Charge transport properties of organic conjugated polymers for photovoltaic applications

Charge transport in conjugated polymers as well as in bulk-heterojunction (BHJ) solar cells made of blends between conjugated polymers, as electron-donors (D), and fullerenes, as electron-acceptors (A), has been investigated. It is shown how charge carrier mobility of a series of anthracene-containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene)s (AnE-PVs) is highly dependent on the lateral chain of the polymers, on a moderate variation of the macromolecular parameters (molecular weight and polydispersity), and on the processing conditions of the films. For the first time, the good ambipolar transport properties of this relevant class of conjugated polymers have been demonstrated, consistent with the high delocalization of both the frontier molecular orbitals. Charge transport is one of the key parameters in the operation of BHJ solar cells and depends both on charge carrier mobility in pristine materials and on the nanoscale morphology of the D/A blend, as proved by the results here reported. A straight correlation between hole mobility in pristine AnE-PVs and the fill factor of the related solar cells has been found. The great impact of charge transport for the performance of BHJ solar cells is clearly demonstrated by the results obtained on BHJ solar cells made of neat-C70, instead of the common soluble fullerene derivatives (PCBM or PC70BM). The investigation of neat-C70 solar cells was motivated by the extremely low cost of non-functionalized fullerenes, compared with that of their soluble derivatives (about one-tenth). For these cells, an improper morphology of the blend leads to a deterioration of charge carrier mobility, which, in turn, increases charge carrier recombination. Thanks to the appropriate choice of the donor component, solar cells made of neat-C70 exhibiting an efficiency of 4.22% have been realized, with an efficiency loss of just 12% with respect to the counterpart made with costly PC70BM.

Traditional risk factors and lifetime risk of acute coronary events

Objective: To investigate the association between the four traditional coronary heart disease (CHD) risk factors (hypertension, smoking, hypercholesterolemia, and diabetes) and outcomes of first ACS. Methods: Data were drawn from the ISACS Archives. The study participants consisted of 70953 patients with first ACS, but without prior CHD. Primary outcomes were patient’ age at hospital presentation and 30-day all-cause mortality. The risk ratios for mortality among subgroups were calculated using a balancing strategy by inverse probability weighting. Trends were evaluated by Pearson's correlation coefficient (r). Results: For fatal ACS (n=6097), exposure to at least one traditional CHD-risk factor ranged from 77.6% in women to 74.5% in men. The presence of all four CHD-risk factors significantly decreased the age at time of ACS event and death by nearly half a decade compared with the absence of any traditional risk factors in both women (from 67.1±12.0 to 61.9±10.3 years; r=-0.089, P<0.001) and men (from 62.8±12.2 to 58.9±9.9 years; r=-0.096, P<0.001). By contrast, there was an inverse association between the number of traditional CHD-risk factors and 30-day mortality. The mortality rates in women ranged from 7.7% with four traditional CHD-risk factors to 16.3% with no traditional risk factors (r=0.073, P<0.001). The corresponding rates in men were 4.8% and 11.5% (r=0.078, P<0.001), respectively. The risk ratios among individuals with at least one CHD-risk factors vs. those with no traditional risk factors were 0.72 (95%CI:0.65-0.79) in women and 0.64 (95%CI:0.59-0.70) in men. This association was consistent among patient subgroups managed with guideline-recommended therapeutic options. Conclusions: The vast majority of patients who die for ACS have traditional CHD-risk factor exposure. Patients with CHD-risk factors die much earlier in life, but they have a lower relative risk of 30-day mortality than those with no traditional CHD-risk factors, even in the context of equitable evidence‐based treatments after hospital admission.