oxide (AlOx) films might be better suited for the implementation into industrial-type solar cells than ALD-Al 2O3 films. In this paper, we report results achieved with a newly developed PECVD deposition process for AlOx using an inductively coupled plasma (ICP). We compare the results to high-quality ALDAl2O3 films. We examine a stack consisting of a thin AlOx passivation layer and a PECVD silicon nitride (SiNy) capping layer. Surface recombination velocities below 9 cm/s were measured on low-resistivity (1.4 Ωcm) p-type crystalline silicon wafers passivated either by ICP-PECVD-AlOx films or by ALD-Al2O3 films after annealing at 425°C. Both passivation schemes provide an excellent thermal stability during firing at 910°C with SRVs below 12 cm/s for both, Al2O3/SiNy stacks and single Al 2O3 layers. A fixed negative charge of -4×10 12 cm-2 is measured for ICP-AlOx and ALD-Al2O3, whereas the interface state density is higher for the ICP-AlOx layer with values of 11.0×1011 eV-1cm-2 compared to 1.3×1011 eV -1cm-2 for ALD-Al2O3. Implemented into large-area screen-printed PERC solar cells, an independently confirmed efficiency of 20.1% for ICP-AlOx and an efficiency of 19.6% for ALD-Al2O3 are achieved.BMU/0325296Solland Solar Cells BVSolarWorld Innovations GmbHSCHOTT Solar AGRENA GmbHSINGULUS TECHNOLOGIES A

Interaction of Water with Atomic Layer Deposited Titanium Dioxide on p‐Si Photocathode: Modeling of Photoelectrochemical Interfaces in Ultrahigh Vacuum with Cryo‐Photoelectron Spectroscopy

This study combines cryo‐photoelectron spectroscopy and electrochemical analysis techniques to investigate the p‐Si/SiO₂/TiO₂/H₂O system in the context of water‐splitting. Atomic layer deposition is used for the preparation of a TiO₂ thin film coating for a p‐Si/SiO₂ photocathode. First, an interface experiment is performed to study the contact properties of the interface between p‐Si/SiO₂ and TiO₂. For the p‐Si/TiO₂ heterojunction, a downward band bending of 0.3 eV is found for the p‐Si toward the interface. Second, a water adsorption experiment is conducted, which allows the investigation of the surface chemistry of the TiO₂ coating in contact to water. A direct correlation between the amount of surface hydroxide species, formed due to water dissociation, and Ti³⁺ defect state density is found. Furthermore, a surface water species can be identified in addition to the commonly found bulk molecular water. Together with the results from a Mott–Schottky analysis, a complete energy level alignment can be constructed

Literatur der Archäologie: Materialität und Rhetorik im 18. und 19. Jahrhundert

Seit der Einführung des Konzepts einer »Archäologie des Wissens« ist wiederholt versucht worden, den Begriff der Archäologie für eine allgemeine Kulturtheorie zu funktionalisieren. Umfangreich erschienen in der Folge die Archäologien, als deren Gegenstände nicht einmal mehr die Gegenwart oder die Zukunft undenkbar sind. Daneben musste sich, wie alle Kulturwissenschaften, das institutionelle Fach Archäologie mit dem prägenden Einfluss sprachlicher Bedingungen auf die Gewinnung von Erkenntnissen auseinandersetzen. Dies verweist auf eine zentrale Problematik, die eng an der Kombination von Archäologie und Germanistik in der konzeptionellen Gestaltung des Forschungskollegs Morphomata orientiert ist, nämlich das wechselseitige Verhältnis visuell wahrgenommener und literarisch vermittelter Form sowie ihre Bezüge zu einer ihnen zugrunde liegenden Vorstellung. Der vorliegende Sammelband will über Fallbeispiele aus den Blickwinkeln der Fachdisziplinen der Archäologie und der Literaturwissenschaften Veränderungen und Persistenzen in der Erschließung von Antike deutlich machen. Im Zentrum der Beiträge stehen erstens die Verwendung des Begriffs »Archäologie« außerhalb des aus heutiger Sicht dafür charakteristischen Feldes der Ausgrabung und deutenden Erfassung überlieferter materialer Fundstücke, zweitens die dichterische Darstellung archäologischer Tätigkeit im modernen Sinne der sich ausbildenden Fachdisziplin und drittens Literatur als Medium der Formulierung und Systematisierung generierter Wissensbestände bzw. intersubjektiver Diskursivität der Archäologie

Adenosine/A2B receptor signaling ameliorates the effects of ageing and counteracts obesity

The combination of aging populations with the obesity pandemic results in an alarming rise in non-communicable diseases. Here, we show that the enigmatic adenosine A2B receptor (A2B) is abundantly expressed in skeletal muscle (SKM) as well as brown adipose tissue (BAT) and might be targeted to counteract age-related muscle atrophy (sarcopenia) as well as obesity. Mice with SKM-specific deletion of A2B exhibited sarcopenia, diminished muscle strength, and reduced energy expenditure (EE), whereas pharmacological A2B activation counteracted these processes. Adipose tissue-specific ablation of A2B exacerbated age-related processes and reduced BAT EE, whereas A2B stimulation ameliorated obesity. In humans, A2B expression correlated with EE in SKM, BAT activity, and abundance of thermogenic adipocytes in white fat. Moreover, A2B agonist treatment increased EE from human adipocytes, myocytes, and muscle explants. Mechanistically, A2B forms heterodimers required for adenosine signaling. Overall, adenosine/A2B signaling links muscle and BAT and has both anti-aging and anti-obesity potential