Perovskite/Silicon Tandem Solar Cells: Toward Affordable Ultra-High Efficiency Photovoltaics ?

Nowadays the photovoltaics market is dominated by crystalline silicon solar cells, which are approaching their theoretical efficiency limit. Novel solutions have to be found for photovoltaics to further enhance its competitiveness with other energy sources. One of the most promising approaches lies in combining market-proven silicon solar cell technology, having a low optical band gap, with an efficient near-infrared transparent wide-band gap top cell to form a tandem cell. Organic-inorganic halide perovskite solar cells are promising candidates for top cells, showing high efficiencies with simple and cost-effective device fabrication. We first develop perovskite solar cells specifically for tandem applications. We develop and optimize a hybrid sequential deposition method combining thermal evaporation and solution processing to fabricate perovskite absorber materials with specifically tailored optoelectronic properties. These materials are systematically investigated for their optical, structural and electronic properties, and then applied in perovskite solar cells both in n-i-p and p-i-n configurations, for which we show several charge transport materials combinations. As a replacement for the standard metal opaque rear electrode of perovskite cells, we develop a TCO-based transparent electrode, for which sputtered IZO is presented as a good candidate thanks to its high carrier mobility and broadband transparency. Sputtering-induced damages are reduced by the introduction of a buffer layer: MoOx for n-i-p cells and SnO2 for p-i-n cells. The parasitic absorption losses in the MoOx are described in details. We then discuss the parasitic absorption losses in charge transport layers and TCOs, with experimental comparison of various materials. The optimisation of the perovskite absorber deposition method and the improvement of the charge transport layers and transparent electrode allows the fabrication 1cm2 area semitransparent perovskite solar cells with >16% efficiency. We then integrate the semitransparent perovskite cells in mechanically stacked 4-terminal tandem solar cells. The challenges in reducing the strong parasitic absorption and reflection losses are first discussed. We then demonstrate 4-terminal tandem measurements with >25% total efficiency with a small area top cell. With larger 1cm2 area top cells, we fabricate integrated 4-terminal tandem devices with both subcells having similar size and total efficiency >23%. The integration of perovskite solar cells in 2-terminal monolithically connected tandem solar cells with silicon heterojunction bottom cells is finally presented. First, we show the development of a TCO-based recombination layer and the important reflection losses and interference effects observed in all-flat devices. The origins of parasitic absorption losses in monolithic tandems are then explained and new architectures and materials are investigated supported by optical simulations. We then replace the polished wafers by fully textured silicon bottom cells for better light management. The development of a tandem device with the top cell conformally coated onto the textured bottom cell is explained, leading to >25% certified power conversion efficiency. The end of the thesis presents preliminary results on the up-scalability and light soaking stability of the developed textured tandems, as well as a proof-of-concept of a first perovskite/perovskite/silicon triple junction solar cell on textured wafers

Multimodal Microscale Imaging of Textured Perovskite-Silicon Tandem Solar Cells.

Halide perovskite/crystalline silicon (c-Si) tandem solar cells promise power conversion efficiencies beyond the limits of single-junction cells. However, the local light-matter interactions of the perovskite material embedded in this pyramidal multijunction configuration, and the effect on device performance, are not well understood. Here, we characterize the microscale optoelectronic properties of the perovskite semiconductor deposited on different c-Si texturing schemes. We find a strong spatial and spectral dependence of the photoluminescence (PL) on the geometrical surface constructs, which dominates the underlying grain-to-grain PL variation found in halide perovskite films. The PL response is dependent upon the texturing design, with larger pyramids inducing distinct PL spectra for valleys and pyramids, an effect which is mitigated with small pyramids. Further, optimized quasi-Fermi level splittings and PL quantum efficiencies occur when the c-Si large pyramids have had a secondary smoothing etch. Our results suggest that a holistic optimization of the texturing is required to maximize light in- and out-coupling of both absorber layers and there is a fine balance between the optimal geometrical configuration and optoelectronic performance that will guide future device designs

