Perovskite-organic tandem solar cells with indium oxide interconnect.

Multijunction solar cells can overcome the fundamental efficiency limits of single-junction devices. The bandgap tunability of metal halide perovskite solar cells renders them attractive for multijunction architectures1. Combinations with silicon and copper indium gallium selenide (CIGS), as well as all-perovskite tandem cells, have been reported2-5. Meanwhile, narrow-gap non-fullerene acceptors have unlocked skyrocketing efficiencies for organic solar cells6,7. Organic and perovskite semiconductors are an attractive combination, sharing similar processing technologies. Currently, perovskite-organic tandems show subpar efficiencies and are limited by the low open-circuit voltage (Voc) of wide-gap perovskite cells8 and losses introduced by the interconnect between the subcells9,10. Here we demonstrate perovskite-organic tandem cells with an efficiency of 24.0 per cent (certified 23.1 per cent) and a high Voc of 2.15 volts. Optimized charge extraction layers afford perovskite subcells with an outstanding combination of high Voc and fill factor. The organic subcells provide a high external quantum efficiency in the near-infrared and, in contrast to paradigmatic concerns about limited photostability of non-fullerene cells11, show an outstanding operational stability if excitons are predominantly generated on the non-fullerene acceptor, which is the case in our tandems. The subcells are connected by an ultrathin (approximately 1.5 nanometres) metal-like indium oxide layer with unprecedented low optical/electrical losses. This work sets a milestone for perovskite-organic tandems, which outperform the best p-i-n perovskite single junctions12 and are on a par with perovskite-CIGS and all-perovskite multijunctions13.

Making Graphene Nanoribbons Photoluminescent.

We demonstrate the alignment-preserving transfer of parallel graphene nanoribbons (GNRs) onto insulating substrates. The photophysics of such samples is characterized by polarized Raman and photoluminescence (PL) spectroscopies. The Raman scattered light and the PL are polarized along the GNR axis. The Raman cross section as a function of excitation energy has distinct excitonic peaks associated with transitions between the one-dimensional parabolic subbands. We find that the PL of GNRs is intrinsically low but can be strongly enhanced by blue laser irradiation in ambient conditions or hydrogenation in ultrahigh vacuum. These functionalization routes cause the formation of sp3 defects in GNRs. We demonstrate the laser writing of luminescent patterns in GNR films for maskless lithography by the controlled generation of defects. Our findings set the stage for further exploration of the optical properties of GNRs on insulating substrates and in device geometries.

Downmodulation of key inflammatory cell markers with a topical Janus kinase 1/2 inhibitor.

BACKGROUND: INCB018424 is a novel, potent Janus kinase (JAK)1/JAK2 inhibitor that blocks signal transduction of multiple proinflammatory cytokines. OBJECTIVES: To evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics and preliminary efficacy of topical INCB018424 phosphate cream in patients with plaque psoriasis. METHODS: Topical INCB018424 phosphate 1·0% or 1·5% cream was applied once daily (QD) or twice daily (BID) for 4 weeks to 2-20% body surface area in five sequential cohorts of five patients aged 18-65 years. Target lesions were scored on a scale of 0-4 for erythema, scaling and thickness. Additionally, the overall disease activity in each patient was measured using Physician's Global Assessment. INCB018424 concentrations were measured in plasma, and cytokine stimulated phosphorylated signal transducer and activator of transcription 3 phosphorylation (pSTAT3) levels in peripheral blood cells were evaluated. Pretreatment and post-treatment skin biopsies were compared with healthy skin, including evaluation of histopathology, immunohistochemistry and mRNA expression. RESULTS: Treatment with INCB018424 phosphate cream either 1·0% QD or 1·5% BID resulted in improvements in lesion scores. No significant inhibition of pSTAT3 in peripheral blood cells was observed following topical application, consistent with the generally low steady-state plasma concentrations of INCB018424 measured. Transcriptional markers of immune cell lineage/activation in lesional skin were reduced by topical INCB018424, with correlations observed between clinical improvement and decreases in markers of T helper 17 lymphocyte activation, dendritic-cell activation and epidermal hyperplasia. INCB018424 treatment reduced epidermal hyperplasia and dermal inflammation in most patient samples, with reductions in CD3, CD11c, Ki67 and keratin 16 observed by immunohistochemical analysis. CONCLUSIONS: Topical INCB018424 dosed for 28 days QD or BID is pharmacologically active in patients with active psoriasis and modulates proinflammatory cytokines in the pathogenesis of psoriatic lesions.

Visualizing charge separation in bulk heterojunction organic solar cells.

Solar cells based on conjugated polymer and fullerene blends have been developed as a low-cost alternative to silicon. For efficient solar cells, electron-hole pairs must separate into free mobile charges that can be extracted in high yield. We still lack good understanding of how, why and when carriers separate against the Coulomb attraction. Here we visualize the charge separation process in bulk heterojunction solar cells by directly measuring charge carrier drift in a polymer:fullerene blend with ultrafast time resolution. We show that initially only closely separated (<1 nm) charge pairs are created and they separate by several nanometres during the first several picoseconds. Charge pairs overcome Coulomb attraction and form free carriers on a subnanosecond time scale. Numerical simulations complementing the experimental data show that fast three-dimensional charge diffusion within an energetically disordered medium, increasing the entropy of the system, is sufficient to drive the charge separation process.

Electric field assisted charge carrier photogeneration in poly(spirobifluorene-co-benzothiadiazole).

