Two-Dimensional Conjugated Polymer Based on sp2-Carbon Bridged Indacenodithiophene for Efficient Polymer Solar Cells

2D polyaniline derivatives as turn-on fluorescent probe for efficient triethylamine detection at room temperature

Due to the severe toxicity of triethylamine (TEA), the preparation of chemsensors with high sensitivity, low cost and visualization for TEA detection has been a research hotspot. However, based on the fluorescence turn-on detection of TEA remains rare. In this work, three two-dimensional conjugated polymers (2D CPs) were prepared by chemical oxidation polymerization. These sensors show a quick response and excellent selectivity toward TEA at room temperature. The minimum limit of detection (LOD) for TEA was 3.6 nM in the range of 10 μM ∼ 30 μM. Interestingly, the paper sensor based on P2-HCl can quantitatively detect TEA gas within 20 s, which showed great application potential in fields of environmental monitoring. Besides, Fourier transform infrared spectra (FT-IR), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) data were used to thoroughly interpret the sensing mechanism. This work provided an effective method for the development of 2D fluorescent chemosensors for TEA detection.

Nanomaterials as multimodal photothermal agents (PTAs) against 'Superbugs'

Superbugs, also known as multidrug-resistant bacteria, have become a lethal and persistent threat due to their unresponsiveness toward conventional antibiotics. The main reason for this is that superbugs can rapidly mutate and restrict any foreign drug/molecule in their vicinity. Herein, nanomaterial-mediated therapies have set their path and shown burgeoning efficiency toward the ablation of superbugs. Notably, treatment modalities like photothermal therapy (PTT) have shown prominence in killing multidrug-resistant bacteria with their ability to generate local heat shock-mediated hyperthermia in such species. However, photothermal treatment has some serious limitations, such as high cost, complexity, and even toxicity to some extent. Hence, it is important to resolve such shortcomings of PTTs as they provide substantial tissue penetration. This is why multimodal PTTs have emerged and taken over this domain of research for the past few years. In this work, we have summarized and critically reviewed such exceptional works of recent times and provided a perspective to enhance their efficiencies. Profoundly, we discuss the design rationales of some novel photothermal agents (PTAs) and shed light on their mechanisms. Finally, challenges for PTT-derived multimodal therapy are presented, and capable synergistic bactericidal prospects are anticipated.

Modulation of the Fluorination Site on Side-Chain Thiophene Improved Efficiency in All-Small-Molecule Organic Solar Cells

Fine-tuning the phase-separated morphology is of great importance to achieve efficient all-small-molecule organic solar cells (ASM-OSCs). In this work, a pair of isomers are designed and synthesized, namely, BDT-UF and BDT-DF, in which the fluorine atom in BDT-UF is close to the alkyl chain of side-chain thiophene, while that in BDT-DF is close to the center core. Owing to the noncovalent interaction between fluorine and hydrogen, BDT-DF shows a smaller dihedral angle between the thiophene side chain and the BDT core, which causes better molecular planarity. When mixed with N3, BDT-UF shows better miscibility, higher crystallinity, and more ordered molecule stacking in the blend film. Finally, the device of BDT-DF:N3 gains a power conversion efficiency (PCE) of 14.5%, while that of BDT-UF:N3 shows an increase in Voc, Jsc, and FF and gains a PCE of 15.1%. Our work exhibits a way of adjusting the substitution site of fluorine atoms to improve the PCE of ASM-OSCs.

Reduced Nonradiative Recombination Energy Loss Enabled Efficient Polymer Solar Cells via Tuning Alkyl Chain Positions on Pendent Benzene Units of Polymers

Nonradiative recombination energy loss (ΔE₃) plays a key role in enhancing device efficiencies for polymer solar cells (PSCs). Until now, there is no clear resolution for reducing ΔE₃ via molecular design. Herein, we report two conjugated polymers, PBDB-P-p and PBDB-P-m, which are integrated from benzo[1,2-b:4,5-b']dithiophene with alkylthio chain substituted at para- or meta-position on pendent benzene and benzo[1,2-c:4,5-c']dithiophene-4,8-dione. Both the polymers have different temperature-dependent aggregation properties but similar molecular energy levels. When BO-4Cl was used as an acceptor to fabricate PSCs, the device of PBDB-P-p:BO-4Cl displayed a maximal power conversion efficiency (PCE) of 13.83%, while the best device of PBDB-P-m:BO-4Cl exhibited a higher PCE of 14.12%. The close J_SCs and fill factors in both PSCs are attributed to their formation of effective nanoscale phase separation as confirmed by atomic force microscopy measurements. We find that the PBDB-P-m-based device has 1 order of magnitude higher electroluminescence quantum efficiency (EQE_EL) than in the PBDB-P-p-based one, which could arise from the relatively weak aggregation in the PBDB-P-m-based film. Thus, the PBDB-P-m-based device has a remarkably enhanced V_OC of 0.86 V in contrast to 0.80 V in the PBDB-P-p-based device. This study offers a feasible structural optimization way on the alkylthio side chain substitute position on the conjugated polymer to enhance V_OC by reducing nonradiative recombination energy loss in the resulting PSCs.

