Perovskite Solar Cells with Large Area CVD Graphene for Tandem Solar Cells

Perovskite solar cells with transparent contacts may be used to compensate for thermalization losses of silicon solar cells in tandem devices. This offers a way to outreach stagnating efficiencies. However, perovskite top cells in tandem structures require contact layers with high electrical conductivity and optimal transparency. We address this challenge by implementing large area graphene grown by chemical vapor deposition as a highly transparent electrode in perovskite solar cells, leading to identical charge collection efficiencies. Electrical performance of solar cells with a graphene based contact reached those of solar cells with standard gold contacts. The optical transmission by far exceeds that of reference devices and amounts to 64.3 below the perovskite band gap. Finally, we demonstrate a four terminal tandem device combining a high band gap graphene contacted perovskite top solar cell Eg 1.6 eV with an amorphous crystalline silicon bottom solar cell Eg 1.12 e

The potential role of mitochondrial ATP synthase inhibitory factor 1 (IF1) in coronary heart disease: a literature review

Cardiovascular disease (CVD) is the leading cause of death worldwide, and so the search for innovative and accurate biomarkers for guiding prevention, diagnosis, and treatment is a valuable clinical and economic endeavor. Due to a recent findings that the serum concentration of mitochondrial ATP synthase inhibitory factor 1 (IF1) is an independent prognostic factor in patients with coronary heart disease (CHD), we reviewed the role of this protein in myocardial ischemic preconditioning, its correlation to plasma high density lipoprotein (HDL), the predictive potential in patients with CHD, and its interplay with angiogenesis. IF1 has been positively correlated with plasma HDL-cholesterol, and is independently negatively associated with all-cause and CV mortality in patients with CHD. However, this conclusion is prevalently based on limited data, and more research is needed to draw definitive conclusions. IF1 seems to play an additional role in increasing cell vulnerability in oncologic diseases but may also function as modest inhibitor of angiogenesis in physiological conditions. It has been also explored that IF1 may rather act as a modulator of other molecules more significantly involved in angiogenesis, especially apolipoprotein A1 on which the largest effect could be observed. In conclusion, more research is needed to characterize the role of IF1 in patients with CHD

In situ graphene doping as a route toward efficient perovskite tandem solar cells

Tandem solar cells consisting of perovskite and silicon absorbers have the potential to outperform respective state of the art single junction efficiencies. However, their development requires the gentle deposition of a transparent electrode onto the hybrid perovskite and its organic layers. Implementation of large area graphene obtained by chemical vapor deposition seems to be an excellent solution. In this paper, we present the impact of graphene on perovskite solar cells and their organic layers. Direct application of graphene on CH3NH3PbI3 is limited by a highly defective interface but insertion of spiro OMeTAD enables a defect free implementation. Solar cells containing transparent graphene contacts approach identical electrical performance compared to devices with standard Au contacts. Hall effect measurements of graphene on various organic thin films, revealed the importance of field effect doping. Gained knowledge enabled the development of a strategy to increase the charge carrier density in graphene by 60 , while lowering graphene sheet resistance by 24 . This combined route of spiro OMeTAD and stabilized adsorbent doping is an important step toward the targeted application in high performance monolithic perovskite silicon tandem solar cell

Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn) As epitaxial layers

The effect of outdiffusion of Mn interstitials from (Ga,Mn) As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn) As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn) As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn) As, in agreement with the Zener model for ferromagnetic semiconductors. (C) 2014 AIP Publishing LLC