Polymerizing M-Series Acceptors for Efficient Polymer Solar Cells: Effect of the Molecular Shape.

Currently, high-performance polymerized small-molecule acceptors (PSMAs) based on ADA-type SMAs are still rare and greatly demanded for polymer solar cells (PSCs). Herein, two novel regioregular PSMAs (PW-Se and PS-Se) are designed and synthesized by using centrosymmetric (linear-shaped) and axisymmetric (banana-shaped) ADA-type SMAs as the main building blocks, respectively. It is demonstrated that photovoltaic performance of the PSMAs can be significantly improved by optimizing the configuration of ADA-type SMAs. Compared to the axisymmetric SMA-based polymer (PS-Se), PW-Se using a centrosymmetric SMA as the main building block exhibits better backbone coplanarity thereby resulting in bathochromically shifted absorption with a higher absorption coefficient, tighter interchain π-π stacking, and more favorable blend film morphology. As a result, enhanced and more-balanced charge transport, better exciton dissociation, and reduced charge recombination are achieved for PW-Se-based devices with PM6 as polymer donor. Benefiting from these positive factors, the optimal PM6:PW-Se-based device exhibits a higher power conversion efficiency (PCE) of 15.65% compared to the PM6:PS-Se-based device (8.90%). Furthermore, incorporation of PW-Se as a third component in the binary active layer of PM6:M36 yields ternary devices with an outstanding PCE of 18.0%, which is the highest value for PSCs based on ADA-type SMAs, to the best of the knowledge.

Molecular mechanism of different flower color formation of Cymbidium ensifolium.

Cymbidium ensifolium is one of the national orchids in China, which has high ornamental value with changeable flower colors. To understand the formation mechanism of different flower colors of C. ensifolium, this research conducted transcriptome and metabolome analyses on four different colored sepals of C. ensifolium. Metabolome analysis detected 204 flavonoid metabolites, including 17 polyphenols, 27 anthocyanins, 75 flavones, 34 flavonols, 25 flavonoids, 18 flavanones, and 8 isoflavones. Among them, purple-red and red sepals contain a lot of anthocyanins, including cyanidin, pelargonin, and paeoniflorin, while yellow-green and white sepals have less anthocyanins detected, and their metabolites are mainly flavonols, flavanones and flavonoids. Transcriptome sequencing analysis showed that the expression levels of the anthocyanin biosynthetic enzyme genes in red and purple-red sepals were significantly higher than those in white and yellow-green sepals of C. ensifolium. The experimental results showed that CeF3'H2, CeDFR, CeANS, CeF3H and CeUFGT1 may be the key genes involved in anthocyanin production in C. ensifolium sepals, and CeMYB104 has been proved to play an important role in the flower color formation of C. ensifolium. The results of transformation showed that the CeMYB104 is involved in the synthesis of anthocyanins and can form a purple-red color in the white perianth of Phalaenopsis. These findings provide a theoretical reference to understand the formation mechanism of flower color in C. ensifolium.

Genome-Wide Identification and Analysis of bHLH Transcription Factors Related to Anthocyanin Biosynthesis in Cymbidium ensifolium.

The basic helix-loop-helix (bHLH) transcription factors are widely distributed across eukaryotic kingdoms and participate in various physiological processes. To date, the bHLH family has been identified and functionally analyzed in many plants. However, systematic identification of bHLH transcription factors has yet to be reported in orchids. Here, 94 bHLH transcription factors were identified from the Cymbidium ensifolium genome and divided into 18 subfamilies. Most CebHLHs contain numerous cis-acting elements associated with abiotic stress responses and phytohormone responses. A total of 19 pairs of duplicated genes were found in the CebHLHs, of which 13 pairs were segmentally duplicated genes and six pairs were tandemly duplicated genes. Expression pattern analysis based on transcriptome data revealed that 84 CebHLHs were differentially expressed in four different color sepals, especially CebHLH13 and CebHLH75 of the S7 subfamily. The expression profiles of CebHLH13 and CebHLH75 in sepals, which are considered potential genes regulating anthocyanin biosynthesis, were confirmed through the qRT-PCR technique. Furthermore, subcellular localization results showed that CebHLH13 and CebHLH75 were located in the nucleus. This research lays a foundation for further exploration of the mechanism of CebHLHs in flower color formation.

