Achieving Both Enhanced Voltage and Current through Fine‐Tuning Molecular Backbone and Morphology Control in Organic Solar Cells

It is a great challenge to simultaneously improve the two tangled parameters, open circuit voltage (V_oc) and short circuit current density (J_sc) for organic solar cells (OSCs). Herein, such a challenge is addressed by a synergistic approach using fine‐tuning molecular backbone and morphology control simultaneously by a simple yet effective side chain modulation on the backbone of an acceptor–donor–acceptor (A–D–A)‐type acceptor. With this, two terthieno[3,2‐b]thiophene (3TT) based A–D–A‐type acceptors, 3TT‐OCIC with backbone modulation and 3TT‐CIC without such modification, are designed and synthesized. Compared with the controlled molecule 3TT‐CIC, 3TT‐OCIC shows power conversion efficiency (PCE) of 13.13% with improved V_oc of 0.69 V and J_sc of 27.58 mA cm^?2, corresponding to PCE of 12.15% with V_oc of 0.65 V and J_sc of 27.04 mA cm^?2 for 3TT‐CIC–based device. Furthermore, with effective near infrared absorption, 3TT‐OCIC is used as the rear subcell acceptor in a tandem device and gave an excellent PCE of 15.72%.     

Bandgap Narrowing in Non‐Fullerene Acceptors: Single Atom Substitution Leads to High Optoelectronic Response Beyond 1000 nm

Two narrow bandgap non‐fullerene acceptors (NBG‐NFAs), namely, COTIC‐4F and SiOTIC‐4F, are designed and synthesized for the fabrication of efficient near‐infrared organic solar cells (OSCs). The chemical structures of the NBG‐NFAs contain a D′‐D‐D′ electron‐rich internal core based on a cyclopentadithiophene (or dithienosilole) (D) and alkoxythienyl (D′) core, end‐capped with the highly electron‐deficient unit 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile (A), ultimately providing a A‐D′‐D‐D′‐A molecular configuration that enhances the intramolecular charge transfer characteristics of the excited states. One can thereby reduce the optical bandgap (E_g^opt) to as low as ≈1.10 eV, one of the smallest values for NFAs reported to date. In bulk‐heterojunction (BHJ) OSCs, NBG‐NFA blends with the polymer donor PTB7‐Th yield power conversion efficiencies (PCE) of up to 9.0%, which is particularly high when compared against a range of NBG BHJ blends. Most significantly, it is found that, despite the small energy loss (E_g^opt ? eV_OC) of 0.52 eV, the PTB7‐Th/NBG‐NFA bulk heterojunction blends can yield short‐circuit current densities of up to 22.8 mA cm^?2, suggesting that the design and application of NBG‐NFA materials have substantial potential to further improve the PCE of OSCs.     

Pharmacophoric pattern matching in files of three-dimensional chemical structures: Characterization and use of generalized torsion angle screens

This paper describes the use of generalized torsion angles for the screening of conformational searches in databases of three-dimensional chemical structures. A generalized torsion angle is defined as the dihedral angle between two vectors, A₁-A₂ and A₃-A₄, in which none, some, or all of the vectors A₁-A₂, A₂-A₃, and A₃-A₄ correspond to formal chemical bonds. The screens consist of a set of four atoms together with an associated angular range, and are identified by a statistical analysis of the frequencies of occurrence of these features in the Cambridge Structural Database. These frequencies are discussed, and the effectiveness of the screens is demonstrated by an extensive series of searches for representative pharamacophoric patterns.     