Efficient Near-Infrared-Transparent Perovskite Solar Cells Enabling Direct Comparison of 4-Terminal and Monolithic Perovskite/Silicon Tandem Cells

Combining market-proven silicon solar cell technology with an efficient wide band gap top cell into a tandem device is an attractive approach to reduce the cost of photovoltaic systems. For this, perovskite solar cells are promising high-efficiency top cell candidates, but their typical device size (<0.2 cm2), is still far from standard industrial sizes. We present a1cm2 near-infrared transparent perovskite solar cell with 14.5% steady- state efficiency, as compared to 16.4% on 0.25 cm2. By mechanically stacking these cells with silicon heterojunction cells, we experimentally demonstrate a 4-terminal tandem measurement with a steady-state efficiency of 25.2%, with a 0.25 cm2 top cell. The developed top cell processing methods enable the fabrication of a 20.5% efficient and 1.43 cm2 large monolithic perovskite/silicon heterojunction tandem solar cell, featuring a rear-side textured bottom cell to increase its near-infrared spectral response. Finally, we compare both tandem configurations to identify efficiency-limiting factors and discuss the potential for further performance improvement

Zinc tin oxide as high-temperature stable recombination layer for mesoscopic perovskite/silicon monolithic tandem solar cells

Perovskite/crystalline silicon tandem solar cells have the potential to reach efficiencies beyond those of silicon single-junction record devices. However, the high-temperature process of 500 °C needed for state-of-the-art mesoscopic perovskite cells has, so far, been limiting their implementation in monolithic tandem devices. Here, we demonstrate the applicability of zinc tin oxide as a recombination layer and show its electrical and optical stability at temperatures up to 500 °C. To prove the concept, we fabricate monolithic tandem cells with mesoscopic top cell with up to 16% efficiency. We then investigate the effect of zinc tin oxide layer thickness variation, showing a strong influence on the optical interference pattern within the tandem device. Finally, we discuss the perspective of mesoscopic perovskite cells for high-efficiency monolithic tandem solar cells

Fully textured monolithic perovskite/silicon tandem solar cells with 25.2% power conversion efficiency

Tandem devices combining perovskite and silicon solar cells are promising candidates to achieve power conversion efficiencies above 30% at reasonable costs. State-of-the-art monolithic two-terminal perovskite/silicon tandem devices have so far featured silicon bottom cells that are polished on their front side to be compatible with the perovskite fabrication process. This concession leads to higher potential production costs, higher reflection losses and non-ideal light trapping. To tackle this issue, we developed a top cell deposition process that achieves the conformal growth of multiple compounds with controlled optoelectronic properties directly on the micrometre-sized pyramids of textured monocrystalline silicon. Tandem devices featuring a silicon heterojunction cell and a nanocrystalline silicon recombination junction demonstrate a certified steady-state efficiency of 25.2%. Our optical design yields a current density of 19.5 mA cm−2 thanks to the silicon pyramidal texture and suggests a path for the realization of 30% monolithic

Wege in die Ernährungszukunft der Schweiz - Leitfaden zu den grössten Hebeln und politischen Pfaden für ein nachhaltiges Ernährungssystem

Aus wissenschaftlicher Sicht ist klar: Unser Ernährungssystem ist nicht nachhaltig. Um unsere Lebens- und Wirtschaftsgrundlagen zu erhalten, braucht es eine Neuausrichtung über die gesamte Wertschöpfungskette. Diese ist gleichzeitig ein Schlüssel zur Erreichung der Agenda 2030 für nachhaltige Entwicklung. SDSN Schweiz hat das wissenschaftliche Gremium Ernährungszukunft Schweiz initiiert, um einen Wegweiser zu entwickeln. Er soll es der Schweiz erlauben, Chancen rechtzeitig anzupacken und unkontrollierbare Kostenfolgen zu vermeiden. Das wissenschaftliche Gremium hat international wegweisende Pionierarbeit geleistet. In einem interdisziplinären wissenschaftlichen Prozess wurde zum ersten Mal für ein Land ein umfassender Handlungspfad zur Neuausrichtung des Ernährungssystems im Einklang mit den Zielen für nachhaltige Entwicklung ausgearbeitet. Die beteiligten Forschenden schaffen damit eine wichtige Grundlage für die weitere politische Diskussion in der Schweiz und international

Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan

This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good

Juxtaposing BTE and ATE – on the role of the European insurance industry in funding civil litigation

One of the ways in which legal services are financed, and indeed shaped, is through private insurance arrangement. Two contrasting types of legal expenses insurance contracts (LEI) seem to dominate in Europe: before the event (BTE) and after the event (ATE) legal expenses insurance. Notwithstanding institutional differences between different legal systems, BTE and ATE insurance arrangements may be instrumental if government policy is geared towards strengthening a market-oriented system of financing access to justice for individuals and business. At the same time, emphasizing the role of a private industry as a keeper of the gates to justice raises issues of accountability and transparency, not readily reconcilable with demands of competition. Moreover, multiple actors (clients, lawyers, courts, insurers) are involved, causing behavioural dynamics which are not easily predicted or influenced. Against this background, this paper looks into BTE and ATE arrangements by analysing the particularities of BTE and ATE arrangements currently available in some European jurisdictions and by painting a picture of their respective markets and legal contexts. This allows for some reflection on the performance of BTE and ATE providers as both financiers and keepers. Two issues emerge from the analysis that are worthy of some further reflection. Firstly, there is the problematic long-term sustainability of some ATE products. Secondly, the challenges faced by policymakers that would like to nudge consumers into voluntarily taking out BTE LEI

Search for stop and higgsino production using diphoton Higgs boson decays

Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top-quark (stop) and the Higgs boson (higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7 inverse femtobarns of proton-proton collision data at sqrt(s) = 8 TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the stop mass below 360 to 410 GeV, depending on the higgsino mass

Severe early onset preeclampsia: short and long term clinical, psychosocial and biochemical aspects

Preeclampsia is a pregnancy specific disorder commonly defined as de novo hypertension and proteinuria after 20 weeks gestational age. It occurs in approximately 3-5% of pregnancies and it is still a major cause of both foetal and maternal morbidity and mortality worldwide1. As extensive research has not yet elucidated the aetiology of preeclampsia, there are no rational preventive or therapeutic interventions available. The only rational treatment is delivery, which benefits the mother but is not in the interest of the foetus, if remote from term. Early onset preeclampsia (<32 weeks’ gestational age) occurs in less than 1% of pregnancies. It is, however often associated with maternal morbidity as the risk of progression to severe maternal disease is inversely related with gestational age at onset2. Resulting prematurity is therefore the main cause of neonatal mortality and morbidity in patients with severe preeclampsia3. Although the discussion is ongoing, perinatal survival is suggested to be increased in patients with preterm preeclampsia by expectant, non-interventional management. This temporising treatment option to lengthen pregnancy includes the use of antihypertensive medication to control hypertension, magnesium sulphate to prevent eclampsia and corticosteroids to enhance foetal lung maturity4. With optimal maternal haemodynamic status and reassuring foetal condition this results on average in an extension of 2 weeks. Prolongation of these pregnancies is a great challenge for clinicians to balance between potential maternal risks on one the eve hand and possible foetal benefits on the other. Clinical controversies regarding prolongation of preterm preeclamptic pregnancies still exist – also taking into account that preeclampsia is the leading cause of maternal mortality in the Netherlands5 - a debate which is even more pronounced in very preterm pregnancies with questionable foetal viability6-9. Do maternal risks of prolongation of these very early pregnancies outweigh the chances of neonatal survival? Counselling of women with very early onset preeclampsia not only comprises of knowledge of the outcome of those particular pregnancies, but also knowledge of outcomes of future pregnancies of these women is of major clinical importance. This thesis opens with a review of the literature on identifiable risk factors of preeclampsia