A2 Unit Research Articles

Wide bandgap polymer donors with an acceptor1-π-acceptor2-π configuration for efficient polymer solar cells

To maximize the photovoltaic performance of polymer solar cells (PSCs), polymer donors and nonfullerene acceptors (NFAs) should be designed with complementarily optical and electronic properties as well as desirable morphological features. Currently, high-performance polymer donors are mainly constructed by alternating copolymerization of electron-rich (D) and electron-deficient (A) units. Here, we demonstrate that acceptor1-π-acceptor2-π (A1-π-A2-π)-type polymer donors constructed by copolymerization of two different A units can achieve comparable photovoltaic properties with those of D-π-A-π-type counterparts. By using the ladder-type 4,10-bis(2-hexyldecyl)-thieno[2ˊ,3ˊ:5,6]pyrido[3,4-g]thieno-[3,2-c]isoquinoline-5,11-dione as A1 unit, difluorobenzotriazole or benzodithiophene-4,8-dione as A2 unit, and thiophene unit as the π bridge, two A1-π-A2-π-type copolymers, P03 and P07, are successfully synthesized. Due to the weakened intramolecular charge-transfer effect, P03 and P07 exhibit wide bandgaps of 1.88 and 1.74 eV, respectively. In combination with the NFA of L8-BO, the P03:L8-BO-based blend shows superior crystallinity and uniform phase-separated morphology thereby leading to a higher power conversion efficiency (PCE) of 15.03 % in comparison with the P07:L8-BO-based blend which shows a PCE of 9.84 %. Notably, the 15.03 % efficiency is by far the highest value for PSCs based on A1-π-A2-π-type polymer donors. These results provide useful guidance for the future design of high-performance donor copolymers for PSCs.

Determination of the relationship between the Vocational Qualifications and Academic Programs on a Perceived Competencies Basis Approach: A Case for Geographical Information Systems

GIS education and training activities become widespread as GIS utilization inevitably increases worldwide. Besides, vocational standards and qualifications are developed to form a quality assurance basis for GIS-related jobs and services and the employment of qualified personnel. From this perspective, this study aims to examine to what level the graduates of GIS associate degree, master, and doctorate programs have gained the necessary knowledge and competencies defined in the GIS Specialist (Level 6) National Qualification throughout their academic education. Within this context, an online survey was developed based on 43 performance criteria derived from the vocational qualification units (A1, A2, A3). The respondents were asked to self-evaluate the achievement of the given criteria during their academic education on a 5-point Likert scale. It was detected that 39.1% of the 174 survey participants have associate degrees, 61.7% have master's degrees (with thesis, without thesis, and distance education), and 6.9% have doctorate degrees. In comparison, 3% of them completed the GIS certificate program. The results showed that the competency achievement perceptions in the A3 section increased following the education level of the graduates. No significant difference was determined for A1, while an insignificant difference was detected for the A2 unit between the graduates of doctorate and distance education master's degree programs. The results are expected to be adopted by the relevant parties to align the GIS education programs with the sectoral needs and vocational qualifications.

Benzotriazole-based asymmetric nonfullerene acceptors with A-D-A1-A2 type structure for organic solar cells

Although the wide-bandgap benzotriazole (BTA)-based A2-A1-D-A1-A2 type nonfullerene acceptors (NFAs) have realized super-high open-circuit voltage (VOC) of 1.3 V, the short-circuit current density (JSC) of these materials lag behind the narrow-bandgap A-D-A type analogs. Here, we design and synthesize two asymmetric A-D-A1-A2 type molecules, A301 and A302, by adopting 1,1-dicyanomethylene-3-indanone (IC), BTA and 2-(1,1-dicyanomethylene)rhodanine (RCN) as A, A1 and A2 units, respectively. Under the synergistic regulation of asymmetric end groups and side chain engineering, A302 with alkyl side chains on D unit exhibits red-shifted absorption, tighter molecular packing, and stronger crystallinity in comparison with A301 with phenyl side chain. Consequently, PM6:A302-based organic solar cells (OSCs) realize an enhanced efficiency of 11.09% with an improved JSC of 17.95 mA cm−2, compared to those of PM6:A301-based device (PCE = 8.18%, JSC = 14.57 mA cm−2). Notably, the JSC of 17.95 mA cm−2 is the highest value for BTA-based NFAs to date. This work demonstrates A-D-A1-A2 type NFAs have great potential to balance the JSC and VOC, and side chain on D unit also has a great impact on the properties of this kind of materials.