High‐Efficiency CsPbI2Br Perovskite Solar Cells with Dopant‐Free Poly(3‐hexylthiophene) Hole Transporting Layers

CsPbI₂Br is emerging as a promising all‐inorganic material for perovskite solar cells (PSCs) due to its more stable lattice structure and moisture resistance compared to CsPbI₃, although its device performance is still much behind this counterpart. Herein, a preannealing process is developed and systematically investigated to achieve high‐quality CsPbI₂Br films by regulating the nucleation and crystallization of perovskite. The preannealing temperature and time are specifically optimized for a dopant‐free poly(3‐hexylthiophene) (P3HT)‐based device to target dopant‐induced drastic performance degradation for spiro‐OMeTAD‐based devices. The resulting P3HT‐based device exhibits comparable power conversion efficiency (PCE) to spiro‐OMeTAD‐based devices but much enhanced ambient stability with over 95% PCE after 1300 h. A diphenylamine derivative is introduced as a buffer layer to improve the energy‐level mismatch between CsPbI₂Br and P3HT. A record‐high PCE of 15.50% for dopant‐free P3HT‐based CsPbI₂Br PSCs is achieved by alleviating the open‐circuit voltage loss with the buffer layer. These results demonstrate that the preannealing processing together with a suitable buffer layer are applicable strategies for developing dopant‐free P3HT PSCs with high efficiency and stability.     

Evaporation‐Free Nonfullerene Flexible Organic Solar Cell Modules Manufactured by An All‐Solution Process

To ensure laboratory‐to‐industry transfer of next‐generation energy harvesting organic solar cells (OSCs), it is necessary to develop flexible OSC modules that can be produced on a continuous roll‐to‐roll basis and to apply an all‐solution process. In this study, nonfullerene acceptors (NFAs)‐based donor polymer, SMD2, is newly designed and synthesized to continuously fabricate high‐performance flexible OSC modules. Also, multifunctional hole transport layers (HTLs), WO₃/HTL solar bilayer HTLs, are developed and applied via an all‐solution process called “ProcessOne” into inverted structure. SMD2, the donor terpolymer, has a deep highest occupied molecular orbital (HOMO) level and can achieve a power conversion efficiency (PCE) of 11.3% with NFAs without any pre‐/post‐treatment because of its optimal balance between crystallinity and miscibility. Furthermore, the integration of multifunctional HTLs enables the recovery of the drop in open circuit voltage (V_OC) caused by a mismatch in energy levels between the deep HOMO level of the NFAs‐based bulk‐heterojunction layer and the solution‐processed HTLs. Also, the photostability under ultraviolet‐exposure necessary for “ProcessOne” is greatly improved because of the integration of multifunctional HTLs. Consequently, because of the synergistic effects of these approaches, the flexible OSC modules fabricated in an industrial production line have a PCE of 5.25% (P_max = 419.6 mW) on an active area of 80 cm².     

A2A R mediated modulation in IP3 levels altering the [Ca2+]i through cAMP-dependent PKA signalling pathway

Stimulation of A_2A receptors (A_2A R) coupled to G_s/olf protein activates Adenylyl cyclase (AC) leading to the release of cAMP which activates the cAMP-dependent PKA phosphorylation. The possible role of A_2A R in the modulation of free cytosolic Ca²⁺ concentration ([Ca²⁺]_i) involving IP₃, cAMP and PKA was investigated in HEK 293-A_2A R. The levels of IP₃ and cAMP were observed by enzyme immunoassay detection method and [Ca²⁺]_i using Fluo-4 AM. Moreover, cAMP-dependent PKA was determined using the PKA Colorimetric Activity Kit. We observed that the cells pre-treated with A_2A R agonist NECA showed increased levels of cAMP, PKA, IP₃ and [Ca²⁺]_i levels. However, the reverse effect was observed with A_2A R antagonists (ZM241385 and caffeine). Blocking the G_αq/PLC/DAG/IP₃ pathway with neomycin, a PLC inhibitor did not affect the modulation of IP₃ and [Ca²⁺]_i levels in HEK 293-A_2A R cells. To investigate the G_αi/AC/cAMP/PKA, HEK 293-A_2A R cells pre-treated with pertussis toxin followed by forskolin in the presence of A_2A R agonist (NECA) showed no effect on cAMP levels. Further, G_αs/AC/cAMP/PKA pathway was investigated to elucidate the role of cAMP-dependent PKA in IP₃ mediated [Ca²⁺]_i modulation. In the HEK 293-A_2A R cells pre-treated with PKA inhibitor KT5720 and treated with NECA led to inhibit the IP₃ and [Ca²⁺]_i levels. The study distinctly demonstrated that A_2A R modulates IP₃ levels to release the [Ca²⁺]_i via cAMP-dependent PKA. The role of A_2A R mediated G_αs pathway inducing IP₃ mediated [Ca²⁺]_i release may open new avenues in the therapy of neurodegenerative disorder.     