Genome-Wide Identification of the MYB Gene Family in Cymbidiumensifolium and Its Expression Analysis in Different Flower Colors.

MYB transcription factors of plants play important roles in flavonoid synthesis, aroma regulation, floral organ morphogenesis, and responses to biotic and abiotic stresses. Cymbidium ensifolium is a perennial herbaceous plant belonging to Orchidaceae, with special flower colors and high ornamental value. In this study, a total of 136 CeMYB transcription factors were identified from the genome of C. ensifolium, including 27 1R-MYBs, 102 R2R3-MYBs, 2 3R-MYBs, 2 4R-MYBs, and 3 atypical MYBs. Through phylogenetic analysis in combination with MYB in Arabidopsis thaliana, 20 clusters were obtained, indicating that these CeMYBs may have a variety of biological functions. The 136 CeMYBs were distributed on 18 chromosomes, and the conserved domain analysis showed that they harbored typical amino acid sequence repeats. The motif prediction revealed that multiple conserved elements were mostly located in the N-terminal of CeMYBs, suggesting their functions to be relatively conserved. CeMYBs harbored introns ranging from 0 to 13 and contained a large number of stress- and hormone-responsive cis-acting elements in the promoter regions. The subcellular localization prediction demonstrated that most of CeMYBs were positioned in the nucleus. The analysis of the CeMYBs expression based on transcriptome data showed that CeMYB52, and CeMYB104 of the S6 subfamily may be the key genes leading to flower color variation. The results lay a foundation for the study of MYB transcription factors of C. ensifolium and provide valuable information for further investigations of the potential function of MYB genes in the process of anthocyanin biosynthesis.

The Cymbidium genome reveals the evolution of unique morphological traits.

The marvelously diverse Orchidaceae constitutes the largest family of angiosperms. The genus Cymbidium in Orchidaceae is well known for its unique vegetation, floral morphology, and flower scent traits. Here, a chromosome-scale assembly of the genome of Cymbidium ensifolium (Jianlan) is presented. Comparative genomic analysis showed that C. ensifolium has experienced two whole-genome duplication (WGD) events, the most recent of which was shared by all orchids, while the older event was the τ event shared by most monocots. The results of MADS-box genes analysis provided support for establishing a unique gene model of orchid flower development regulation, and flower shape mutations in C. ensifolium were shown to be associated with the abnormal expression of MADS-box genes. The most abundant floral scent components identified included methyl jasmonate, acacia alcohol and linalool, and the genes involved in the floral scent component network of C. ensifolium were determined. Furthermore, the decreased expression of photosynthesis-antennae and photosynthesis metabolic pathway genes in leaves was shown to result in colorful striped leaves, while the increased expression of MADS-box genes in leaves led to perianth-like leaves. Our results provide fundamental insights into orchid evolution and diversification.

Over 17% Efficiency of Ternary Organic Photovoltaics Employing Two Acceptors with an Acceptor-Donor-Acceptor Configuration.

Ternary organic photovoltaics (OPVs) were constructed with one wide-band-gap donor PM6 and two A-D-A-type acceptors (M-series M36 and MQ5) with similar chemical structures. Power conversion efficiency (PCE) of the optimal ternary OPVs reaches 17.24% with 20 wt % MQ5 content, arising from a simultaneously increased short circuit current density (JSC) of 25.36 mA cm-2 and a fill factor (FF) of 76.02% as compared to those of two binary OPVs. The photon harvesting of ternary active layers can be maximized by adjusting the MQ5 content by reason of the complementary absorption spectra of M36 and MQ5. The molecular arrangement of PM6 and M36 can be collectively optimized by introducing an appropriate amount of MQ5 as a morphology regulator for facilitating effective charge transportation in ternary active layers. The improved photon harvesting and charge transport in active layers should be two important factors responsible for JSC and FF improvement of optimal ternary OPVs, respectively. More than an 8.8% improvement of PCE is achieved in ternary OPVs with an appropriate amount of MQ5 as the photon-harvesting enhancer and morphology regulator. The huge potential of A-D-A-type materials in constructing highly efficient OPVs can be further exploited based on a ternary strategy.

