Highly-efficient low-cost polarization-sensitive organic photodetectors based on laminated self-assembly planar and bulk heterojunctions.

To overcome the severe problems arising from the insufficient light absorption of ultrathin self-assembly active layers and the high cost use of ALD-grown low-leakage-current transport layers, we successfully developed a low-cost, simple and facile strategy of floating-film transfer and multilayer lamination (FFTML) for constructing highly-efficient ALD-free broadband polarization-sensitive organic photodetectors (OPDs) with the two commonly used structures of donor/acceptor planar heterojunction (PHJ) and donor:acceptor multilayer bulk heterojunction (BHJ). It was found that the PHJ-based polarization-sensitive OPD by FFTML possesses a low dark current due to the high carrier injection barrier, indicating it is more suitable to be applied in low polarized light detection scenarios. In contrast, the BHJ-based device by FFTML has a higher spectral responsivity in the whole wavelength due to more photo-excitons transferred to the donor:acceptor interface and dissociated into photoexcited carrirers. Furthermore, the film thickness, which is tuned by increasing lamination number of BHJ layers, has a big effect on the polarization-sensitive photodetection performance. The polarization-sensitive 4-BHJ OPD by FFTML finally achieved a high specific detectivity of 8.33 × 1010 Jones, which was much higher than 2.72 × 1010 Jones for the 2-BHJ device at 0 V. This work demonstrates that layer-by-layer lamination of self-assembly films can effectively improve the polarized-light detection performance, contributing significantly to the rapid development of the field.

A self-aligned assembling terahertz metasurface microfluidic sensor for liquid detection.

This paper reports a new terahertz metasurface microfluidic sensor, which is actually a kind of reflective terahertz metasurface absorber with a microfluidic-channel structure located in the strong field energy region of the absorber. The metasurface structure is made on an ultra-thin quartz substrate as the cap layer, while a two-step structure is made on a silicon substrate as the pedestal layer. In order to precisely control the thickness of the microfluidic channel, the cap layer is self-aligned assembled with the pedestal layer to form the terahertz metasurface microfluidic sensor. The obtained sensor could enhance the light-matter interaction, resulting in high sensing performance. The measured results show that the sensor has a perfect absorption peak at 2.60 THz and a high Q-factor of 62.59, which are basically consistent with the simulated results. The sensitivity and FOM calculated based on the measured results of different liquids with different refractive indices is 0.733 THz per RIU and 16.4, respectively. Compared with some recently related work, the sensitivity is increased by about 40%, the Q-factor is increased by 3-5 times, and the FOM is increased by 5 times, which make the sensor have great application potential for solution detection in the terahertz frequency band.

Sensitive Organic Photodetectors With Spectral Response up to 1.3 µm Using a Quinoidal Molecular Semiconductor.

Detecting short-wavelength infrared (SWIR) light has underpinned several emerging technologies. However, the development of highly sensitive organic photodetectors (OPDs) operating in the SWIR region is hindered by their poor external quantum efficiencies (EQEs) and high dark currents. Herein, the development of high-sensitivity SWIR-OPDs with an efficient photoelectric response extending up to 1.3 µm is reported. These OPDs utilize a new ultralow-bandgap molecular semiconductor featuring a quinoidal tricyclic electron-deficient central unit and multiple non-covalent conformation locks. The SWIR-OPD achieves an unprecedented EQE of 26% under zero bias and an even more impressive EQE of up to 41% under a -4 V bias at 1.10 µm, effectively pushing the detection limit of silicon photodetectors. Additionally, the low energetic disorder and trap density in the active layer lead to significant suppression of thermal-generation carriers and dark current, resulting in excellent detectivity (Dsh *) exceeding 1013 Jones from 0.50 to 1.21 µm and surpassing 1012 Jones even at 1.30 µm under zero bias, marking the highest achievements for OPDs beyond the silicon limit to date. Validation with photoplethysmography measurements, a spectrometer prototype in the 0.35-1.25 µm range, and image capture under 1.20 µm irradiation demonstrate the extensive applications of this SWIR-OPD.

All-Polymer Solar Cells and Photodetectors with Improved Stability Enabled by Terpolymers Containing Antioxidant Side Chains.

