Near-infrared absorbing acceptor with suppressed triplet exciton generation enabling high performance tandem organic solar cells.

Reducing the energy loss of sub-cells is critical for high performance tandem organic solar cells, while it is limited by the severe non-radiative voltage loss via the formation of non-emissive triplet excitons. Herein, we develop an ultra-narrow bandgap acceptor BTPSeV-4F through replacement of terminal thiophene by selenophene in the central fused ring of BTPSV-4F, for constructing efficient tandem organic solar cells. The selenophene substitution further decrease the optical bandgap of BTPSV-4F to 1.17 eV and suppress the formation of triplet exciton in the BTPSV-4F-based devices. The organic solar cells with BTPSeV-4F as acceptor demonstrate a higher power conversion efficiency of 14.2% with a record high short-circuit current density of 30.1 mA cm-2 and low energy loss of 0.55 eV benefitted from the low non-radiative energy loss due to the suppression of triplet exciton formation. We also develop a high-performance medium bandgap acceptor O1-Br for front cells. By integrating the PM6:O1-Br based front cells with the PTB7-Th:BTPSeV-4F based rear cells, the tandem organic solar cell demonstrates a power conversion efficiency of 19%. The results indicate that the suppression of triplet excitons formation in the near-infrared-absorbing acceptor by molecular design is an effective way to improve the photovoltaic performance of the tandem organic solar cells.

Biochemical Characterization of a GH46 Chitosanase Provides Insights into the Novel Digestion Specificity.

Endo-chitosanases (EC 3.2.1.132) are generally considered to selectively release functional chito-oligosaccharides (COSs) with degrees of polymerization (DPs) ≥ 2. Although numerous endo-chitosanases have been characterized, the digestion specificity of endo-chitosanases needs to be further explored. In this study, a GH46 endo-chitosanase OUC-CsnPa was cloned, expressed, and characterized from Paenibacillus sp. 1-18. The digestion pattern analysis indicated that OUC-CsnPa could produce monosaccharides from chitotetraose [(GlcN)4], the smallest recognized substrate, in a random endo-acting manner. Especially, the enzyme specificities during chitosan digestion including the regulation of product abundance through a transglycosylation reaction were also evaluated. It was hypothesized that an insertion region in OUC-CsnPa may form a strong force to be involved in stabilizing (GlcN)4 at its negative subsite for efficient hydrolysis. This is the first comprehensive report to reveal the digestion specificity and subsite specificity of monosaccharide production by endo-chitosanases. Overall, OUC-CsnPa described here highlights the previously unknown digestion properties of the endo-acting chitosanases and provides a unique example of possible structure-function relationships.

Insights into promiscuous chitosanases: the known and the unknown.

Chitosanase, a glycoside hydrolase (GH), catalyzes the cleavage of ß-1,4-glycosidic bonds in polysaccharides and is widely distributed in nature. Many organisms produce chitosanases, and numerous chitosanases in the GH families have been intensely studied. The reported chitosanases mainly cleaved the inter-glucosamine glycosidic bonds, while substrate specificity is not strictly unique due to the existence of bifunctional or multifunctional activity profiles. The promiscuity of chitosanases is essential for the different pathways of biomass polysaccharide conversion and understanding of the chitosanase evolutionary process. However, the reviews for this aspect are completely unknown. This review provides an overview of the promiscuous activities, also considering the substrate and product specificity of chitosanases observed to date. These contribute to important implications for the future discovery and research of promiscuous chitosanases and applications related to biomass conversion. KEY POINTS: • The promiscuity of chitosanases is reviewed for the first time. • The current review provides insights into the substrate specificity of chitosanases. • The mode-product relationship and prospect of promiscuous chitosanases are highlighted.

Inorganic-Organic Hybrid Phototransistor Array with Enhanced Photogating Effect for Dynamic Near-Infrared Light Sensing and Image Preprocessing.

Narrow-band-gap organic semiconductors have emerged as appealing near-infrared (NIR) sensing materials by virtue of their unique optoelectronic properties. However, their limited carrier mobility impedes the implementation of large-area, dynamic NIR sensor arrays. In this work, high-performance inorganic-organic hybrid phototransistor arrays are achieved for NIR sensing, by taking advantage of the high electron mobility of In2O3 and the strong NIR absorption of a BTPV-4F:PTB7-Th bulk heterojunction (BHJ) with an enhanced photogating effect. As a result, the hybrid phototransistors reach a high responsivity of 1393.0 A W-1, a high specific detectivity of 4.8 × 1012 jones, and a fast response of 0.72 ms to NIR light (900 nm). Meanwhile, an integrated 16 × 16 phototransistor array with a one-transistor-one-phototransistor (1T1PT) architecture is achieved. On the basis of the enhanced photogating effect, the phototransistor array can not only achieve real-time, dynamic NIR light mapping but also implement image preprocessing, which is promising for advanced NIR image sensors.

New Insights into Bifunctional Chitosanases with Hydrolysis Activity toward Chito- and Cello-Substrates.

In the present study, we carried out a comprehensive investigation of glycoside hydrolase (GH) 46 model-chitosanases based on cleavage specificity classification to understand their unknown bifunctional activity. We for the first time show that GH46 chitosanase CsnMHK1 from Bacillus circulans MH-K1, which was previously thought to be strictly exclusive to chitosan, can hydrolyze both chito- and cello-substrates. We determined the digestion direction of bifunctional chitosanase CsnMHK1 from class III and compared it with class II chitosanase belonging to GH8, providing insight into unique substrate specificities and a new perspective on its reclassification. The results lead us to challenge the current understanding of chitosanase substrate specificity based on GH taxonomy classification and suggest that the prevalence from the common bifunctional activity may have occurred. Altogether, these data contribute to the understanding of chitosanase recognition and hydrolysis toward chito- and cello-substrates, which is valuable for future studies on chitosanases.