Different Morphology Dependence for Efficient Indoor Organic Photovoltaics: The Role of the Leakage Current and Recombination Losses.

Efficient indoor organic photovoltaics (OPVs) have attracted strong attention for their application in indoor electronic devices. However, the route to optimal photoactive film morphology toward high-performance indoor devices has remained obscure. The leakage current dominated by morphology exerts distinguishing influence on the performance under different illuminations. We have demonstrated that morphology reoptimization plays an important role in indoor OPVs, and their optimal structural features are different from what we laid out for outdoor devices. For indoor OPVs, in order to facilitate low leakage current, it is essential to enhance the crystallinity, phase separation, and domain purity, as well as keeping small surface roughness of the active layer. Furthermore, considering the reduced bimolecular recombination at low light intensity, we have shown that PM6:M36-based indoor devices can work effectively with a large ratio of the donor and acceptor. Our work correlating structure-performance relation and the route to optimal morphology outlines the control over device leakage current and recombination losses boosting the progress of efficient indoor OPVs.

Regioregular Narrow-Bandgap n-Type Polymers with High Electron Mobility Enabling Highly Efficient All-Polymer Solar Cells.

Narrow-bandgap n-type polymers with high electron mobility are urgently demanded for the development of all-polymer solar cells (all-PSCs). Here, two regioregular narrow-bandgap polymer acceptors, L15 and MBTI, with two electron-deficient segments are synthesized by copolymerizing two dibrominated fused-ring electron acceptors (FREA) with distannylated aromatic imide, respectively. Taking full advantage of the FREA and the imide, both polymer acceptors show narrow bandgap and high electron mobility. Benefiting from the more extended absorption, better backbone ordering, and higher electron mobility than those of its regiorandom analog, the L15-based all-PSC yields a high power conversion efficiency (PCE) of 15.2% when blended with the polymer donor PM6. More importantly, MBTI incorporating a benzothiophene-core FREA segment shows relatively higher frontier molecular orbital levels than L15, forming a cascade-like energy level alignment with L15 and PM6. Based on this, ternary all-PSCs are designed where MBTI is introduced as a guest into the PM6:L15 host system. Thanks to further optimal blend morphology and more balanced charge transport, the PCE is improved up to 16.2%, which is among the highest values for all-PSCs. The results demonstrate that combining an FREA and an aromatic imide to construct regioregular narrow-bandgap polymer acceptors provides an effective approach to fabricate highly efficient all-PSCs.

High-Performance Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors Enabled by Asymmetric Cores with Enhanced Noncovalent Intramolecular Interactions.

Nonfullerene acceptors (MQ3, MQ5, MQ6) are synthesized using asymmetric and symmetric ladder-type heteroheptacene cores with selenophene heterocycles. Although MQ3 and MQ5 are constructed with the same number of selenophene heterocycles, the heteroheptacene core of MQ5 is end-capped with selenophene rings while that of MQ3 is flanked with thiophene rings. With the enhanced noncovalent interaction of O⋅⋅⋅Se compared to that of O⋅⋅⋅S, MQ5 shows a bathochromically shifted absorption band and greatly improved carrier transport, leading to a higher power conversion efficiency (PCE) of 15.64 % compared to MQ3, which shows a PCE of 13.51 %. Based on the asymmetric heteroheptacene core, MQ6 shows an improved carrier transport induced by the reduced π-π stacking distance, related with the increased dipole moment in comparison with the nonfullerene acceptors based on symmetric cores. MQ6 exhibits a PCE of 16.39 % with a VOC of 0.88 V, a FF of 75.66 %, and a JSC of 24.62 mA cm-2 .