A Volume Regulatory Response Can Be Triggered by Nucleosides in Human Erythrocytes, a Perfect Osmometer No Longer

Human erythrocytes have been regarded as perfect osmometers, which swell or shrink as dictated by their osmotic environment. In contrast, in most other cells, swelling elicits a regulatory volume decrease (RVD) modulated by the activation of purinic and pyrimidinic receptors (P receptors). For human erythrocytes this modulation has not been tested, and we thus investigated whether P receptor activation can induce RVD in these cells. Further, because ectonucleotidases may scavenge ATP or ADP or act as a source for extracellular adenosine and therefore modulate P receptor activation and RVD, we also determined their activity in intact erythrocytes. We found relatively low ectoATPase but significant ectoADPase and ectoAMPase activities. When erythrocytes were exposed to hypotonic medium alone, they swelled as expected for an osmometric response and showed no RVD. Activation of P2 receptors by exogenous ATP or ADP did not trigger RVD, whereas P1 agonists adenosine and adenosine-5′-N-ethylcarboxamide induced significant RVD. The effect of adenosine-5′-N-ethylcarboxamide was dose-dependent (maximal RVD of 27%; apparent K_½ of 1.6 ± 1.7 μm). The RVD induced by adenosine was blocked 80% with the non-selective P1 antagonist 8-(p-sulfophenyl theophylline) or the P1-A_2B inhibitor MRS1754, but not by inhibitors of P1 subtypes A₁, A_2A, and A₃. In addition, forskolin (an inducer of intracellular cAMP formation) could mimic the effect of adenosine, supporting the idea of P1-A_2B receptor activation. In conclusion, we report a novel P1-A_2B receptor-mediated RVD activation in mature human erythrocytes and thus indicate that these long held perfect osmometers are not so perfect after all.     

Efficiency Enhancement of Polymer Solar Cells Based on Poly(3‐hexylthiophene)/Indene‐C70 Bisadduct via Methylthiophene Additive

Photovoltaic performance of polymer solar cells based on poly(3‐hexylthiophene) (P3HT) as the donor and indene‐C₇₀ bisadduct (IC₇₀BA) as the acceptor is improved by adding 3 vol% 3‐methylthiophene (MT) or 3‐hexylthiophene (HT) as processing additives. The results of UV‐vis absorption spectroscopy, X‐ray diffraction analysis and atomic force microscopy indicate that with the MT or HT processing additive, the active layer of the blend of P3HT/IC₇₀BA showed strengthened absorbance, enhanced crystallinity and improved film morphology. The power conversion efficiency (PCE) of the PSCs was improved from 5.80% for the device without the additive to 6.35% for the device with HT additive and to 6.69% with MT additive. The PCE of 6.69% is the top value reported so far for the PSCs based on P3HT.     

Work Function Control of Interfacial Buffer Layers for Efficient and Air‐Stable Inverted Low‐Bandgap Organic Photovoltaics

A water‐soluble cationic polythiophene derivative, poly[3‐(6‐{4‐tert‐butylpyridiniumyl}‐hexyl)thiophene‐2,5‐diyl] [P3(TBP)HT], is combined with anionic poly(3,4‐ethylenedioxythiophene):poly(p‐styrenesulfonate) (PEDOT:PSS) on indium tin oxide (ITO) substrates via electrostatic layer‐by‐layer (eLbL) assembly. By varying the number of eLbL layers, the electrode's work function is precisely controlled from 4.6 to 3.8 eV. These polymeric coatings are used as cathodic interfacial modifiers for inverted‐mode organic photovoltaics that incorporate a photoactive layer composed of either poly[(3‐hexylthiophene)‐2,5‐diyl] (P3HT) and the fullerene acceptor [6,6‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) or the low bandgap polymer [poly({4,8‐di(2‐ethylhexyloxyl)benzo[1,2‐b:4,5‐b′]dithiophene}‐2,6‐diyl)‐alt‐({5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}‐1,3‐diyl) (PBDTTPD)] and the electron acceptor [6,6‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM)]. The power conversion efficiency (PCE) of the resulting photovoltaic device is dependent on the composition of the eLbL‐assembled interface and permits the fabrication of devices with efficiencies of 3.8% and 5.6% for P3HT and PBDTTPD donor polymers, respectively. Notably, these devices demonstrate significant stability with a P3HT:PC₆₁BM system maintaining 83% of its original PCE after 1 year of storage and a PBDTTPD:PC₇₁BM system maintaining 97% of its original PCE after over 1000 h of storage in air, according to the ISOS‐D‐1 shelf protocol.     