Constructing Monolithic Perovskite/Organic Tandem Solar Cell with Efficiency of 22.0% via Reduced Open-Circuit Voltage Loss and Broadened Absorption Spectra.

Combining the high stability under UV light of the wide bandgap (WBG) perovskite solar cells (pero-SCs) and the broad near-infrared absorption spectra of the narrow bandgap (NBG) organic solar cells (OSCs), the perovskite/organic tandem solar cells (TSCs) with the WBG pero-SC as front cell and the NBG OSC as rear cell have attracted attention . However, the photovoltaic performance of the perovskite/organic TSCs needs to be further improved. Herein, nonradiative charge recombination loss is reduced through bulk defect passivation in the WBG pero-SC front subcell and broadening the range of absorption spectra of the NBG OSC rear cell. For the WBG pero-SCs, an organic cation chloro-formamidinium is introduced into FA0.6 MA0.4 Pb(I0.6 Br0.4 )3 to passivate the bulk defects in the perovskite film and the WBG pero-SC displays high open-circuit voltage of 1.25 V and high fill factor of 83.0%. For the NBG OSCs, a new infrared-absorbing organic small molecule acceptor BTPV-4Cl-eC9 is designed and synthesized. Then, a monolithic perovskite/organic TSC is fabricated with the WBG pero-SC as the front cell and the NBG OSC as the rear cell, and the TSC demonstrates high power conversion efficiency up to 22.0%. The results indicate that the perovskite/organic TSC is promising for future commercialization.

High performance tandem organic solar cells via a strongly infrared-absorbing narrow bandgap acceptor.

Tandem organic solar cells are based on the device structure monolithically connecting two solar cells to broaden overall absorption spectrum and utilize the photon energy more efficiently. Herein, we demonstrate a simple strategy of inserting a double bond between the central core and end groups of the small molecule acceptor Y6 to extend its conjugation length and absorption range. As a result, a new narrow bandgap acceptor BTPV-4F was synthesized with an optical bandgap of 1.21 eV. The single-junction devices based on BTPV-4F as acceptor achieved a power conversion efficiency of over 13.4% with a high short-circuit current density of 28.9 mA cm-2. With adopting BTPV-4F as the rear cell acceptor material, the resulting tandem devices reached a high power conversion efficiency of over 16.4% with good photostability. The results indicate that BTPV-4F is an efficient infrared-absorbing narrow bandgap acceptor and has great potential to be applied into tandem organic solar cells.

Strengthened Perovskite/Fullerene Interface Enhances Efficiency and Stability of Inverted Planar Perovskite Solar Cells via a Tetrafluoroterephthalic Acid Interlayer.

In this work, a novel back contact interface engineering is developed for inverted planar perovskite solar cells, in which a tetrafluoroterephthalic acid (TFTPA) interlayer is inserted between CH3NH3PbI3 and PC61BM to strengthen the interface contact. Benefiting from the strong Coulombic interactions between positive electron-poor tetrafluoroterephthalate moieties and negative electron-rich fullerene molecules, as well as the coordinate effect between -COOH groups of TFTPA and Pb2+ ions of perovskites surface, a tightly jointing and defect-passivated CH3NH3PbI3/PC61BM interface is formed. The strengthened CH3NH3PbI3/PC61BM back contact can significantly facilitate electron transport and simultaneously diminish the charge accumulation and recombination. Therefore, power conversion efficiency (PCE) of the TFTPA device is up to 19.39%, whereas the hysteresis effect is weak, and the PCE is improved by 20.4% compared with the control device which does not have a TFTPA interlayer. Particularly, the moisture stability of the TFTPA device is greatly improved as compared to the control device. Our findings illustrate that the back contact interface engineering is an important and promising approach for inverted planar perovskite solar cells.

Self-assembly of all-conjugated block copolymer nanoparticles with tailoring size and fluorescence for live cell imaging.

A series of all-conjugated polythiophene diblock copolymers containing hydrophobic (hexyl) and hydrophilic (triethylene glycol) side chains were synthesized via a nickel-catalyzed quasi-living polymerization. The correlations between block ratios and the self-assembled nanostructures of the block copolymers in thin films and in various solutions were examined. The copolymers dispersed in water via a slow dialysis method produced molecular-level self-assembled core-shell nanospheres with a crystallized hydrophobic core and a hydrophilic amorphous shell, which was proved by TEM images. The size and quantum yield of polymer micelles could be easily tuned via the block ratio of copolymers. The resulting core-shell nanospheres of BP40 composed of 40 mol% P3HT blocks with an average size of 120 nm exhibit high quantum yield (19% in aqueous medium), good photostability and low cytotoxicity. Utilized as a far-red/near-infrared (FR/NIR) cellular probe, BP40 is internalized efficiently by the cells and accumulated in the cytoplasm to give bright fluorescence.

Photonic microwave waveforms generation based on time-domain processing.

A new photonic approach of microwave waveform generator based on time-domain synthesis is proposed and experimentally demonstrated, in which two single-drive Mach-Zehnder modulators biased at quadrature point are severed as optical pulse carvers and various microwave waveforms can be generated by carving and overlapping optical field envelopes. The theoretical analysis and simulation are developed. In experiment, a square waveform with 50% duty cycle, triangular waveform with full duty cycle, and sawtooth (or reversed-sawtooth) waveform with 50% duty cycle are generated. Furthermore, a frequency doubling sawtooth (or reversed-sawtooth) waveform with full duty cycle is also obtained.