Fluorination Effect for Highly Conjugated Alternating Copolymers Involving Thienylenevinylene-Thiophene-Flanked Benzodithiophene and Benzothiadiazole Subunits in Photovoltaic Application

Two two-dimensional (2D) donor-acceptor (D-A) type conjugated polymers (CPs), namely, PBDT-TVT-BT and PBDT-TVT-FBT, in which two ((E)-(4,5-didecylthien-2-yl)vinyl)- 5-thien-2-yl (TVT) side chains were introduced into 4,8-position of benzo[1,2-b:4,5-b']dithiophene (BDT) to synthesize the highly conjugated electron-donating building block BDT-TVT, and benzothiadiazole (BT) and/or 5,6-difluoro-BT as electron-accepting unit, were designed to systematically ascertain the impact of fluorination on thermal stability, optoelectronic property, and photovoltaic performance. Both resultant copolymers exhibited the lower bandgap (1.60 ~ 1.69 eV) and deeper highest occupied molecular orbital energy level (EHOMO, -5.17 ~ -5.37 eV). It was found that the narrowed absorption, deepened EHOMO and weakened aggregation in solid film but had insignificant influence on thermal stability after fluorination in PBDT-TVT-FBT. Accordingly, a PBDT-TVT-FBT-based device yielded 16% increased power conversion efficiency (PCE) from 4.50% to 5.22%, benefited from synergistically elevated VOC, JSC, and FF, which was mainly originated from deepened EHOMO, increased μh, μe, and more balanced μh/μe ratio, higher exciton dissociation probability and improved microstructural morphology of the photoactive layer as a result of incorporating fluorine into the polymer backbone.

Increased conjugated backbone twisting to improve carbonylated-functionalized polymer photovoltaic performance

Two conjugated polymers containing different linkers were synthesized to study their photovoltaic performances.

Synthesis of Conjugated Polymers Containing B←N Bonds with Strong Electron Affinity and Extended Absorption

The B←N is isoelectronic to the C-C, with the former having stronger dipole moment and higher electron affinity. Replacing the C-C bonds in conjugated polymers with B←N bonds is an effective pathway toward novel polymers with strong electron affinity and adjustable optoelectronic properties. In this work, we synthesize a conjugated copolymer, namely, BNIDT-DPP, based on a B←N embedded unit, BNIDT, and a typical electron-deficient unit, diketopyrrolopyrrole (DPP). For comparison, the C-C counterpart, i.e., IDT-DPP, is also synthesized. In contrast to IDT-DPP, the B←N embedded polymer BNIDT-DPP shows an extended absorption edge (836 versus 978 nm), narrowed optical bandgap (1.48 versus 1.27 eV), and higher electron affinity (3.54 versus 3.74 eV). The Gaussian simulations reveal that the B←N embedded polymer BNIDT-DPP is more electron-deficient in contrast to IDT-DPP, supporting the decreased bandgap and energy levels of BNIDT-DPP. Organic thin-film transistor (OTFT) tests indicate a well-defined p-type characteristic for both IDT-DPP and BNIDT-DPP. The hole mobilities of IDT-DPP and BNIDT-DPP tested by OTFTs are 0.059 and 0.035 cm²/V·s, respectively. The preliminary fabrication of all-polymer solar cells based on BNIDT-DPP and PBDB-T affords a PCE of 0.12%. This work develops a novel B←N embedded polymer with strong electron affinity and extended absorption, which is potentially useful for electronic device application.

Impact of the Bonding Sites at the Inner or Outer π-Bridged Positions for Non-Fullerene Acceptors

Two A-π-D-π-A-type non-fullerene acceptors (IDT-T_oFIC and IDT-T_iFIC) with 5-hexylthienyl chains substituted at the inner and outer β-positions of the thiophene π-bridge have been designed, respectively. Impacts of varied positional modifications are systematically studied. By utilizing PBDB-T as the donor, polymer solar cells are constructed with these two molecules as acceptors. Power conversion efficiencies of 11.09 and 9.46% are acquired for IDT-T_oFIC- and IDT-T_iFIC-based devices, respectively. Our studies have demonstrated that the use of thiophene spacers carrying one conjugated side chain at different positions can markedly enhance the photovoltaic properties relative to the corresponding control molecule IDTT2F.

Effect of linear side-chain length on the photovoltaic performance of benzodithiophene-alt-dicarboxylic ester terthiophene polymers

Two conjugated polymers with different side chains were synthesized to study their photovoltaic performances.