Evidence for a new early acceptor in Photosystem I of plants. An ESR investigation of reaction center triplet yield and of the reduced intermediary acceptors

The yield of the triplet state of the primary electron donor of Photosystem I of photosynthesis (P^T-700) and the characteristic parameters (g value, line shape, saturation behavior) of the ESR signal of the photoaccumulated intermediary acceptor A have been measured for two types of Photosystem I subchloroplast particles: Triton particles (TSF 1, about 100 chlorophyll molecules per P-700) that contain the iron-sulfur acceptors F_X, F_B and F_A, and lithium dodecyl sulfate (LDS) particles (about 40 chlorophyll molecules per P-700) that lack these iron-sulfur acceptors. The results are: (i) In Triton particles the yield of P^T-700 upon illumination is independent of the redox state of A and of F_X,B,A and is maximally about 5% of the active reaction centers at 5 K. The molecular sublevel decay rates are k_x = 1100 s^?1 ± 10%, k_y = 1300 s^?1 ± 10% and k_z = 83 s^?1 ± 20%. In LDS particles the triplet yield decreases linearly with concentration of reduced intermediary acceptors, the maximal yield being about 4% at 5 K assuming full P-700 activity. (ii) In Triton particles the acceptor complex A consists of two acceptors A₀ and A₁, with A₀ preceding A₁. In LDS particles at temperatures below ?30°C only A₀ is photoactive. (iii) The spin-polarized ESR signal found in the time-resolved ESR experiments with Triton particles is attributed to a polarized P-700-A^?₁ spectrum. The decay kinetics are complex and are influenced by transient nutation effects, even at low microwave power. It is concluded that the lifetime at 5 K of P-700A₀A^?₁ must exceed 5 ms. We conclude that P^T-700 originates from charge recombination of P-700A^?₀, and that in Triton particles A₀ and A₁ are both photoaccumulated upon cooling at low redox potential in the light. Since the state P-700AF^?_X does not give rise to triplet formation the 5% triplet yield in Triton particles is probably due to centers with damaged electron transport.     

Extraction of electron acceptor A1 from pea photosystem I

Photosystem I particles were washed twice in either 0, 50 or 100% water-saturated diethyl ether. It was found that the characteristic electron spin resonance signal associated with electron acceptor A₁ was progressively lost with increasing percentage saturation of the ether. Light-induced electron flow to the terminal iron-sulphur acceptors was inhibited although these acceptors were still present and could be chemically reduced. The kinetics of optical measurements of P700⁺ re-reduction at 820 nm following ether washing were consistent with removal of electron acceptor A₁.     

Significantly Enhancing the Efficiency of a New Light‐Harvesting Polymer with Alkylthio naphthyl Substituents Compared to Their Alkoxyl Analogs

In this work, a new benzo[1,2‐b:4,5‐b′]dithiophene (BDT) building block containing alkylthio naphthyl as a side chain is designed and synthesized, and the resulting polymer, namely PBDTNS‐BDD, shows a lower HOMO energy level than that of its alkoxyl naphthyl counterpart PBDTNO‐BDD. An optimized photovoltaic device using PBDTNS‐BDD as a donor exhibits power conversion efficiencies (PCE) of 8.70% and 9.28% with the fullerene derivative PC₇₁BM and the fullerene‐free small molecule ITIC as acceptors, respectively. Surprisingly, ternary blend devices based on PBDTNS‐BDD and two acceptors, namely PC₇₁BM and ITIC, shows a PCE of 11.21%, which is much higher than that of PBDTNO‐BDD based ternary devices (7.85%) even under optimized conditions.     

