Spectral Dependence of the Internal Quantum Efficiency of Organic Solar Cells: Effect of Charge Generation Pathways

The conventional picture of photocurrent generation in organic solar cells involves photoexcitation of the electron donor, followed by electron transfer to the acceptor via an interfacial charge-transfer state (Channel I). It has been shown that the mirror-image process of acceptor photoexcitation leading to hole transfer to the donor is also an efficient means to generate photocurrent (Channel II). The donor and acceptor components may have overlapping or distinct absorption characteristics. Hence, different excitation wavelengths may preferentially activate one channel or the other, or indeed both. As such, the internal quantum efficiency (IQE) of the solar cell may likewise depend on the excitation wavelength. We show that several model high-efficiency organic solar cell blends, notably PCDTBT:PC70BM and PCPDTBT:PC60/70BM, exhibit flat IQEs across the visible spectrum, suggesting that charge generation is occurring either via a dominant single channel or via both channels but with comparable efficiencies. In contrast, blends of the narrow optical gap copolymer DPP-DTT with PC70BM show two distinct spectrally flat regions in their IQEs, consistent with the two channels operating at different efficiencies. The observed energy dependence of the IQE can be successfully modeled as two parallel photodiodes, each with its own energetics and exciton dynamics but both having the same extraction efficiency. Hence, an excitation-energy dependence of the IQE in this case can be explained as the interplay between two photocurrent-generating channels, without recourse to hot excitons or other exotic processes

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is characterized by the development of many tens to thousands of adenomas in the rectum and colon during the second decade of life. FAP has an incidence at birth of about 1/8,300, it manifests equally in both sexes, and accounts for less than 1% of colorectal cancer (CRC) cases. In the European Union, prevalence has been estimated at 1/11,300-37,600. Most patients are asymptomatic for years until the adenomas are large and numerous, and cause rectal bleeding or even anemia, or cancer develops. Generally, cancers start to develop a decade after the appearance of the polyps. Nonspecific symptoms may include constipation or diarrhea, abdominal pain, palpable abdominal masses and weight loss. FAP may present with some extraintestinal manifestations such as osteomas, dental abnormalities (unerupted teeth, congenital absence of one or more teeth, supernumerary teeth, dentigerous cysts and odontomas), congenital hypertrophy of the retinal pigment epithelium (CHRPE), desmoid tumors, and extracolonic cancers (thyroid, liver, bile ducts and central nervous system). A less aggressive variant of FAP, attenuated FAP (AFAP), is characterized by fewer colorectal adenomatous polyps (usually 10 to 100), later age of adenoma appearance and a lower cancer risk. Some lesions (skull and mandible osteomas, dental abnormalities, and fibromas on the scalp, shoulders, arms and back) are indicative of the Gardner variant of FAP. Classic FAP is inherited in an autosomal dominant manner and results from a germline mutation in the adenomatous polyposis (APC) gene. Most patients (~70%) have a family history of colorectal polyps and cancer. In a subset of individuals, a MUTYH mutation causes a recessively inherited polyposis condition, MUTYH-associated polyposis (MAP), which is characterized by a slightly increased risk of developing CRC and polyps/adenomas in both the upper and lower gastrointestinal tract. Diagnosis is based on a suggestive family history, clinical findings, and large bowel endoscopy or full colonoscopy. Whenever possible, the clinical diagnosis should be confirmed by genetic testing. When the APC mutation in the family has been identified, genetic testing of all first-degree relatives should be performed. Presymptomatic and prenatal (amniocentesis and chorionic villous sampling), and even preimplantation genetic testing is possible. Referral to a geneticist or genetic counselor is mandatory. Differential diagnoses include other disorders causing multiple polyps (such as Peutz-Jeghers syndrome, familial juvenile polyps or hyperplastic polyposis, hereditary mixed polyposis syndromes, and Lynch syndrome). Cancer prevention and maintaining a good quality of life are the main goals of management and regular and systematic follow-up and supportive care should be offered to all patients. By the late teens or early twenties, colorectal cancer prophylactic surgery is advocated. The recommended alternatives are total proctocolectomy and ileoanal pouch or ileorectal anastomosis for AFAP. Duodenal cancer and desmoids are the two main causes of mortality after total colectomy, they need to be identified early and treated. Upper endoscopy is necessary for surveillance to reduce the risk of ampullary and duodenal cancer. Patients with progressive tumors and unresectable disease may respond or stabilize with a combination of cytotoxic chemotherapy and surgery (when possible to perform). Adjunctive therapy with celecoxib has been approved by the US Food and Drug Administration and the European Medicines Agency in patients with FAP. Individuals with FAP carry a 100% risk of CRC; however, this risk is reduced significantly when patients enter a screening-treatment program

Porphyrin-oligothiophene conjugates as additives for P3HT/PCBM solar cells

The power conversion efficiency (PCE) of poly(3-hexylthiophene)/fullerene (P3HT/PCBM) bulk heterojunction solar cells is enhanced through the addition of Ni(II) porphyrin-oligothiophene conjugates to typical P3HT/PCBM blends. The introduction of the porphyrin dyes increases the efficiency by up to 63 +/- 20% compared with P3HT/PCBM control devices containing no additives. Moreover, external quantum efficiency (EQE) measurements show a 10 +/- 5% enhancement in photocurrent compared to control blends. These results lead us to conclude that the photo-induced dissociation of P3HT excitons is promoted in the presence of the Ni(II) porphyrin-oligothiophenes and that the Ni(II) porphyrin subunits act as light-harvesting sensitizers as well as energy conduits for the P3HT excitons at P3HT/PCBM interfaces

