Improving Monolithic Perovskite Silicon Tandem Solar Cells From an Optical Viewpoint

Perovskite silicon tandem solar cells are the most promising concept for a future photovoltaic technology. We report on recent progress from an optical viewpoint and disucss how we achieved more than 25 device efficienc

Autonomous QoS Management and Policing in Unmanaged Local Area Networks

The high increase of bandwidth-intensive applications like high definition video streaming in home and small office environments leads to QoS challenges in hybrid wired/wireless local area networks. These networks are often not QoS aware and may contain bottlenecks in their topology. In addition, they often have a hybrid nature due to the used access technology consisting of, for example, Ethernet, wireless, and PowerLAN links. In this paper, we present the research work on a novel autonomous system for hybrid QoS in local area networks, called QoSiLAN, which does not rely on network infrastructure support but on host cooperation and works independently of the access technology. We present a new QoS Signalling Protocol, policing and admission control algorithms, and a new lightweight statistical bandwidth prediction algorithm for autonomous resource management in LANs. This new QoS framework enables link based, access-medium independent bandwidth management without network support. We provide evaluation results for the novel bandwidth prediction algorithm as well as for the QoSiLAN framework and its protocol, which highlight the features, robustness, and the effectiveness of the proposed system

To be or not to be the odd one out - Allele-specific transcription in pentaploid dogroses (Rosa L. sect. Caninae (DC.) Ser)

<p>Abstract</p> <p>Background</p> <p>Multiple hybridization events gave rise to pentaploid dogroses which can reproduce sexually despite their uneven ploidy level by the unique canina meiosis. Two homologous chromosome sets are involved in bivalent formation and are transmitted by the haploid pollen grains and the tetraploid egg cells. In addition the egg cells contain three sets of univalent chromosomes which are excluded from recombination. In this study we investigated whether differential behavior of chromosomes as bivalents or univalents is reflected by sequence divergence or transcription intensity between homeologous alleles of two single copy genes (<it>LEAFY</it>, <it>cGAPDH</it>) and one ribosomal DNA locus (<it>nrITS</it>).</p> <p>Results</p> <p>We detected a maximum number of four different alleles of all investigated loci in pentaploid dogroses and identified the respective allele with two copies, which is presumably located on bivalent forming chromosomes. For the alleles of the ribosomal DNA locus and <it>cGAPDH </it>only slight, if any, differential transcription was determined, whereas the <it>LEAFY </it>alleles with one copy were found to be significantly stronger expressed than the <it>LEAFY </it>allele with two copies. Moreover, we found for the three marker genes that all alleles have been under similar regimes of purifying selection.</p> <p>Conclusions</p> <p>Analyses of both molecular sequence evolution and expression patterns did not support the hypothesis that unique alleles probably located on non-recombining chromosomes are less functional than duplicate alleles presumably located on recombining chromosomes.</p

27.9 Efficient Monolithic Perovskite Silicon Tandem Solar Cells on Industry Compatible Bottom Cells

Monolithic perovskite silicon tandem solar cells recently surpass the efficiency of silicon single junction solar cells. Most tandem cells utilize gt;250 amp; 8201; amp; 956;m thick, planarized float zone FZ silicon, which is not compatible with commercial production using lt;200 amp; 8201; amp; 956;m thick Czochralski CZ silicon. The perovskite silicon tandem cells based on industrially relevant 100 amp; 8201; amp; 956;m thick CZ silicon without mechanical planarization are demonstrated. The best power conversion efficiency PCE of 27.9 is only marginally below the 28.2 reference value obtained on the commonly used front side polished FZ Si, which are about three times thicker. With both wafer types showing the same median PCE of 27.8 , the thin CZ Si based devices are preferred for economic reasons. To investigate perspectives for improved current matching and, therefore, further efficiency improvement, optical simulations with planar and textured silicon have been conducted the perovskite s bandgap needs to be increased by amp; 8776;0.02 amp; 8201;eV when reducing the silicon thickness from 280 to 100 amp; 8201; amp; 956;m. The need for bandgap enlargement has a strong impact on future tandem developments ensuring photostable compositions with lossless interfaces at bandgaps around or above 1.7 amp; 8201;e