Enzymatic characterization of mRNA cap adenosine-N6 methyltransferase PCIF1 activity on uncapped RNAs

The phosphorylated RNA polymerase II CTD interacting factor 1 (PCIF1) is a methyltransferase that adds a methyl group to the N6-position of 2′O-methyladenosine (A_m), generating N6, 2′O-dimethyladenosine (m⁶A_m) when A_m is the cap-proximal nucleotide. In addition, PCIF1 has ancillary methylation activities on internal adenosines (both A and A_m), although with much lower catalytic efficiency relative to that of its preferred cap substrate. The PCIF1 preference for 2′O-methylated A_m over unmodified A nucleosides is due mainly to increased binding affinity for A_m. Importantly, it was recently reported that PCIF1 can methylate viral RNA. Although some viral RNA can be translated in the absence of a cap, it is unclear what roles PCIF1 modifications may play in the functionality of viral RNAs. Here we show, using in vitro assays of binding and methyltransfer, that PCIF1 binds an uncapped 5′-A_m oligonucleotide with approximately the same affinity as that of a cap analog (K_M = 0.4 versus 0.3 μM). In addition, PCIF1 methylates the uncapped 5′-A_m with activity decreased by only fivefold to sixfold compared with its preferred capped substrate. We finally discuss the relationship between PCIF1-catalyzed RNA methylation, shown here to have broader substrate specificity than previously appreciated, and that of the RNA demethylase fat mass and obesity-associated protein (FTO), which demonstrates PCIF1-opposing activities on capped RNAs.     

2′,5′-Adenylate and Cordycepin Trimer Cores: Metabolic Stability and Evidence for Antimitogenesis without 5′-Rephosphorylation

Abstract

The effect of the 2′,5′-adenylate and cordycepin trimer cores on DNA and protein synthesis in human umbilical cord lymphocytes, lymphoblasts, peripheral blood lymphocytes and Epstein-Barr virus infected lymphocytes and their metabolism in tissue culture medium have been studied. [³²P]Adenylate and [³²P]- and [³H]cordycepin trimer cores were synthesized either enzymatically or chemically and added to cells in culture. The half-lives of the 2′,5′-A₃ core and 2′,5′-3′dA₃ core in tissue culture were 3 and 17 hr, respectively. Chromatographic analysis of the TCA-soluble extracts of the lymphocytes and lymphoblasts treated with 2′,5′-[³H]A₃ showed that 0.25% of the ³²P was identified as AMP, ADP, ATP and inorganic phosphate. By the more sensitive 2′,5′-p₃A₄[³²P]pCp radiobinding assay, 2′,5′-A₃ was detected in the TCA supernatants; however, there was no 5′-rephosphorylation. With the [³H]- and [³²P]cordycepin trimer core, 0.55% and 1.3% of the radioactivity was in the TCA soluble extracts. Although there was no 5′-rephosphorylation as determined by radiobinding assay, the intact cordycepin trimer core was detected by tlc, radiobinding assay, and HPLC.

Furthermore, in two experiments, the concentration of the cordycepin trimer core bound to or taken up by the lymphocytes was three-fold greater than the concentration in the medium. 2′,5′-A₃ and 2′,5′-3′dA₃ cores were both antimitogenic, but did not inhibit protein synthesis.     

Functional interaction between purinergic receptors: effect of ligands for A2A and P2Y12 receptors on P2Y1 receptor function

A_2A adenosine receptor (A_2AR), P2Y₁ receptor (P2Y₁R) and P2Y₁₂ receptor (P2Y₁₂R) are predominantly expressed on human platelets. The individual role of each of these receptors in platelet aggregation has been actively reported. Previously, hetero-oligomerization between these three receptors has been shown to occur. Here, we show that Ca²⁺ signaling evoked by the P2Y₁R agonist, 2-methylthioladenosine 5’ diphosphate (2MeSADP) was significantly inhibited by the A_2AR antagonist (ZM241385 and SCH442416) and the P2Y₁₂R antagonist (ARC69931MX) using HEK293T cells expressing the three receptors. It was confirmed that inhibition of P2Y₁R signaling by A_2AR and P2Y₁₂R antagonists was indeed mediated through A_2AR and P2Y₁₂R using 1321N1 human astrocytoma cells which do not express P2Y receptors. We expect that intermolecular signal transduction and specific conformational changes occur among components of hetero-oligomers formed by these three receptors.     

