Structure–Activity Relationship between Crystallinity and Carrier Transport of Two-Dimensional Donor Units in Organic Solar Cells

Benzo[1,2-b:4,5-b′]­dithiophene (BDT) and its derivatives have made important contributions to constructing high-performance polymers. However, it is difficult to clarify the real role of donor units due to the interference of strong electronegativity and crystallinity of acceptor units in the D–A copolymer. Here, we design a cyclohexane-substituted dithieno[3,2-f:2′,3′-h]­quinoxaline (DTQ)-based acceptor unit with successfully destroyed crystallinity and charge transport. Three donor-dominated materials PQH-BTF, PQH-BTCl, and PQH-BFCl are obtained. It is found that the materials exhibit obvious differences after destroying the crystallization and charge transport of the acceptor unit, and the real role of different two-dimensional donor units in designed polymers is confirmed. The backbone BDF exhibits much stronger intermolecular interactions compared to BDT, while the side chain ThF demonstrates a higher crystallization capacity than that of ThCl. More interestingly, it can be inferred that the molecular backbone is likely to construct miscible-phase crystallization (D–A crystal) while the side chain tends to demonstrate a capacity for pure-phase crystallization (D–D crystal) in a 2D donor system. Different crystallization leads to different exciton transport: pure-phase crystallization is conducive to the reduction of trap-assisted recombination, while miscible crystallization is beneficial to the reduction of bimolecular recombination. This work can help to choose donor units more accurately when preparing D–A copolymers

Enhanced Photovoltaic Properties Induced by Ferroelectric Domain Structures in Organometallic Halide Perovskites

Organometallic halide perovskites have drawn substantial interest due to their outstanding performance in solar energy conversion and optoelectronic applications. The presence of ferroelectric domain walls in these materials has shown to have a profound effect on their electronic structure. Here, we use a density-functional-based tight-binding model, coupled to nonequilibrium Green’s function method, to investigate the effects of ferroelectric domain walls on electronic transport properties and charge carrier recombination in methylammonium lead–iodide perovskite, MAPbI3. With the presence of ferroelectric domain walls, segregation of transport channels for electrons and holes is observed, and the conductance of perovskites is substantially increased due to the reduced band gap. In addition, by taking into account interactions with photons in the vacuum environment, it is found that electron–hole recombination in perovskites with ferroelectric domain walls is drastically suppressed due to the segregation of carrier transport paths, which could enhance photovoltaic performance

Graphdiyne as a Host Active Material for Perovskite Solar Cell Application

This work demonstrates a novel photovoltaic application in which graphdiyne (GD) can be employed as a host material in a perovskite active layer for the first time. In the device fabrication, the best molar ratio for active materials is verified as PbI2/MAI/GD being 1:1:0.25, yielding a peak power-conversion efficiency of 21.01%. We find that graphdiyne, as the host material, exerts significant influence on the crystallization, film morphology, and a series of optoelectronic properties of the perovskite active layer. A uniform MAPbI(3) film with highly crystalline qualities, large domain sizes, and few grain boundaries was realized with the introduction of graphdiyne. Moreover, the current-voltage hysteresis was negligible, and device stability was significantly improved as well. The results indicate that graphdiyne as the host active material presents great potential for the enhancement of the performance of perovskite solar cells

Whole-gene analysis of two groups of hepatitis B virus C/D inter-genotype recombinant strains isolated in Tibet, China

<div><p>Tibet is a highly hepatitis B virus (HBV) endemic area. Two types of C/D recombinant HBV are commonly isolated in Tibet and have been previously described. In an effort to better understand the molecular characteristic of these C/D recombinant strains from Tibet, we undertook a multistage random sampling project to collect HBsAg positive samples. Molecular epidemiological and bio-informational technologies were used to analyze the characteristics of the sequences found in this study. There were 60 samples enrolled in the survey, and we obtained 19 whole-genome sequences. 19 samples were all C/D recombinant, and could be divided into two sub-types named C/D1 and C/D2 according to the differences in the location of the recombinant breakpoint. The recombination breakpoint of the 10 strains belonging to the C/D1 sub-type was located at nt750, while the 9 stains belonging to C/D2 had their recombination break point at nt1530. According to whole-genome sequence analysis, the 19 identified strains belong to genotype C, but the nucleotide distance was more than 5% between the 19 strains and sub-genotypes C1 to C15. The distance between C/D1with C2 was 5.8±2.1%, while the distance between C/D2 with C2 was 6.4±2.1%. The parental strain was most likely sub-genotype C2. C/D1 strains were all collected in the middle and northern areas of Tibet including Lhasa, Linzhi and Ali, while C/D2 was predominant in Shannan in southern Tibet. This indicates that the two recombinant genotypes are regionally distributed in Tibet. These results provide important information for the study of special HBV recombination events, gene features, virus evolution, and the control and prevention policy of HBV in Tibet.</p></div

Nucleotide distance (%) among the two types of C/D recombinant strains and other reference genotype and subgenotype strains.

<p>Nucleotide distance (%) among the two types of C/D recombinant strains and other reference genotype and subgenotype strains.</p

Basic information of 19 HBV whole-genome sequences obtained from Tibet.

<p>Basic information of 19 HBV whole-genome sequences obtained from Tibet.</p

The results of bootscan analysis demonstrate the recombination of genotypes C and D.

<p>As shown in part A, TibetAli-1, which represents the C/D1 recombinant, was compared with eight representative HBV genotypes—A, B, C, D, E, F, G and H (GenBank accessions: M57663, AB205121, AB205125, AY161150, AB205192, AB166850, AV058513, AY090454, respectively). The recombinant position is at nt 750. As shown in part B, TibetShannan-1 represents C/D2; the recombinant position is at nt 1530bp.As shown in part C, genotype A represents the non-recombinant strain.</p