Improving efficiencies by modulating the central metal ion in porphyrin-oligothiophene-mediated P3HT/PCBM organic solar cells

The power conversion efficiencies of poly(3-hexylthiophene)/[6,6]-phenyl-C-61-butyric acid methyl ester (P3HT/PCBM) bulk heterojunction organic solar cells were increased through the addition of small amounts (1-10%) of metalloporphyrin-oligothiophene conjugates. The effectiveness of these porphyrin additives was found to increase in the order free-base < Co < Zn < Ni < Cu, with the efficiency being enhanced by up to 17% for the terthiophene-substituted Cu(II)-porphyrin, pointing to an important effect of the metal center

Inhibition of the cellular function of perforin by 1-amino-2, 4-dicyanopyrido[1,2-a]benzimidazoles

A high throughput screen showed the ability of a 1-amino-2,4-dicyanopyrido[1,2-a]benzimidazole analogue to directly inhibit the lytic activity of the pore-forming protein perforin. A series of analogues were prepared to study structure-activity relationships (SAR) for the this activity, either directly added to cells or released in situ by KHYG-1 NK cells, at non-toxic concentrations. These studies showed that the pyridobenzimidazole moiety was required for effective activity, with strongly basic centres disfavoured. This class of compounds was relatively unaffected by the addition of serum, which was not the case for a previous class of direct inhibitors

Oligothiophene Nanoparticles: Photophysical and Electrogenerated Chemiluminescence Studies

Thiophene oligomer nanoparticles (NPs) were studied by fluorescence spectroscopy and electrogenerated chemiluminescence (ECL). Distinct spectroscopic differences between aggregates or NPs of thiophene hexamers having differing substitution patterns of solubilizing alkyl groups were observed. The α,ω-unsubstituted thiophene hexamer, <b>Hexamer-2</b>, exhibited fluorescence properties that were similar in solution and as colloidal NPs; there was only a small red shift compared with what was observed for the discrete system dissolved in tetrahydrofuran (THF). In contrast, the oligomer substituted in the α,ω-positions with branched alkyl substituents (<b>Hexamer-1</b>) displayed a gradual bathochromic shift of the fluorescence maximum in proportion to the amount of a poor solvent (water) added to the THF solution. Moreover, the fluorescence characteristics for the oligomer(s) dissolved in a mixture of THF and water were similar to those seen by annihilation ECL in a mixture of benzene/acetonitrile. On this basis, we conclude that annihilation ECL may be a useful technique for monitoring the formation of organic nanoparticles

Exploration of a series of 5-arylidene-2-thioxoimidazolidin-4-ones as inhibitors of the cytolytic protein perforin

A series of novel 5-arylidene-2-thioxoimidazolidin-4-ones were investigated as inhibitors of the lymphocyte-expressed pore-forming protein perform. Structure activity relationships were explored through variation of an isoindolinone or 3,4-dihydroisoquinolinone subunit on a fixed 2-thioxoimidazolidin-4-one/thiophene core. The ability of the resulting compounds to inhibit the lytic activity of both isolated perform protein and perforin delivered in situ by natural killer cells was determined. A number of compounds showed excellent activity at concentrations that were nontoxic to the killer cells, and several were a significant improvement on previous classes of inhibitors, being substantially more potent and soluble. Representative examples showed rapid and reversible binding to immobilized mouse perforin at low concentrations

Exploration of a series of 5-arylidene-2-thioxoimidazolidin-4-ones as inhibitors of the cytolytic protein perforin

A series of novel 5-arylidene-2-thioxoimidazolidin-4-ones were investigated as inhibitors of the lymphocyte-expressed pore-forming protein perform. Structure activity relationships were explored through variation of an isoindolinone or 3,4-dihydroisoquinolinone subunit on a fixed 2-thioxoimidazolidin-4-one/thiophene core. The ability of the resulting compounds to inhibit the lytic activity of both isolated perform protein and perforin delivered in situ by natural killer cells was determined. A number of compounds showed excellent activity at concentrations that were nontoxic to the killer cells, and several were a significant improvement on previous classes of inhibitors, being substantially more potent and soluble. Representative examples showed rapid and reversible binding to immobilized mouse perforin at low concentrations

Spectral Dependence of the Internal Quantum Efficiency of Organic Solar Cells: Effect of Charge Generation Pathways

The conventional picture of photocurrent generation in organic solar cells involves photoexcitation of the electron donor, followed by electron transfer to the acceptor via an interfacial charge-transfer state (Channel I). It has been shown that the mirror-image process of acceptor photoexcitation leading to hole transfer to the donor is also an efficient means to generate photocurrent (Channel II). The donor and acceptor components may have overlapping or distinct absorption characteristics. Hence, different excitation wavelengths may preferentially activate one channel or the other, or indeed both. As such, the internal quantum efficiency (IQE) of the solar cell may likewise depend on the excitation wavelength. We show that several model high-efficiency organic solar cell blends, notably PCDTBT:​PC70BM and PCPDTBT:​PC60/70BM, exhibit flat IQEs across the visible spectrum, suggesting that charge generation is occurring either via a dominant single channel or via both channels but with comparable efficiencies. In contrast, blends of the narrow optical gap copolymer DPP-DTT with PC70BM show two distinct spectrally flat regions in their IQEs, consistent with the two channels operating at different efficiencies. The observed energy dependence of the IQE can be successfully modeled as two parallel photodiodes, each with its own energetics and exciton dynamics but both having the same extraction efficiency. Hence, an excitation-energy dependence of the IQE in this case can be explained as the interplay between two photocurrent-generating channels, without recourse to hot excitons or other exotic processes