Perovskite CIGS Tandem Solar Cells From Certified 24.2 toward 30 and Beyond

We demonstrate a monolithic perovskite CIGS tandem solar cell with a certified power conversion efficiency PCE of 24.2 . The tandem solar cell still exhibits photocurrent mismatch between the subcells; thus optical simulations are used to determine the optimal device stack. Results reveal a high optical potential with the optimized device reaching a short circuit current density of 19.9 mA cm 2 and 32 PCE based on semiempirical material properties. To evaluate its energy yield, we first determine the CIGS temperature coefficient, which is at amp; 8722;0.38 K 1 notably higher than the one from the perovskite subcell amp; 8722;0.22 K 1 , favoring perovskite in the field operation at elevated cell temperatures. Both single junction cells, however, are significantly outperformed by the combined tandem device. The enhancement in energy output is more than 50 in the case of CIGS single junction device. The results demonstrate the high potential of perovskite CIGS tandem solar cells, for which we describe optical guidelines toward 30 PC

Proton Radiation Hardness of Perovskite Tandem Photovoltaics.

Monolithic [Cs0.05(MA0. 17FA0. 83)0.95]Pb(I0.83Br0.17)3/Cu(In,Ga)Se2 (perovskite/CIGS) tandem solar cells promise high performance and can be processed on flexible substrates, enabling cost-efficient and ultra-lightweight space photovoltaics with power-to-weight and power-to-cost ratios surpassing those of state-of-the-art III-V semiconductor-based multijunctions. However, to become a viable space technology, the full tandem stack must withstand the harsh radiation environments in space. Here, we design tailored operando and ex situ measurements to show that perovskite/CIGS cells retain over 85% of their initial efficiency even after 68 MeV proton irradiation at a dose of 2 × 1012 p+/cm2. We use photoluminescence microscopy to show that the local quasi-Fermi-level splitting of the perovskite top cell is unaffected. We identify that the efficiency losses arise primarily from increased recombination in the CIGS bottom cell and the nickel-oxide-based recombination contact. These results are corroborated by measurements of monolithic perovskite/silicon-heterojunction cells, which severely degrade to 1% of their initial efficiency due to radiation-induced recombination centers in silicon.F.L. acknowledges financial support from the Alexander von Humboldt Foundation via the Feodor Lynen program and thanks Prof. Sir R. Friend for supporting his Fellowship at the Cavendish Laboratory. This work was supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (HYPERION, grant agreement number 756962). M.J, A.A.A., E.K., and S.A. acknowledge financial support from the German Federal Ministry of Education and Research (BMBF) via program “Materialforschung für die Energiewende” (grant no. 03SF0540), by the German Federal Ministry for Economic Affairs and Energy (BMWi) through the ‘PersiST’ project (Grant No. 0324037C). T.B. C.A.K. and R.S. acknowledge funding by BMWi through the speedCIGS (grant no. 0324095E) and EFFCIS project (grant no. 0324076D). D.K. and M.C. acknowledge financial support from the Dutch Ministry of Economic Affairs, via The Top-consortia Knowledge and Innovation (TKI) Program ‘‘Photovoltaic modules based on a p-i-n stack, manufactured on a roll-to-roll line featuring high efficiency, stability and strong market perspective’’ (PVPRESS) (TEUE118010) and “Bridging the voltage gap” (BRIGHT) (1721101). K. F. acknowledges the George and Lilian Schiff Fund, the Engineering and Physical Sciences Research Council (EPSRC), the Winton Sustainability Fellowship, and the Cambridge Trust for funding. S.D.S. acknowledges the Royal Society and Tata Group (UF150033). The authors acknowledge the EPSRC for funding (EP/R023980/1). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 841265. A.R.B. acknowledges funding from a Winton Studentship, Oppenheimer Studentship, and funding from the Engineering and Physical Sciences Research Council (EPSRC) Doctoral Training Centre in Photovoltaics (CDT-PV). K.G. acknowledges the Polish Ministry of Science and Higher Education within the Mobilnosc Plus program (Grant No. 1603/MOB/V/2017/0)

Textured interfaces in monolithic perovskite silicon tandem solar cells advanced light management for improved efficiency and energy yield

