Free carrier generation and recombination in PbS quantum dot solar cells

Time Delayed Collection Field and Bias Assisted Charge Extraction (BACE) experiments are used to investigate the charge carrier dynamics in PbS colloidal quantum dot solar cells. We find that the free charge carrier creation is slightly field dependent, thus providing an upper limit to the fill factor. The BACE measurements reveal a rather high effective mobility of 2 x 10(-3) cm(2)/Vs, meaning that charge extraction is efficient. On the other hand, a rather high steady state non-geminate recombination coefficient of 3 x 10(-10) cm(3)/s is measured. We, therefore, propose a rapid free charge recombination to constitute the main origin for the limited efficiency of the PbS colloidal quantum dots cells. (C) 2016 AIP Publishing LLC

Combined Application of X-Ray and Neutron Imaging Techniques to Wood Materials

Conservation of Cultural Heritage is extremely important not only from a cultural point of view, but also from a practical one. It is our duty to pass on to future generations the cultural heritage left tous by our ancestors. Wood is one of the most common materials used to generate works of art which are in a state of constant change and/or deterioration. In order to optimize the knowledge of artworks together with their conservation, it is necessary to use the most advanced scientific and technological tools. In the following paper, we will show the results which can be achieved by application of complementary techniques based on the combined use of X-rays and neutrons as structural probes

Magnetic-Field-Induced Recovery Strain in Polycrystalline Ni–Mn–Ga Foam

Recently, we have shown that a polycrystalline Ni–Mn–Ga magnetic shape-memory alloy, when containing two populations of pore sizes, shows very high magnetic-field-induced strain of up to 8.7%. Here, this double-porosity sample is imaged by x-ray microtomography, showing a homogenous distribution of both pore populations. The orientation of six large grains—four with 10M and two with 14M structure—is identified with neutron diffraction. In situ magnetomechanical experiments with a rotating magnetic field demonstrate that strain incompatibilities between misoriented grains are effectively screened by the pores which also stop the propagation of microcracks. During uniaxial compression performed with an orthogonal magnetic bias field, a strain as high as 1% is recovered on unloading by twinning, which is much larger than the elastic value of \u3c0.1% measured without field. At the same time, repeated loading and unloading results in a reduction in the yield stress, which is a training effect similar to that in single crystals

Reliability of charge carrier recombination data determined with charge extraction methods

Charge extraction methods are popular for measuring the charge carrier density in thin film organic solar cells and to draw conclusions about the order and coefficient of nongeminate charge recombination. However, results from such studies may be falsified by inhomogeneous steady state carrier profiles or surface recombination. Here, we present a detailed drift-diffusion study of two charge extraction methods, bias-assisted charge extraction (BACE) and time-delayed collection field (TDCF). Simulations are performed over a wide range of the relevant parameters. Our simulations reveal that both charge extraction methods provide reliable information about the recombination order and coefficient if the measurements are performed under appropriate conditions. However, results from BACE measurements may be easily affected by surface recombination, in particular for small active layer thicknesses and low illumination densities. TDCF, on the other hand, is more robust against surface recombination due to its transient nature but also because it allows for a homogeneous high carrier density to be inserted into the active layer. Therefore, TDCF is capable to provide meaningful information on the order and coefficient of recombination even if the model conditions are not exactly fulfilled. We demonstrate this for an only 100 nm thick layer of a highly efficient nonfullerene acceptor (NFA) blend, comprising the donor polymer PM6 and the NFA Y6. TDCF measurements were performed as a function of delay time for different laser fluences and bias conditions. The full set of data could be consistently fitted by a strict second order recombination process, with a bias- and fluence-independent bimolecular recombination coefficient k(2) = 1.7 x 10(-17)m(3) s(-1). BACE measurements performed on the very same layer yielded the identical result, despite the very different excitation conditions. This proves that recombination in this blend is mostly through processes in the bulk and that surface recombination is of minor importance despite the small active layer thickness. Published under license by AIP Publishing

Mixed domains enhance charge generation and extraction in bulk-heterojunction solar cells with small-molecule donors

