Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

A new polymer donor (PBDB-T-SF) and a new small molecule acceptor (IT-4F) for fullerene-free organic solar cells (OSCs) were designed and synthesized The influences of fluorination on the absorption spectra, molecular energy levels, and charge mobilities of the donor and acceptor were systematically studied The PBDB-T-SF:IT-4F-based OSC device showed a record high efficiency of 131%, and an efficiency of over 12% can be obtained with a thickness of 100–200 nm, suggesting the promise of fullerene-free OSCs in practical applications

Molecular Optimization Enables over 13% Efficiency in Organic Solar Cells

Recent Advances in Bulk Heterojunction Polymer Solar Cells

18% Efficiency organic solar cells

Organic solar cells (OSCs) have been dominated by donor:acceptor blends based on fullerene acceptors for over two decades. This situation has changed recently, with non-fullerene (NF) OSCs developing very quickly. The power conversion efficiencies of NF OSCs have now reached a value of over 13%, which is higher than the best fullerene-based OSCs. NF acceptors show great tunability in absorption spectra and electron energy levels, providing a wide range of new opportunities. The coexistence of low voltage losses and high current generation indicates that new regimes of device physics and photophysics are reached in these systems. This Review highlights these opportunities made possible by NF acceptors, and also discuss the challenges facing the development of NF OSCs for practical applications.

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Organic solar cells based on non-fullerene acceptors.

Two conjugated donor polymers (PB2F-Cl and PB2F-2Cl) based on benzo[1,2-b:4,5-b′]dithiophene and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione with asymmetrical and symmetrical chlorinated thiophene-bridges were designed and synthesized. Both polymers exhibited extremely deep HOMO levels of −5.50 and −5.56 eV for PB2F-Cl and PB2F-2Cl, respectively. Although PB2F-Cl had a more planar conjugated backbone, PB2F-Cl exhibited a weaker aggregation behaviour than PB2F-2Cl in chlorobenzene solution due to its regioirregular conjugated backbone. After blending with an IT-4F acceptor, the PB2F-Cl:IT-4F film exhibited a slightly stronger lamellar stacking and a weaker π stacking compared to the PB2F-2Cl:IT-4F film as confirmed by grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. In PSCs, the power conversion efficiency (PCE) of the PB2F-Cl:IT-4F-based PSC was 10.81%, while the PCE of the PB2F-2Cl:IT-4F-based PSC reached 12.79%.

Study of photovoltaic performances for asymmetrical and symmetrical chlorinated thiophene-bridge-based conjugated polymers

https://onlinelibrary.wiley.com/doi/pdf/10.1002/sstr.202100099

Achieving 18.14% Efficiency of Ternary Organic Solar Cells with Alloyed Nonfullerene Acceptor

Background: Direct cardiac reprogramming of fibroblasts into cardiomyocytes has emerged as a promising strategy to remuscularize injured myocardium. However, it is insufficient to generate functional induced cardiomyocytes from human fibroblasts using conventional reprogramming cocktails, and the underlying molecular mechanisms are not well studied. Methods: To discover potential missing factors for human direct reprogramming, we performed transcriptomic comparison between human induced cardiomyocytes and functional cardiomyocytes. Results: We identified TBX20 (T-box transcription factor 20) as the top cardiac gene that is unable to be activated by the MGT133 reprogramming cocktail (MEF2C, GATA4, TBX5, and miR-133). TBX20 is required for normal heart development and cardiac function in adult cardiomyocytes, yet its role in cardiac reprogramming remains undefined. We show that the addition of TBX20 to the MGT133 cocktail (MGT+TBX20) promotes cardiac reprogramming and activates genes associated with cardiac contractility, maturation, and ventricular heart. Human induced cardiomyocytes produced with MGT+TBX20 demonstrated more frequent beating, calcium oscillation, and higher energy metabolism as evidenced by increased mitochondria numbers and mitochondrial respiration. Mechanistically, comprehensive transcriptomic, chromatin occupancy, and epigenomic studies revealed that TBX20 colocalizes with MGT reprogramming factors at cardiac gene enhancers associated with heart contraction, promotes chromatin binding and co-occupancy of MGT factors at these loci, and synergizes with MGT for more robust activation of target gene transcription. Conclusions: TBX20 consolidates MGT cardiac reprogramming factors to activate cardiac enhancers to promote cardiac cell fate conversion. Human induced cardiomyocytes generated with TBX20 showed enhanced cardiac function in contractility and mitochondrial respiration.