Composition-Tolerant Terpolymers for Efficient, Nonhalogenated Solvent-Processed Polymer Solar Cells

The design of terpolymers is a compelling strategy to improve the polymer solar cell (PSC) performance. However, the terpolymer composition at which the power conversion efficiency (PCE) of associated PSCs is typically optimized generally falls within a very narrow range, complicating the reproducible fabrication of optimal PSCs. In this study, a series of D–A1–D–A2 type random terpolymers (DTTz-X, where X = 10–60) is designed with structurally similar A1 and A2 accepting units. The sulfur atom of the benzothiadiazole subunit in the A1 (DTBT) unit is replaced by a nitrogen atom in the A2 (DTTz) unit, enabling the introduction of an alkyl solubilizing group while maintaining the overall structural properties of the terpolymer system. Consequently, the DTTz-X PDs maintain good optoelectronic properties at various A1/A2 ratios, while their processability in nonhalogenated solvents is significantly enhanced. Accordingly, the PSC performance of the terpolymer system shows good composition tolerance; i.e., the terpolymer system affords PSCs with PCEs exceeding 15% (up to 16.4%) over a broad range of DTTz compositions (10–40 mol %). This study establishes a useful design strategy for the development of efficient terpolymer donors for reproducible and eco-friendly fabrication of high-performance PSCs.

Terpolymer Donor with Inside Alkyl Substituents on Thiophene π-Bridges toward Thiazolothiazole A2 -Unit Enables 18.21% Efficiency of Polymer Solar Cells.

PM6 is a widely used D-A copolymer donor in the polymer solar cells (PSCs). Incorporating second electron-withdrawing (A2 ) units into PM6 backbone by ternary D-A1 -D-A2 random copolymerization strategy is an effective approach to further improve its photovoltaic performance. Here, the authors synthesize the PM6-based terpolymers by introducing thiazolothiazole as the A2 units connecting with thiophene π-bridges attaching alkyl substituent towards the A2 unit (PMT-CT) or towards D-unit (PMT-FT), and study the effect of the alkyl substituent position on the photovoltaic performance of them. Two terpolymers PMT-FT-10 and PMT-CT-10 are obtained by incorporating 10% A2 units in the terpolymers. The film of PMT-CT-10 shows slightly up-shifted highest occupied molecular orbital (HOMO) energy levels while better co-planar structure than that of PMT-FT-10. Meanwhile, the PMT-CT-10:Y6 blend film exhibits better molecular packing properties, more proper phase separation and more balanced hole and electron mobilities, which are beneficial to more efficient exciton dissociation, efficient charge transport and weaker bimolecular recombination. Consequently, the PMT-CT-10 based PSCs obtain the highest power conversion efficiency of 18.21%. The results indicate that side chain position on the thiophene π-bridges influence the device performance of the terpolymer donors, and PMT-CT-10 is a high efficiency polymer donor for the PSCs.

Designing and theoretical characterization of D-π-A1-π-A2 typed organic small molecule donor materials

A few of novel D-π-A1-π-A2 typed asymmetric organic small molecules (OSMs) named BT-CN, BT-P, BT-P-2F and BT-P-2F–CN were designed theoretically, by a 1,3-indanone (IDO) substitution, independent and synergistic modification of malononitrile group and F atoms on the A2 unit of the reported BT-2 structure, which is based on triphenylamine (TPA) as electron-donating group, 5,6-difluoro-2,1,3-benzothiadiazole (FFBT) as electron-withdrawing core. The molecular structures, frontier molecular orbitals, UV–vis absorption spectra, atomic charges, energy loss (Eloss) and charge transfer properties of these OSMs were calculated by quantum chemistry method. The effects of terminal substitution and modification on the molecular structure and photovoltaic properties were further explored. As a result, in contrast to BT-2 (A2 = 3-hexyl rhodamine), BT-P (A2 = 1, 3- indene diketone) has the same band gap (Eg) and highest occupied molecular orbital (HOMO) level, but better planarity and charge transfer properties; Compared to BT-2 and BT-P, BT-CN and BT-P-2F not only achieve more narrowed Eg values and deeper HOMO levels, but also get better charge transfer properties via independent modification with malononitrile group and F atoms; Notably, BT-P-2F–CN has the most narrowed Eg, the lowest deep-lying HOMO, the best charge transfer properties and smallest Eloss, due to synergistic effects of malononitrile group and F atoms. The power conversion efficiencies (PCEs) of 5.0%, 5.8% and 8.3% have been performed by the photovoltaic devices for BT-P-2F/PC61BM, BT-CN/PC61BM and BT-P-2F–CN/PC61BM systems, respectively, based on Scharber models. On the basis of the results, BT-P-2F, BT-CN and BT-P-2F–CN would be proposed as potential high performance donor materials of asymmetric OSMs based on TPA-BT backbone. This study could provide a useful theoretical guide for molecular design for high performance organic solar cells.