The interplay between nanomorphology and efficiency of polymer-fullerene bulk-heterojunction (BHJ) solar cells has been the subject of intense research, but the generality of these concepts for small-molecule (SM) BHJs remains unclear. Here, the relation between performance; charge generation, recombination, and extraction dynamics; and nanomorphology achievable with two SM donors benzo[1,2-b:4,5-b]dithiophene-pyrido[3,4-b]-pyrazine BDT(PPTh2)(2), namely SM1 and SM2, differing by their side-chains, are examined as a function of solution additive composition. The results show that the additive 1,8-diiodooctane acts as a plasticizer in the blends, increases domain size, and promotes ordering/crystallinity. Surprisingly, the system with high domain purity (SM1) exhibits both poor exciton harvesting and severe charge trapping, alleviated only slightly with increased crystallinity. In contrast, the system consisting of mixed domains and lower crystallinity (SM2) shows both excellent exciton harvesting and low charge recombination losses. Importantly, the onset of large, pure crystallites in the latter (SM2) system reduces efficiency, pointing to possible differences in the ideal morphologies for SM-based BHJ solar cells compared with polymer-fullerene devices. In polymer-based systems, tie chains between pure polymer crystals establish a continuous charge transport network, whereas SM-based active layers may in some cases require mixed domains that enable both aggregation and charge percolation to the electrodes

Genomic variations in <i>prn</i> variants of Austrian <i>B</i>. <i>pertussis</i> samples (n = 77) collected from 2002–2008. Frequencies are given as numbers and as percentage of successfully typed samples (in brackets).

<p>¹To distinguish the prn variants Prn1 and Prn7, the sequence of the second polymorphic region is needed as well.</p><p>Genomic variations in <i>prn</i> variants of Austrian <i>B</i>. <i>pertussis</i> samples (n = 77) collected from 2002–2008. Frequencies are given as numbers and as percentage of successfully typed samples (in brackets).</p

Variation of MLVA types in Austrian <i>B</i>. <i>pertussis</i> samples (n = 34) collected from 2002–2006. Frequencies are given as numbers and as percentage of successfully typed samples (in brackets).

<p>Variation of MLVA types in Austrian <i>B</i>. <i>pertussis</i> samples (n = 34) collected from 2002–2006. Frequencies are given as numbers and as percentage of successfully typed samples (in brackets).</p

Primers and probes used in this study.

<p>¹The nucleotide numbering refers to the numbering from the Tohama I genome [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132623#pone.0132623.ref019" target="_blank">19</a>]. Segment accession numbers: BX640414 (<i>prn</i>), BX640422 (<i>ptxP</i>, <i>ptxA</i>, <i>ptxB</i>), BX640416 (<i>fimD</i> and <i>bvgS</i>) and BX640414 (<i>tcfA</i>).</p><p>²The “colder”primer forming only two hydrogen bonds at the specific base has a one base extension at its 5´-end to compensate the reduced T_m.</p><p><b>A,</b> Primers prnAF (top) and prnAR (bottom) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132623#pone.0132623.ref014" target="_blank">14</a>] were used for <i>prn</i> sequencing. <b>B,</b><b>C-1,</b> ARMS-qPCR primers for the determination of the <i>ptxA</i>, <i>ptxB</i>, <i>fimD</i>, <i>bvgS</i> and <i>tcfA</i> alleles <b>(B)</b> as well as for the discrimination between the <i>ptxP1</i>-like and <i>ptxP3</i> alleles <b>(C-1)</b>. For each gene, the forward primer is shown on top, then the reverse primer corresponding to the Tohama I sequence and the reverse primer corresponding to the alternative allele, with the base at the SNP site underlined, and finally the labelled hydrolysis probe. Lower case letters, artificial base replacement with both sequences at the SNP site; FAM, 6-carboxyfluorescein; TET, 4,5,6,7-tetrachlorofluorescein; BHQ1, Black Hole Quencher-1; Cy5, red sulfoindocyanine dye. <b>C-2,</b> oligonucleotides for the <i>fimD</i> non-discriminatory control assay.</p