https://www.ahajournals.org/doi/pdf/10.1161/CIRCULATIONAHA.122.059713

TBX20 Improves Contractility and Mitochondrial Function During Direct Human Cardiac Reprogramming

Perovskite-based photodetectors have great potential in light-signal conversion; the suppression of the dark current is regarded as one of the main concerns within the academic research communities to achieve a high-performance photodetector. Interfacial engineering in the transport layer is considered as one of the most essential methods for enhancement of perovskite photodetectors. Here, a nanocomposite thin film of tetra-sulfonated copper phthalocyanines and reduced graphene oxide (TS-CuPc/rGO) was investigated as the interfacial layer in perovskite-based photodetectors. Photodetectors with the TS-CuPc/rGO thin film as the interfacial layer exhibited a low dark current density of 2.2 × 10−8 A cm−2 at bias of −0.1 V as well as high responsivity and detectivity of ∼357 mA W−1 and ∼4.2 × 1012 jones, respectively; moreover, we observed an ON/OFF ratio of 7.33 × 103 to 520 nm light with an intensity of ∼0.077 mW cm−2. Our study revealed that with rGO additives, TS-CuPc molecules were favorable for the formation of an edge-on stacking film with high crystallinity. The rGO-induced crystalline TS-CuPc thin film with lower crystallographic defects effectively reduced the carrier recombination rate at the interfaces, leading to a suppressed dark current and enhanced photocurrent in the photodetector device, when compared to the less crystalline TS-CuPc layer.

/pdf/reduced-graphene-oxide-induced-crystallization-of-cupc-4kx40329iw.pdf

Reduced graphene oxide-induced crystallization of CuPc interfacial layer for high performance of perovskite photodetectors

Non-fullerene all-small-molecule organic solar cells (ASM-OSCs) have attracted considerable attention for industrial application owing to their well-defined molecular structure, high purity and good batch-to-batch reproducibility. However, nearly all the high power conversion efficiencies (PCEs) of ASM-OSCs rely heavily on the extra treatment of their active layers. Herein, two A-π-D-π-A-type benzodithiophene trimer (3BDT)-based large planar conjugated rigid small molecules (3BDT-4 and 3BDT-5) were successfully designed and synthesized. When blended with a non-fullerene acceptor (Y6), the 3BDT-4 and 3BDT-5-based solution-processed bulk heterojunction OSCs exhibited PCEs of 5.8% and 10.4% under 1.5G illumination without extra treatment, respectively. To the best of our knowledge, 3BDT-5 is the first small molecule-based OSC device with Y6 as an acceptor to exhibit a PCE breaking 10% without thermal annealing, solvent vapor annealing, or use of additives. More importantly, when using post-treatments on the 3BDT-5:Y6 blend film, the PCEs of the devices did not change obviously. Thus, the excellent photovoltaic properties of 3BDT-5 make it an alternative material for the industrial large-scale fabrication of high-performance OSCs. This result demonstrates that the molecular design method can be a very effective strategy for controlling the active layer morphology.

Jianqi Zhang

Papers

Study of photovoltaic performances for asymmetrical and symmetrical chlorinated thiophene-bridge-based conjugated polymers

Achieving 18.14% Efficiency of Ternary Organic Solar Cells with Alloyed Nonfullerene Acceptor

TBX20 Improves Contractility and Mitochondrial Function During Direct Human Cardiac Reprogramming

Reduced graphene oxide-induced crystallization of CuPc interfacial layer for high performance of perovskite photodetectors

Achieving 10% efficiency in non-fullerene all-small-molecule organic solar cells without extra treatments