New Medium Bandgap Donor D-A1 -D-A2 Type Copolymers Based on Anthra[1,2-b: 4,3-b":6,7-c"'] Trithiophene-8,12-dione Groups for High-Efficient Non-Fullerene Polymer Solar Cells.

A new acceptor unit anthra[1,2-b: 4,3-b': 6,7-c'']trithiophene-8,12-dione (А3Т) (A2) is synthesized and used to design D-A1 -D-A2 medium bandgap donor copolymers with same thiophene (D) and A2 units but different A1, i.e., fluorinated benzothiadiazole (F-BTz) and benzothiadiazole (BTz) denoted as P130 and P131, respectively. Their detailed optical and electrochemical properties are examined. The copolymers show good solubility in common organic solvents, broad absorption in the visible spectral region from 300 to 700 nm, and deeper HOMO levels of -5.45 and -5.34 eV for P130 and P131, respectively. Finally, an optimized polymer solar cell (PSC) based on P131 as the donor and narrow bandgap non-fullerene small molecule acceptor Y6 demonstrated a power conversion efficiency (PCE) of >11.13%. To further improve the efficiency of the non-fullerene PSC, the P130 is optimized by introducing a fluorine atom into the BTz unit, F-BTz acceptor unit, and PCE PSC based on P130: Y6 active layer increased to >15.28%, which is higher than that for the non-fluorinated analog P131:Y6. The increase in the PCE for former PSC is attributed to the more crystalline nature and compact π-π stacking distance, leading to more balanced charge transport and reduced charge recombination. These remarkable results demonstrate that A3T-based copolymer P130 with F-BTz as the second acceptor is a promising donor material for high-performance PSCs.

Study on the side chain effect of A2-A1-D-A1-A2 type non-fullerene acceptors matched with P3HT

Because of the advantages of low cost, stability and easy synthesis, poly(3-hexylthiophene) (P3HT) was the most classic photovoltaic polymer and promoted the rapid progress of fullerene-based organic solar cells (OSCs) during 2005–2015. In comparison with A-D-A type non-fullerene acceptors (NFAs), A2-A1-D-A1-A2 type molecules can realize higher open-circuit voltage (VOC) and also match well with P3HT. Hence, here we modified the classic A2-A1-D-A1-A2 type NFA of BTA3 by altering the side chains at three different positions, and synthesized five new materials of BTA3b-3f to investigate the structure-properties relationship. By fine-tuning the side chains at middle D unit, BTA3b, BTA3c and BTA3d show totally different power conversion efficiencies (PCEs) of 5.95, 3.80 and 4.74% respectively, which demonstrate the modification of D unit can significantly influence the intermolecular interaction. On the other hand, with the modulation of side chains at A1 and A2 units, BTA3e and BTA3f show relatively high PCEs of 5.48 and 6.15% respectively. Our results indicate the systematical side chain engineering for A2-A1-D-A1-A2 type NFAs play a vital role to improve the photovoltaic performance of P3HT-based OSCs.

Unfused-ring small molecule acceptors based on A1-D-A2-D-A1 architecture with low non-radiative energy loss and excellent air stability