The dynamics of charge carrier generation in poly(spirobifluorene-co-benzothiadiazole) was investigated by electric field-induced fluorescence quenching and differential absorption measurements. Three different time domains of carrier generation have been identified: an ultrafast phase, a subnanosecond phase, and an entire lifetime phase. The charge generation efficiencies during the first and second phases were found to be almost independent of temperature, being about 25% and 10%, respectively, at an applied electric field of 1.3×10(6) V/cm, while the generation efficiency during the third phase increases from 2% at 80 K to 10% at room temperature. The results of transient spectroscopy measurements and quantum chemical calculations suggest an intramolecular charge transfer for about 1 ps from the alkoxy-substituted fluorene side group to the benzothiadiazole subunit of the main chain. The formation and evolution of the resulting charge transfer states determine the way of charge carrier generation.

An Andean radiation: polyploidy in the tree genus Polylepis (Rosaceae, Sanguisorbeae).

The Andean tree genus Polylepis (Rosaceae) is notorious for the high morphological plasticity of its species and the difficulty in their circumscription. The evolutionary mechanisms that have driven diversification of the genus are still poorly understood, with factors as diverse as ecological specialisation, reticulate evolution, polyploidisation and apomixis being proposed to contribute. In the present study, chromosome counts, flow cytometry and stomata guard cell size measurements were employed to document for the first time the presence of polyploidy in the genus and to infer ploidy levels for most species. Inferred ploidy levels show a clear progression from diploidy in cloud forest species to polyploidy (tetra- to octoploidy) in the morphologically and ecologically specialised incana group, indicating that polyploidisation may have played a major role in speciation processes and the colonisation of novel habitats during the Andean uplift. At least two species of Polylepis comprise populations with varying degrees of ploidy. More extensive studies are needed to obtain a better understanding of the prevalence and effects of intraspecific polyploidy in the genus.

Ultrafast dynamics of carrier mobility in a conjugated polymer probed at molecular and microscopic length scales.

We used time-resolved electric-field-induced second-harmonic generation to probe the charge-carrier-mobility dynamics in amorphous organic materials on an ultrafast time scale. We were able to show that the mobility in poly-spiro-bifluorene-co-benzothiadiazol decreases from 0.1 cm 2/V s at 1 ps to 10-6 cm2/V s within 1 mus. We attribute this dramatic decrease to the relaxation of the charge carriers within the density of states, clearly demonstrating the impact of disorder on the nanoscale charge transport in amorphous semiconductors.

Triplet-polaron quenching in conjugated polymers.

We studied the triplet-polaron quenching in a platinum(II) porphyrin- (PtOEP-) doped polyspirobifluorene (PSF-TAD) copolymer. The copolymer contains a hole-transporting phenylenediamine unit (TAD) as a comonomer. Triplet-polaron quenching was probed by the change in PtOEP phosphorescence lifetime under an applied voltage in a unipolar device. The charge-induced reduction of the optically excited lifetime of PtOEP is one-third for the highest applied bias. The charge density can be obtained from current-voltage characteristics in the space-charge-limited (SCL) regime. The obtained hole mobility under SCL conditions is (7 +/- 2) x 10(-5) cm(2)/(V s). This result is in accord with recent mobility measurements of the time-of-flight mobility in our polymer. The triplet-polaron recombination constant was evaluated to be (4 +/- 1) x 10(-13) cm(3)/s, implying a triplet-polaron interaction radius of 2 x 10(-10) m. The results show that triplet-polaron annihilation cannot be neglected in device models for phosphorescent light-emitting diodes.

Exciton diffusion and relaxation in methyl-substituted polyparaphenylene polymer films.

Exciton diffusion in ladder-type methyl-substituted polyparaphenylene film and solution was investigated by means of femtosecond pump-probe spectroscopy using a combined approach, analyzing exciton-exciton annihilation, and transient absorption depolarization properties. We show that the different views on the exciton dynamics offered by anisotropy decay and annihilation are required in order to obtain a correct picture of the energy transfer dynamics. Comparison of the exciton diffusion coefficient and exciton diffusion radius obtained for polymer film with the two techniques reveals that there is substantial short-range order in the film. Also in isolated chains there is considerable amount of order, as revealed from only partial anisotropy decay, which shows that only a small fraction of the excitons move to differently oriented polymer segments. It is further concluded that interchain energy transfer is faster than intrachain transfer, mainly as a result of shorter interchain distances between chromophoric units.

Transdermal fentanyl in the long-term treatment of cancer pain: a prospective study of 50 patients with advanced cancer of the gastrointestinal tract or the head and neck region.

This open prospective study evaluated the combination of initial dose titration with patient-controlled analgesia (PCA) and long-term treatment with transdermal fentanyl in 50 cancer patients requiring opioids for severe pain. The delivery rate of the first transdermal therapeutic system (TTS) was calculated from the self-administered intravenous fentanyl dose during the first 24 h. TTS were changed every 48-72 h, and a different patch size was chosen if necessary. Pain intensity (101-step numeric analog scale) and side-effects were assessed daily. The patients were treated for 66 +/- 101 days (range 3-535 days). The average delivery rate was 5.9 +/- 4.1 mg/d. Mean pain intensity decreased from initially 45 +/- 21 to 19 +/- 15 in the titration phase and 15 +/- 11 during long-term treatment. Three patients showed moderate respiratory depression. Other severe side-effects were not observed. Patient compliance and acceptance were excellent. The results suggest that intravenous PCA is useful for initial dose finding, and transdermal fentanyl is effective and safe during long-term treatment of cancer pain.