Equivalent Circuit Modeling for a High-Performance Large-Area Organic Photovoltaic Module

International audienceFor organic photovoltaics (OPVs) to contribute significantly to energy generation, they need to be scaled to large areas, much like all organic electronics. Therefore, there is a need for the development of a specific model that describes the electrical properties related to the size effects and cell interconnections. We report here on the equivalent circuit models for a high-performance series-connected OPV module based on a polymer:fullerene bulkheterojunction formulation. We examine the validity of the effective single cell methodology in the conventional framework and suggest a modified model that includes the net series resistance and additional parasitic leakage conductions. The photocurrent is found to follow the diffusion-limited voltage dependence, for which an empirical treatment enables an improved reproduction of the measurement near the short-circuit point

Solution processed reduced graphene oxide/metal oxide hybrid electron transport layers for highly efficient polymer solar cells

We report new solution processable electron transport layers for organic photovoltaic devices based on composites of metal oxides and reduced graphene oxides. Low bandgap polymer cells fabricated using these nanohybrid transport layers display power conversion efficiencies in the range of 7.4–7.5% which is observed to be an improvement over conventional metal oxide or thermally evaporated electron transport layers. This efficiency enhancement is driven mainly by improvements in the short circuit current (from ∼14.8 to ∼15.0 mA cm−2) as well as the fill factor (∼65% to ∼68%) upon the inclusion of reduced graphene oxide with the metal oxides. This is attributed to the reduced graphene oxide providing charge transfer pathways between the metal oxide nanoparticles. In addition, the metal oxide/reduced graphene oxide nanohybrids also lead to more balanced electron and hole mobilities which assist in the improvement of the fill factor of the device. The versatile nature of these nanohybrids is increased due to the wrapping of the graphene layers around the metal oxide nanoparticles, which leads to very smooth films with surface roughness of ∼3 nm. The improvement observed in this study upon the incorporation of RGO as well as the solution processable nature of the interfacial layers brings the organic photovoltaic technology a step closer towards realising an all solution processed solar cell

A critical look at organic photovoltaic fabrication methodology : defining performance enhancement parameters relative to active area

With the ever-increasing focus on obtaining higher device power conversion efficiencies (PCEs) for organic photovoltaics (OPV), there is a need to ensure samples are measured accurately. Reproducible results are required to compare data across different research institutions and countries and translate these improvements to real-world production. In order to report accurate results, and additionally find the best-practice methodology for obtaining and reporting these, we show that careful analysis of large data sets can identify the best fabrication methodology. We demonstrate which OPV outputs are most affected by different fabrication or measurement methods, and identify that masking effects can result in artificially-boosted PCEs by increasing fill factor and current densities, requiring care when selecting which mask to use. For example, our best performing devices (>6% efficiency) show that the smallest mask areas have not produced a surfeit of the highest performers, with only 11% of the top performing devices measured using a 0.032 cm2 mask area, while 44% used the largest mask (0.64 cm2). This trend holds true for efficiencies going down to 5%, showing that effective fabrication conditions are reproducible with increasing mask areas, and can be translated to even larger device areas. Finally, we emphasise the necessity for reporting the best PCE along with the average value in order to implement changes in real-world production

A Critical look at Organic Photovoltaic Fabrication Methodology: Defining performance enhancement parameters relative to active area

Abstract: With the ever-increasing focus on obtaining higher device power conversion efficiencies (PCEs) for organic photovoltaics (OPV), there is a need to ensure samples are measured accurately. Reproducible results are required to compare data across different research institutions and countries and translate these improvements to real-world production. In order to report accurate results, and additionally find the best-practice methodology for obtaining and reporting these, we show that careful analysis of large data sets can identify the best fabrication methodology. Furthermore, we demonstrate which OPV outputs are most affected with different fabrication or measurement methods. We also identify that masking effects can result in artificially-boosted PCEs by increasing fill factor and current densities, making a minimal mask size a requirement for accurate results. We illustrate the necessity for reporting the best PCE along with the average value in order to implement changes in real-world production

Rationale, design, and baseline characteristics in Evaluation of LIXisenatide in Acute Coronary Syndrome, a long-term cardiovascular end point trial of lixisenatide versus placebo

BACKGROUND: Cardiovascular (CV) disease is the leading cause of morbidity and mortality in patients with type 2 diabetes mellitus (T2DM). Furthermore, patients with T2DM and acute coronary syndrome (ACS) have a particularly high risk of CV events. The glucagon-like peptide 1 receptor agonist, lixisenatide, improves glycemia, but its effects on CV events have not been thoroughly evaluated. METHODS: ELIXA (www.clinicaltrials.gov no. NCT01147250) is a randomized, double-blind, placebo-controlled, parallel-group, multicenter study of lixisenatide in patients with T2DM and a recent ACS event. The primary aim is to evaluate the effects of lixisenatide on CV morbidity and mortality in a population at high CV risk. The primary efficacy end point is a composite of time to CV death, nonfatal myocardial infarction, nonfatal stroke, or hospitalization for unstable angina. Data are systematically collected for safety outcomes, including hypoglycemia, pancreatitis, and malignancy. RESULTS: Enrollment began in July 2010 and ended in August 2013; 6,068 patients from 49 countries were randomized. Of these, 69% are men and 75% are white; at baseline, the mean ± SD age was 60.3 ± 9.7 years, body mass index was 30.2 ± 5.7 kg/m(2), and duration of T2DM was 9.3 ± 8.2 years. The qualifying ACS was a myocardial infarction in 83% and unstable angina in 17%. The study will continue until the positive adjudication of the protocol-specified number of primary CV events. CONCLUSION: ELIXA will be the first trial to report the safety and efficacy of a glucagon-like peptide 1 receptor agonist in people with T2DM and high CV event risk