Organic solar cells (OSCs) have made enormous progress in recent years. However, OSCs still suffer from the low price–quality ratio since the complex synthesis of photovoltaic materials and the poor stability of the devices. Comparing with traditional large conjugated ladder-type non-fullerene acceptors, the unfused-ring acceptors with non-covalent intramolecular interactions could notably simplify the synthetic routes while maintaining the device performance. Here, we designed and synthesized two A1-D-A2-D-A1 type non-fullerene acceptors named BDTC-F and BDTC-Cl based on 1,3-bis(4-(2-ethylhexyl)-thiophen-2-yl)-5,7-bis(2-ethylhexyl)-benzo[1,2-c:4,5c']dithiophene-4,8-dione (BDD) as A2 unit. With cyclopenta[2,1-b:3,4-b']dithiophene functions as the D unit, the weak O⋯S interaction between A2 and D units is formed, which reduces the torsion angle between them and increases the planarity of the molecular backbone. Furthermore, the participation of BDD could deepen the energy levels of these two acceptors, makes it possible to decrease the energy loss of the corresponding devices. When blending with polymer donor PM6, devices based on both acceptors exhibit PCEs over 10% with low energy losses of 0.59 and 0.57 eV for BDTC-F and BDTC-Cl, respectively. Moreover, the devices based on PM6:BDTC-F and PM6:BDTC-Cl demonstrate excellent air stability. After stored in the ambient atmosphere without encapsulation for 1,200 h, devices based on these two acceptors retained over 96% of their initial PCEs. These results demonstrate that designing the A1-D-A2-D-A1 type acceptor with non-covalent intramolecular interactions is an effective strategy to construct low-cost and air-stable OSCs.

Tuning the electrochemical and optical properties of donor-acceptor D-A2-A1-A2-D derivatives with central benzothiadiazole core by changing the A2 strength

Two molecules named QXBT and BXBT with donor-acceptor D-A2-A1-A2-D type of structure were synthesized and characterized by means of electrochemical (Cyclic and Differential Pulse Voltammetry), spectroscopic and spectroelectrochemical (UV–Vis-NIR, Fluorescence and Electron Paramagnetic Resonance) techniques in order to evaluate the impact of different A2 acceptors on properties of such compounds with benzothiadiazole as A1 central core and alkylthiophene donor moieties. In the case of QXBT, the quinoxaline and in the BXBT molecule the benzoxadiazole serves as a A2 unit. The investigations have revealed that changing the A2 allows to tune the conjugation of molecules and affects not only reduction but oxidation process as well.

Random Polymerization Strategy Leads to a Family of Donor Polymers Enabling Well-Controlled Morphology and Multiple Cases of High-Performance Organic Solar Cells.

Developing high-performance donor polymers is important for nonfullerene organic solar cells (NF-OSCs), as state-of-the-art nonfullerene acceptors can only perform well if they are coupled with a matching donor with suitable energy levels. However, there are very limited choices of donor polymers for NF-OSCs, and the most commonly used ones are polymers named PM6 and PM7, which suffer from several problems. First, the performance of these polymers (particularly PM7) relies on precise control of their molecular weights. Also, their optimal morphology is extremely sensitive to any structural modification. In this work, a family of donor polymers is developed based on a random polymerization strategy. These polymers can achieve well-controlled morphology and high-performance with a variety of chemical structures and molecular weights. The polymer donors are D-A1-D-A2-type random copolymers in which the D and A1 units are monomers originating from PM6 or PM7, while the A2 unit comprises an electron-deficient core flanked by two thiophene rings with branched alkyl chains. Consequently, multiple cases of highly efficient NF-OSCs are achieved with efficiencies between 16.0% and 17.1%. As the electron-deficient cores can be changed to many other structural units, the strategy can easily expand the choices of high-performance donor polymers for NF-OSCs.

Tuning the intermolecular interaction of A2-A1-D-A1-A2 type non-fullerene acceptors by substituent engineering for organic solar cells with ultrahigh VOC of ~1.2 V

For non-fullerene acceptors (NFAs) with linear A2-A1-D-A1-A2 backbone, there are three kinds of possible intermolecular interaction, A1-A1, A1-A2 and A2-A2 stacking. Hence, it is a huge challenge to control this interaction and investigate the effect of intermolecular stacking model on the photovoltaic performance. Here, we adopt a feasible strategy, by utilizing different substituent groups on terminal A2 unit of dicyanomethylene rhodanine (RCN), to modulate this stacking model. According to theoretical calculation results, the molecule BTA3 with ethyl substituent packs via heterogeneous interaction between A2 and A1 unit in neighboring molecules. Surprisingly, the benzyl group can effectively transform the aggregation of BTA5 into homogeneous packing of A2-A2 model, which might be driven by the strong interaction between benzyl and A1 (benzotriazole) unit. However, different with benzyl, phenyl end group impedes the intermolecular interaction of BTA4 due to the large steric hindrance. When using a BTA-based D-π-A polymer J52-F as donor according to “Same-A-Strategy”, BTA3-5 could achieve ultrahigh open-circuit voltage (VOC) of 1.17–1.21 V. Finally, BTA5 with benzyl groups realized an improved power conversion efficiency (PCE) of 11.27%, obviously higher than that of BTA3 (PCE=9.04%) and BTA4 (PCE=5.61%). It is also worth noting that the same trend can be found when using other four classic p-type polymers of P3HT, PTB7, PTB7-Th and PBDB-T. This work not only investigates the intermolecular interaction of A2-A1-D-A1-A2 type NFAs for the first time, but also provides a straightforward and universal method to change the interaction model and improve the photovoltaic performance.