Functional subunit structure of photosystem 1 reaction center in Synechococcus sp

Photochemical activities of six different P700-chlorophyll a-proteins (CP1-a, -b₁, -b₂, -c, -d, and -e) separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis from digitonin particles of a thermophilic cyanobacterium Synechococcus sp. were examined. CP1-a, -b₁, -b₂, and -c contain the competent reaction center of photosystem 1: They were highly active in photooxidation of cytochrome c-553, the physiological electron donor to P700 in the organism, with methyl viologen as electron acceptor and showed flash-induced absorption changes indicating the charge separation between P700 and the secondary electron acceptors, P430 and A₂. The cytochrome photooxidation and P430 and A₂ photoresponses were significantly suppressed in CP1-d. CP1-e which lacks P430 and A₂ was least active in the cytochrome photooxidation. A₁, the primary electron acceptor of P700, is present in CP1-e as well as in other CP1 complexes. Comparison of the results with the polypeptide composition of CP1 complexes (Y. Takahashi, H. Koike, and S. Katoh, 1982, Arch. Biochem. Biophys.219, 209–218). indicates that CP1-c which contains four polypeptides with molecular weights of 62,000, 60,000, 14,000, and 10,000 represents the functional core of the photosystem 1 reaction center. P700, A₁, and antenna chlorophyll are associated with 62,000- and 60,000-dalton polypeptides, whereas 14,000- and 10,000-dalton polypeptides are assumed to carry P430 and A₂. The 13,000-dalton polypeptide which is associated with CP1-a, -b₁, and -b₂ is not required for the functioning of the reaction center.     

Theoretical characterization on photoelectric properties of benzothiadiazole- and fluorene-based small molecule acceptor materials for the organic photovoltaics

The upper efficiency of heterojunction organic photovoltaics depends on the increased open-circuit voltage (V _oc) and short-circuit current (J _sc). So, a higher lowest unoccupied molecular orbital (LUMO) level is necessary for organic acceptor material to possess higher V _oc and more photons absorbsorption in the solar spectrum is needed for larger J _sc. In this article, we theoretically designed some small molecule acceptors (2～5) based on fluorene (F), benzothiadiazole, and cyano group (CN) referring to the reported acceptor material 2-[{7-(9,9-di-n-propyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazol-4-yl}methylene]malononitrile (1), the crucial parameters affecting photoelectrical properties of compounds 2～5 were evaluated by the density functional theory (DFT) and time dependent density functional theory (TDDFT) methods. The results reveal that compared with 1, 3 and 4 could have the better complementary absorption spectra with P3HT, the increased LUMO level, the improved V _oc, and the decreased electronic organization energy (λ _e). From the simulation of transition density matrix, it is very clear that the excitons of molecules 3 and 4 are easier to separate in the material surface. Therefore, 3 and 4 may become potential acceptor candidates for organic photovoltaic cells. In addition, with the increased number of CN, the optoelectronic properties of the molecules show a regular change, mainly improve the LUMO level, energy gap, V _oc, and absorption intensity. In summary, reasonably adjusting CN can effectively improve the photovoltaic properties of small molecule acceptors.

Open image in new window

Graphical Abstract Structure–property relationship of small molecule acceptors could be rationally evaluated in the article. The changes of conjugate length and CN are important strategies to alter the photovoltaic properties of small molecule acceptors. Therefore, taking the K12/1 as a reference, we have theoretically designed a series of small molecule acceptors (2–4). The calculated results by means of DFT and TDDFT manifest that molecules 3 and 4 have the better complementary absorption spectra with P3HT, the increased LUMO level, the improved V _oc, the decreased electronic organization energy and the easier separation in the material surface than 1. In summary, reasonably increasing conjugate length and decreasing CN can effectively improve the PCE, which will provide a theoretical guideline for the design and synthesis of new small molecule acceptors.

