ABSTRACT
The short exciton diffusion length in organic semiconductors results in a strong dependence of the conversion efficiency of organic photovoltaic (OPV) cells on the morphology of the donor-acceptor bulk-heterojunction blend. Strong light-matter coupling provides a way to circumvent this dependence by combining the favorable properties of light and matter via the formation of hybrid exciton-polaritons. By strongly coupling excitons in P3HT-C60 OPV cells to Fabry-Perot optical cavity modes, exciton-polaritons are formed with increased propagation lengths. We exploit these exciton-polaritons to enhance the internal quantum efficiency of the cells, determined from the external quantum efficiency and the absorptance. Additionally, we find a consistent decrease in the Urbach energy for the strongly coupled cells, which indicates the reduction of energetic disorder due to the delocalization of exciton-polaritons in the optical cavity.
ABSTRACT
The rise in the power conversion efficiency (PCE) of perovskite solar cells has triggered enormous interest in perovskite-based tandem photovoltaics. One key challenge is to achieve high transmission of low energy photons into the bottom cell. Here, nanostructured front electrodes for 4-terminal perovskite/crystalline-silicon (perovskite/c-Si) tandem solar cells are developed by conformal deposition of indium tin oxide (ITO) on self-assembled polystyrene nanopillars. The nanostructured ITO is optimized for reduced reflection and increased transmission with a tradeoff in increased sheet resistance. In the optimum case, the nanostructured ITO electrodes enhance the transmittance by â¼7% (relative) compared to planar references. Perovskite/c-Si tandem devices with nanostructured ITO exhibit enhanced short-circuit current density (2.9â mA/cm2 absolute) and PCE (1.7% absolute) in the bottom c-Si solar cell compared to the reference. The improved light in-coupling is more pronounced for elevated angle of incidence. Energy yield enhancement up to â¼10% (relative) is achieved for perovskite/c-Si tandem architecture with the nanostructured ITO electrodes. It is also shown that these nanostructured ITO electrodes are also compatible with various other perovskite-based tandem architectures and bear the potential to improve the PCE up to 27.0%.
ABSTRACT
PURPOSE: Intensive care unit performance evaluation is usually affected by variations in the severity of inpatients' health status. This paper aims, therefore, to standardize two performance measures: intensive care unit survival and length of stay using the Acute Physiology and Chronic Health Evaluation II (APACHE II) severity of illness score. DESIGN/METHODOLOGY/APPROACH: A records study in three Ain Shams University Hospital intensive care units, from January 1-December 31, 2003 was carried out to examine illness severity effect using APACHE II, length of stay and survival. Retrospective data were used to model length of stay in days and the survival using the APACHE II score as a predictor. This was followed by a prospective study to monitor the standardized measures in two intensive care units for one year. FINDINGS: APACHE II scores predicted length of stay of those who were discharged and control charts for severity-adjusted length of stay were drawn up. The APACHE II score predicted survival for those with APACHE II score >16. The model is significant with a specificity of 89.9 percent while sensitivity was 25 percent. Control charts for severity-adjusted mortality were drawn up to monitor mortality. RESEARCH LIMITATIONS/IMPLICATIONS: Only 60 percent of the files examined in the retrospective part of the study had enough data to calculate APACHE II scores. PRACTICAL IMPLICATIONS: Standardized APACHE II severity of illness score can monitor intensive care unit length of stay and mortality. ORIGINALITY/VALUE: The paper underlines the need to implement a standardized measurement system to evaluate intensive care patient outcomes.