Electron-Deficient and Quinoid Central Unit Engineering for Unfused Ring-Based A1 -D-A2 -D-A1 -Type Acceptor Enables High Performance Nonfullerene Polymer Solar Cells with High Voc and PCE Simultaneously.

Here, a pair of A1 -D-A2 -D-A1 unfused ring core-based nonfullerene small molecule acceptors (NF-SMAs), BO2FIDT-4Cl and BT2FIDT-4Cl is synthesized, which possess the same terminals (A1 ) and indacenodithiophene unit (D), coupling with different fluorinated electron-deficient central unit (difluorobenzoxadiazole or difluorobenzothiadiazole) (A2 ). BT2FIDT-4Cl exhibits a slightly smaller optical bandgap of 1.56 eV, upshifted highest occupied molecular orbital energy levels, much higher electron mobility, and slightly enhanced molecular packing order in neat thin films than that of BO2FIDT-4Cl. The polymer solar cells (PSCs) based on BT2FIDT-4Cl:PM7 yield the best power conversion efficiency (PCE) of 12.5% with a Voc of 0.97 V, which is higher than that of BO2FIDT-4Cl-based devices (PCE of 10.4%). The results demonstrate that the subtle modification of A2 unit would result in lower trap-assisted recombination, more favorable morphology features, and more balanced electron and hole mobility in the PM7:BT2FIDT-4Cl blend films. It is worth mentioning that the PCE of 12.5% is the highest value in nonfused ring NF-SMA-based binary PSCs with high Voc over 0.90 V. These results suggest that appropriate modulation of the quinoid electron-deficient central unit is an effective approach to construct highly efficient unfused ring NF-SMAs to boost PCE and Voc simultaneously.

A2-D-A1-D-A2-type small molecule acceptors incorporated with electron-deficient core for non-fullerene organic solar cells

Two A2-D-A1-D-A2-type small molecule acceptors (SMAs), DFB-dIDT and BT-dIDT with 2,5-difluorobenzene (DFB) or benzothiadiazole (BT) as electron-withdrawing core (A1) and a derivative of indanone as A2 units, were prepared for applications in organic solar cells (OSCs). The results indicate that BT unit is more beneficial to forming multiple noncovalent conformational locks of N⋯S and N⋯H between BT and IDT unit than DFB in the core, so BT-dIDT showed better molecular coplanarity, higher-lying HOMO energy level, more red-shifted spectrum, superior molar absorption coefficient (1.60 × 105 M−1 cm−1 at 696 nm), more complementary absorption spectrum with PBDB-T and better photovoltaic performance than DFB-dIDT. As a result, the BT-dIDT-based OSCs blending with PBDB-T exhibited higher power conversion efficiency (PCE) value of 10.52% with higher Jsc of 18.59 mA cm−2 than that of the DFB-dIDT-based devices (PCE of 6.71% with Jsc of 15.58 mA cm−2). These results demonstrate that the A2-D-A1-D-A2-type SMAs incorporated with a suitable electron-deficient core are promising candidates for high performance OSCs.

Low-bandgap D-A1-D-A2 type copolymers based on TPTI unit for efficient fullerene and nonfullerene polymer solar cells