Chloroplast characterization and phylogenetic relationship of Cymbidium aloifolium (Orchidaceae).

Cymbidium aloifolium is an epiphytic orchid with high medicinal and ornamental value. In order to get a deeper understanding of C. aloifolium, we determined the complete chloroplast genome of C. aloifolium by Illumina sequencing data. The length of this genome is 157,328 bp, including a couple of inverted repeat (IR) regions of 26,829 bp, a large single-copy (LSC) region of 85,793 bp, and a small single-copy (SSC) region of 17,877 bp. The chloroplast genome comprised of 139 genes, including 78 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. In addition, the phylogenetic analysis based on 17 chloroplast genomes of Orchidaceae indicated that C. mannii was closely related to C. aloifolium. This study will provide more valuable information for the classification and phylogenetic research of Cymbidium genus.

Ladder-Type Heteroheptacenes with Different Heterocycles for Nonfullerene Acceptors.

The design, synthesis, and characterization of two novel nonfullerene acceptors (M8 and M34) based on ladder-type heteroheptacenes with different heterocycles are reported. Replacing the furan heterocycles with the thiophene heterocycles in the heteroheptacene backbone leads to a hypsochromically shifted absorption band and greatly improved carrier transport for the resulting nonfullerene acceptor (M34) although the π-π-stacking distances are barely affected. Bulk-heterojunction polymer solar cells fabricated from M34 and a wide band gap polymer (PM6) as the donor showed a best power conversion efficiency (PCE) of 15.24 % with an open circuit voltage (VOC ) of 0.91 V, much higher than a PCE of 4.21 % and a VOC of 0.83 V for the counterparts based on M8:PM6. These results highlight the importance of key atoms in the construction of high-performance nonfullerene acceptors.

Control over π-π stacking of heteroheptacene-based nonfullerene acceptors for 16% efficiency polymer solar cells.

Nonfullerene acceptors are being investigated for use in polymer solar cells (PSCs), with their advantages of extending the absorption range, reducing the energy loss and therefore enhancing the power conversion efficiency (PCE). However, to further boost the PCE, mobilities of these nonfullerene acceptors should be improved. For nonfullerene acceptors, the π-π stacking distance between cofacially stacked molecules significantly affects their mobility. Here, we demonstrate a strategy to increase the mobility of heteroheptacene-based nonfullerene acceptors by reducing their π-π stacking distances via control over the bulkiness of lateral side chains. Incorporation of 2-butyloctyl substituents into the nonfullerene acceptor (M36) leads to an increased mobility with a reduced π-π stacking distance of 3.45 Å. Consequently, M36 affords an enhanced PCE of 16%, which is the highest among all acceptor-donor-acceptor-type nonfullerene acceptors to date. This strategy of control over the bulkiness of side chains on nonfullerene acceptors should aid the development of more efficient PSCs.

The complete chloroplast genome sequence of Goodyera foliosa（Orchidaceae）.

Goodyera foliosa is a terrestrial orchid in Asia and has been listed as an endangered species in the Red List. In this study, we assembled the complete chloroplast genome of G. foliosa using Illumina sequencing data. Its full-length of 154,008 bp including a pair of invert repeats (IR) regions of 25,045 bp, large single-copy (LSC) region of 83,248 bp, and small single-copy (SSC) region of 20,670 bp. The chloroplast genome contains 127 genes, including 80 protein-coding genes, 39 tRNA genes, and 8 rRNA genes. In addition, the phylogenetic analysis base on 12 chloroplast genomes of Orchidaceae indicates that G. schlechtendaliana is closely related to G. foliosa. Our study would be helpful for the formulation of conservation strategies and further research of G. foliosa.

The complete chloroplast genome sequence of Habenaria ciliolaris (Orchidaceae).