Efficient light management in monolithic perovskite silicon tandem solar cells is one of the prerequisites for achieving high power conversion efficiencies PCEs . Textured silicon wafers can be utilized for light management, however, this is typically not compatible with perovskite solution processing. Here, we instead employ a textured light management LM foil on the front side of a tandem solar cell processed on a wafer with planar front side and textured back side. This way the PCE of monolithic, 2 terminal perovskite silicon heterojunction tandem solar cells is significantly improved from 23.4 to 25.5 . Furthermore, we validate an advanced numerical model for our fabricated device and use it to optically optimize a number of device designs with textures at different interface with respect to the PCE and energy yield. These simulations predict a slightly lower optimal bandgap of the perovskite top cell in a textured device as compared to a flat one and demonstrate strong interdependency between the bandgap and the texture position in the monolithic stack. We estimate the PCE potential for the best performing both side textured device to be 32.5 for a perovskite bandgap of 1.66 eV. Furthermore, the results show that under perpendicular illumination conditions, for optimized designs, the LM foil on top of the cell performs only slightly better than a flat anti reflective coating. However, under diffuse illumination, the benefits of the LM foil are much greater. Finally, we calculate the energy yield for the different device designs, based on true weather data for three different locations throughout the year, taking direct as well as diffuse illumination fully into account. The results further confirm the benefits of front side texture, even more for BIPV applications. Overall, devices built on a both side textured silicon wafer perform best. However, we show that devices with textured LM foils on the cell s front side are a highly efficient alternativ

21.6 efficient Monolithic Perovskite Cu In,Ga Se2 Tandem Solar Cells with Thin Conformal Hole Transport Layers for Integration on Rough Bottom Cell Surfaces

Perovskite based tandem solar cells can increase the power conversion efficiency PCE of conventional single junction photovoltaic devices. Here, we present monolithic perovskite CIGSe tandem solar cells with a perovskite top cell fabricated directly on an as grown, rough CIGSe bottom cell. To prevent potential shunting due to the rough CIGSe surface, a thin NiOx layer is conformally deposited via atomic layer deposition on the front contact of the CIGSe bottom cell. The performance is further improved by an additional layer of the polymer PTAA at the NiOx perovskite interface. This hole transport bilayer enables a 21.6 stabilized PCE of the tandem device at amp; 8764;0.8 cm2 active area. We use TEM EDX measurements to investigate the deposition uniformity and conformality of the NiOx and PTAA layers. By absolute photoluminescence measurements, the contribution of the individual subcells to the tandem VOC is determined, revealing that further fine tuning of the recombination layers might improve the tandem VOC. Finally, on the basis of the obtained results, we give guidelines to improve monolithic perovskite CIGSe tandems toward predicted PCE estimates above 3

Determining Structure Activity Relationships in Oxide Derived Cu Sn Catalysts During CO2 Electroreduction Using X Ray Spectroscopy

The development of earth abundant catalysts for selective electrochemical CO2 conversion is a central challenge. Cu amp; 63743;Sn bimetallic catalysts can yield selective CO2 reduction toward either CO or formate. This study presents oxide derived Cu amp; 63743;Sn catalysts tunable for either product and seeks to understand the synergetic effects between Cu and Sn causing these selectivity trends. The materials undergo significant transformations under CO2 reduction conditions, and their dynamic bulk and surface structures are revealed by correlating observations from multiple methods X ray absorption spectroscopy for in situ study, and quasi in situ X ray photoelectron spectroscopy for surface sensitivity. For both types of catalysts, Cu transforms to metallic Cu0 under reaction conditions. However, the Sn speciation and content differ significantly between the catalyst types the CO selective catalysts exhibit a surface Sn content of 13 at. predominantly present as oxidized Sn, while the formate selective catalysts display an Sn content of amp; 8776;70 at. consisting of both metallic Sn0 and Sn oxide species. Density functional theory simulations suggest that Sn amp; 948; sites weaken CO adsorption, thereby enhancing CO selectivity, while Sn0 sites hinder H adsorption and promote formate production. This study reveals the complex dependence of catalyst structure, composition, and speciation with electrochemical bias in bimetallic Cu catalyst

Subcell Operation and Long Term Stability Analysis of Perovskite Based Tandem Solar Cells Using a Bichromatic Light Emitting Diode Light Source

In monolithic tandem solar cells, current voltage J V characteristics of subcells provide invaluable information about their quality and tandem operation. However, accessing the subcell J Vs is challenging and requires sophisticated spectral methods. Herein, a customized, bichromatic light emitting diode setup BCLED for in depth analysis of tandem solar cells, suitable for subcell operation analysis, and long term stability testing is presented. For this, two spectrally independent LED arrays are used to selectively bias the two subcells. The power of the developed setup is demonstrated by successfully disentangling the tandem J V curve into subcell J V curves. The method is based on a one diode model for each subcell and is validated by electrical simulations. Afterward, it is used on a fabricated 27.6 efficient perovskite silicon tandem device, resulting in great agreement with the measured J V curve. Therefore, the BCLED setup is a versatile tool, suitable for subcell characteristics and long term stability analysis of tandem solar cell