To obtain low-bandgap polymers paired well with fullerene and nonfullerene acceptors, here we adopted a D-A1-D-A2 motif to develop two new low-bandgap copolymers PTPTI-T-BDD and PTPTI-T-FBT, where thiophene was used as the D unit, thieno[2′,3′:5,6]pyrido[3,4-g]thieno[3,2-c]-isoquinoline-5,11(4H,10H)-dione (TPTI) was used as the A1 unit, and benzo[1,2-b:4,5-c′]dithiophene-4,8-dione (BDD) and 5,6-difluoro-2,1,3-benzothiadiazole (FBT) were employed as the A2 unit, respectively. Effects of the electron-withdrawing strength of A2 unit on optoelectronic and photovoltaic properties of the PTPTI-T-BDD- and PTPTI-T-FBT-based fullerene and nonfullerene polymer solar cells (PSCs) were systematically investigated. When blended with PC71BM and ITIC, PTPTI-T-FBT-based PSCs showed a power conversion efficiency (PCE) of 6.20% and 6.03%, respectively, both of which are higher than that of PTPTI-T-BDD-based PSCs. Furthermore, ternary PSCs based on PBDB-T:PTPTI-T-FBT:PC71BM exhibited an improved PCE of 7.92%. This work suggests that constructing D-A1-D-A2 copolymers is a promising strategy to develop low-bandgap copolymers for efficient fullerene and nonfullerene PSCs with a reduced energy loss.

Synthesis and photovoltaic properties of small molecule electron acceptors with twin spiro-type core structure

In this work, we have developed two A1-A2-D-A2-A1 type small molecule electron acceptors (DTFBT-1, DTFBT-2) with twin spiro-type core structure as D unit, benzothiadiazole (BT) as A2 unit, 3-ethyl-rhodanine (R) or 2-(1,1-Dicyanomethylene) rhodanine (RCN) as A1 unit. The organic solar cells (OSCs) based on the acceptors DTFBT-1 or DTFBT-2 blended with donor J71 achieved the power conversion efficiency (PCE) of 3.35% and 4.40%, respectively. The twin spiro-type core structure with a good planarity facilitates the stacking of molecules. Especially, DTFBT-1 and DTFBT-2 based devices exhibited a high Voc of 1.15 V and 0.96 V for as-cast film due to the high LUMO of acceptors. DTFBT-2 based device showed a bigger short circuit current density (Jsc) due to the RCN of excellent electron-accepting ability. The results indicate that twin spiro-type core fused side group and the terminal group end-capped are significant strategies to improve the performance of nonfullerene acceptors (NFA) devices.

Double Acceptor Block-Containing Copolymers with Deep HOMO Levels for Organic Solar Cells: Adjusting Carboxylate Substituent Position for Planarity.

A deep highest occupied molecular orbital (HOMO) level is a prerequisite for polymer donor material to boost the organic solar cells (OSCs) performance by achieving high open circuit voltage ( Voc). Abandoning the traditional concept of donor-acceptor (D-A) structure, two copolymers PBTZ-4TC and PBTZ-C4T based on acceptor1-π-acceptor2 (A1-π-A2) architecture, where thiophene as the bridge, the difluorinated benzotriazole (BTZ) as A1 unit alternating copolymerized with 4,4'-dicarboxylate-substituted difluorotetrathiophene (4TC) and 3,3'-dicarboxylate-substituted difluorotetrathiophene (C4T) as A2, respectively, are developed. Because of the double acceptor blocks with high electron affinity, both A1-π-A2 type copolymers possess the lower HOMO levels of 5.52-5.56 eV, which are lower than most D-A type donors. Polymer PBTZ-4TC and PBTZ-C4T have the same backbone but only differ with the position of carboxylate substituent on the A2 unit. Intriguingly, subtle optimizing the position of the carboxylate-substitute causes a significantly difference on the properties of the A1-π-A2 type copolymers. PBTZ-C4T with more planar geometry is demonstrated with better light absorption, higher crystallinity, more pronounced temperature-dependent aggregation effect, and favorable bulk heterojunction morphology but with slightly higher HOMO level and more emission energy loss relative to the PBTZ-4TC. The PBTZ-C4T device exhibits the higher power conversion efficiency (PCE) of 9.34% than the PBTZ-4TC-based one (8.75%). These results reveal that concept of A1-π-A2 type copolymers not only can afford more flexibility in tuning the energy levels to achieve the deep HOMO levels but also can provide a facial strategy to greatly enrich the types of polymer donors for high-performance OSCs.