Habenaria ciliolaris is a kind of orchid with ornamental value. In this study, we reported the complete chloroplast genome of H. ciliolaris. The complete chloroplast genome is 154,544 bp in length, consists of a pair of inverted repeat (IR, 25,455 bp) regions, a large single-copy region (LSC, 84,032 bp) and a small single-copy region (SSC, 19,602 bp). It contains 179 genes, including 133 protein-coding genes, 38 tRNAs, and 8 rRNAs. A maximum-likelihood phylogenetic analysis demonstrated a close relationship between H. ciliolaris and Habenaria radiata. This work will be valuable for genetic and phylogenetic studies on H. ciliolaris.

The complete chloroplast genome of Eria corneri (Orchidaceae).

Eria corneri is a perennial epiphytic orchid distributed in southeastern China with high value of ornamental and medicinal. In this study, the complete chloroplast genome sequence of E. corneri was determined from Illumina pair-end sequencing data. The complete chloroplast genome sequence of E. corneri is 150,538 base pairs (bp) in length, including one large single-copy region (LSC, 85,941 bp), one small single-copy region (SSC, 13,099 bp), and a pair of inverted repeat regions (IRs) of 25,749 bp. Besides, the complete chloroplast genome contains 132 genes, including 77 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. Phylogenetic analysis showed that E. corneri was most closely related to Calanthe triplicata and Calanthe davidii. Our study provides a foundation for the identification and genotyping of Eria species.

The complete chloroplast genome sequence of Tainia cordifolia (Orchidaceae).

Tainia cordifolia is a subtropical plant with significant ornamental value. Herein, we determined the complete chloroplast (cp) genome sequence of T. cordifolia using Illumina sequencing data. The whole cp genome is 158,089 bp in size, consisting of a pair of inverted repeats (IR 25,260 bp), a large single-copy region (LSC 86,876 bp), and a small single-copy region (SSC 20,693 bp). Plastid genome contains 136 genes, 88 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. What is more, a maximum-likelihood phylogenetic analysis demonstrated that T. cordifolia was most closely related to Oberonia japonica and Dendrobium salaccense. The cp genome will provide reference for the further investigation and research of T. cordifolia.

The complete chloroplast genome of Tainia dunnii (Orchidaceae): genome structure and evolution.

Tainia dunnii is a terrestrial orchid with high ornamental value. Herein, we assembled the complete chloroplast genome of Tainia dunnii by next-generation sequencing technologies. The complete chloroplast genome sequence of Tainia dunnii is 158,305 base pairs (bp) in length, including a pair of inverted repeat regions (IRs, 25,244 bp), one large single-copy region (LSC, 86,819 bp), one small single-copy region (SSC, 20,998 bp). Besides, the complete chloroplast genome contains 136 genes in total, including 88 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. Phylogenetic analysis showed that Tainia dunnii has the closest relationship with Calanthe davidii and Calanthe triplicata. Our study lay a foundation for further research of Tainia dunnii.

Dithienonaphthalene-Based Non-fullerene Acceptors With Different Bandgaps for Organic Solar Cells.

Compared to the traditional fullerene derivatives, non-fullerene acceptors show more tunable absorption bands as well as adjustable energy levels which are favorable for further PCE enhancement of organic solar cells. In order to enhance light-harvesting property of dithienonaphthalene (DTN)-based acceptors, we designed and synthesized two novel non-fullerene acceptors (DTNIF and DTNSF) based on a ladder-type DTN donor core flanked with two different acceptor units. In combination with a benchmark wide bandgap copolymer (PBDB-T), the best performance device based on DTNIF displayed a high PCE of 8.73% with a short-circuit current (J sc) of 13.26 mA cm-2 and a large fill factor (FF) of 72.77%. With a reduced bandgap of DTNSF, the corresponding best performance device showed an increased J sc of 14.49 mA cm-2 although only a moderate PCE of 7.15% was achieved. These findings offer a molecular design strategy to control the bandgap of DTN-based non-fullerene acceptors with improved light-harvesting.