     

Trade‐Off between Trap Filling,Trap Creation,and Charge Recombination Results in Performance Increase at Ultralow Doping Levels in Bulk Heterojunction Solar Cells

Doping of organic bulk heterojunction solar cells has the potential to improve their power conversion efficiency (PCE). Deconvoluting the effect of doping on charge transport, recombination, and energetic disorder remains challenging. It is demonstrated that molecular doping has two competing effects: on one hand, dopant ions create additional traps while on the other hand free dopant‐induced charges fill deep states possibly leading to V _OC and mobility increases. It is shown that molar dopant concentrations as low as a few parts per million can improve the PCE of organic bulk heterojunctions. Higher concentrations degrade the performance of the cells. In doped cells where PCE is observed to increase, such improvement cannot be attributed to better charge transport. Instead, the V _OC increase in unannealed P3HT:PCBM cells upon doping is indeed due to trap filling, while for annealed P3HT:PCBM cells the change in V _OC is related to morphology changes and dopant segregation. In PCDTBT:PC70BM cells, the enhanced PCE upon doping is explained by changes in the thickness of the active layer. This study highlights the complexity of bulk doping in organic solar cells due to the generally low doping efficiency and the constraint on doping concentrations to avoid carrier recombination and adverse morphology changes.     

Intracellular peptidoglycan hydrolases of the bacterium Xanthomonas campestris XL-1

A system of intracellular peptidoglycan hydrolases of Xanthomonas campestris XL-1 comprises about 10 enzymes of different localization and substrate specificity. Seven enzymes (A₁-A₇) are localized in cytosol, one enzyme (A₈) in periplasm, and two enzymes (A₉, A₁₀) were found in the fraction of cell walls and membranes. While the culture is entering the logarithmic growth stage from the stationary stage, a change occurs in the activity of the cytosolic enzymes: A₁ significantly increases, and A₅ and A₆ decrease. The spectrum of cytosolic enzymes also depends on the growth medium composition. The enzyme A₇ present in cells secreting extracellular enzymes (medium 5/5) was not found in non-secreting cells (LB medium). Unlike extracellular enzymes, intracellular peptidoglycan hydrolases are primarily acidic proteins. The data indicate that the system of intracellular peptidoglycan hydrolases of X. campestris is under complex and strict regulation.     

Simultaneous Enhancement of Three Parameters of P3HT‐Based Organic Solar Cells with One Oxygen Atom

Poly(3‐hexylthiophene) (P3HT)‐based organic solar cells (OSCs) have attracted much attention due to their advantages of low‐cost production and matured roll‐to‐roll manufacture. However, the efficiency of P3HT‐based OSCs lag much behind the non‐P3HT ones due to their negligible absorption of long wavelengths of light over 650 nm, high‐lying highest occupied molecular orbitals (HOMO), and difficulty of controlling morphology. In this study, the alkyl chains of the nonfullerene acceptors are replaced with alkoxy chains to achieve synergistic enhancement of all three parameters ( short circuit current density (J_SC), open circuit voltage (V_OC), and fill factor (FF)) and thus significant increase of power conversion efficiency for P3HT‐based OSCs. As a result, the OSCs exhibit a maxima efficiency of 6.6%. The P3HT‐based systems are systematically studied with optical spectroscopy, photoluminescence, cyclic voltametry, space charge limit current, grazing incident wide‐angle X‐ray scattering, transient absorption spectroscopy, transmission electron microscope, and atomic force microscopy to probe the mechanism, which reveal that introducing alkoxy chains simultaneously increases the energy levels of the HOMO and the lowest unoccupied molecular orbitals, enhances the light absorption, improves the rigidity of the backbone and charge transport mobility, and tunes the molecular orientation and film morphology, thus improving the photovoltaic performance. This contribution provides an important guidance in the design of novel nonfullerene acceptors for high‐performance P3HT‐based OSCs.