Controlling the Cyano‐Containing A2 Segments in A2‐A1‐D‐A1‐A2 Type Non‐Fullerene Acceptors to Combine with a Benzotriazole‐Based p‐Type Polymer: “Same‐Acceptor‐Strategy” for High VOC Organic Solar Cells

To achieve efficient organic solar cells (OSCs), the design of promising non‐fullerene small molecular acceptors (SMAs) is crucially important and the relationship between the chemical structure and optoelectronic properties needs to be further investigated. Herein, an A2‐A1‐D‐A1‐A2 molecular skeleton is adopted to study the effect of end‐capped A2 groups containing different numbers of cyano units, where D and A1 are fixed as indacenodithiophene (IDT) and benzotriazole (BTA) units, respectively. Utilizing the “same‐acceptor‐strategy,” three BTA‐based SMAs, named as BTA701, BTA3, and BTA703, are paired with a BTA‐based p‐type polymer J71. The open‐circuit voltage (VOC) gradually decreases with the enhancement of electron‐accepting ability of terminal A2 units, from 1.32 V (BTA701) to 1.20 V (BTA3) and to 0.85 V (BTA703). The device J71:BTA3 eventually shows the best power conversion efficiency (PCE) of 8.60% with a VOC up to 1.2 V because of the complementary light absorption, high and balanced hole and electron mobility, suitable phase separation, and crystallinity. This study indicates that appropriate cyano‐containing units in BTA‐based SMAs can effectively modulate the absorption, energy levels, charge mobility and surface free energy, which can provide valuable insights to the further design of SMAs. In addition, these results prove that the “same‐acceptor‐strategy” is simple and effective to realize a VOC as high as 1.2V.

Combining DNA-stabilized silver nanocluster synthesis with exonuclease III amplification allows label-free detection of coralyne

In this paper we describe a label-free biosensor for coralyne, prepared by combining DNA-stabilized silver nanoclusters (Ag NCs) with an exonuclease III amplification strategy. An artificial DNA probe having a polyadenine (poly-A) sequence at both the 3′- and 5′-ends was used as a probe to detect coralyne. In the absence of coralyne, the probe existed in a hairpin conformation that left both its 3′- and 5′-ends free. In the presence of coralyne, two adjacent adenine (A) bases in the poly-A sequence of the probe formed an A2 unit and then coordinated with coralyne through non-Watson–Crick base pairing. The DNA probe, having captured coralyne, was subsequently digested by exonuclease III, even though the distance between the A2 units in the A2–coralyne–A2 complex would be much larger than that found in common Watson–Crick base pairing. After digestion, the DNA probe became a single-stranded DNA (ssDNA) residue and released its captured coralyne. The liberated coralyne was then coordinated by another DNA probe having the hairpin conformation; as a result, many ssDNA residues formed after digestion. Two kinds of Ag NCs having different optical utilities were obtained: one corresponding to the hairpin conformational DNA probe and the other to the ssDNA residue. The difference in fluorescence intensity at 588 nm of these two kinds of Ag NCs reflected the concentration of coralyne. The linear range (on a logarithmic scale) for detecting coralyne spanned from 5 to 1000 nM, with an estimated detection limit of 1.83 nM.

New insights on the age of the post-Urgonian marly cover of the Apt region (Vaucluse, SE France) and its implications on the demise of the North Provence carbonate platform

Our contribution presents an integrated litho-, bio- and chemostratigraphic study of the best-preserved outcrops of the post-Urgonian marly cover (A1 unit) of the North Provence carbonate platform. The study of the rich ammonite fauna from the Apt–Gargas area (SE Vaucluse) confirms that the A1 unit is older than previously assumed and dated to the upper (but non-uppermost) part of the lower Aptian Deshayesites forbesi Zone of the Mediterranean standard zonation. This interval is assigned to the lower part of the Roloboceras hambrovi Subzone as defined in the present contribution which is time equivalent to the spreading of the OAE 1a. Microfossil occurrences previously documented in the A1 unit are consistent with our ammonite-age calibration. Unfortunately, the curves of the carbon and oxygen stable isotopes exhibit a correlative signal probably caused by an early diagenetic overprint which questions the previous use of the C-isotope signal for precise chronostratigraphic correlation with respect to the OAE 1a excursion. The top of the A1 unit is marked by a burrowed firmground locally infilled and capped by glauconite-rich sandy marls which grade into the blue–grey muddy marls of the overlying A2 unit. The hiatus associated to this discontinuity is equivalent to the culmination of the OAE 1a, including the uppermost D. forbesi Zone (=upper R. hambrovi Subzone as herein defined) and the lower D. deshayesi Zone. The revised calibration of the post-Urgonian marl implies that the ammonite-age calibration of the North Provence carbonate platform should be revised and questions the timing and driving mechanisms of its stepwise demise.