It is of vital importance to improve the long-term and photostability of organic photovoltaics, including organic solar cells (OSCs) and organic photodetectors (OPDs), for their ultimate industrialization. Herein, two series of terpolymers featuring with an antioxidant butylated hydroxytoluene (BHT)-terminated side chain, PTzBI-EHp-BTBHTx and N2200-BTBHTx (x = 0.05, 0.1, 0.2), are designed and synthesized. It was found that incorporating appropriate ratio of benzothiadiazole (BT) with BHT side chains on the conjugated backbone would induce negligible effect on the molecular weight, absorption spectra and energy levels of polymers, however, which would obviously enhance the photostability of these polymers. Consequently, all-polymer solar cells (all-PSCs) and photodetectors were fabricated, and the all-PSC based on PTzBI-EHp-BTBHT0.05: N2200 realized an optimal power conversion efficiency (PCE) approaching ~ 10%, outperforming the device based on pristine PTzBI-EHp: N2200. Impressively, the all-PSCs based on BHT-featuring terpolymers displayed alleviated PCEs degradation under continuous irradiation for 300 h due to the improved morphological and photostability of active layers. The OPDs based on BHT-featuring terpolymers achieved a lower dark current at - 0.1 bias, which could be stabilized even after irradiation over 400 h. This study provides a feasible approach to develop terpolymers with antioxidant efficacy for improving the lifetime of OSCs and OPDs.

Organic Photodiodes with Thermally Reliable Dark Current and Excellent Detectivity Enabled by Low Donor Concentration.

Reducing the dark current (Jd) under reverse bias while maintaining a high external quantum efficiency (EQE) is essential for the practical application of organic photodiodes (OPDs). However, the high Jd of OPDs is generally difficult to reduce because its origin in organic photodiodes is still not well understood and is strongly temperature dependent. To address the issues related to high Jd in typical OPDs, we investigate fullerene-based OPDs with various donor concentrations. It is surprising that OPDs with a low donor concentration in the active layer can achieve a very low Jd of 1.68 × 10-7 mA cm-2 at a reverse bias of -2 V, which is almost temperature-independent owing to the low polymer content. More importantly, the fullerene-based OPDs with a low donor concentration of 5 wt % can still achieve an external quantum efficiency (EQE) as high as 40%, resulting in a promisingly high detectivity of above 1013 Jones at 300-800 nm compared to the OPDs with a standard donor/acceptor ratio. The presented optimized OPD device can also be used for real-time heart rate detection, indicating its potential for practical photon-sensing applications.

Research on a high-sensitivity asymmetric metamaterial structure and its application as microwave sensor.

In this paper, an Asymmetric Electric Split-Ring Resonator (AESRR) metamaterial structure is proposed to explore the interaction between metamaterials and electromagnetic waves with the influence of Fano resonance on electromagnetic properties. With the symmetry of basic electric Split-Ring Resonator (eSRR) being broken, a new Fano resonant peak appears at around 11.575 GHz and this peak is very sensitive to the dielectric environment. Based on the proposed high sensitivity of AESRR, a microwave sensor based on a 13 × 13 arrays of AESRR was designed and verified using printed circuit board (PCB) technology. T-shape channel was integrated to the sensor by grooving in the FR-4 substrate which improved the integration and provided the feasibility of liquids detection. Seven organic liquids and four dielectric substrates are measured by this sensor. The measured results show the transmission frequency shifts from 11.575 to 11.150 GHz as the liquid samples permittivity changes from 1 to 7 and the transmission frequency shifts from 11.575 to 8.260 GHz as the solid substrates permittivity changes from 1 to 9. The results have proven the improved sensitivity and the larger frequency shift ∆f on material under test (MUTs) compared with the conventional reported sensor. The relative permittivity of liquid samples and solid samples can be obtained by establishing approximate models in CST, respectively. Two transcendental equations derived from measured results are proposed to predict the relative permittivity of liquid samples and solids samples. The accuracy and reliability of measured results and predicted results are numerically verified by comparing them with literature values. Thus, the proposed sensor has many advantages, such as low-cost, high-sensitivity, high-robustness, and extensive detecting range, which provided a great potential to be implemented in a lab-on-a-chip sensor system in the future.

Integration of chemical and biological methods: A case study of polycyclic aromatic hydrocarbons pollution monitoring in Shandong Peninsula, China.

Polycyclic aromatic hydrocarbons (PAHs), as persistent toxic substances (PTS), have been widely monitored in coastal environment, including seawater and sediment. However, scientific monitoring methods, like ecological risk assessment and integrated biomarker response, still need massive researches to verify their availabilities. This study was performed in March, May, August and October of 2018 at eight sites, Yellow River estuary (S1), Guangli Port (S2), Xiaying (S3), Laizhou (S4), Inner Bay (S5), Outer Bay (S6), Hongdao (S7) and Hongshiya (S8) of Shandong Peninsula, China. The contents of 16 priority PAHs in local seawater and sediment were determined, by which ecological risk assessment risk quotient (RQ) for seawater and sediment quality guidelines (SQGs) were calculated to characterize the PAHs pollution. Meanwhile, multiple biomarkers in the digestive gland of clam Ruditapes philippinarum were measured to represent different biological endpoints, including ethoxyresorufin-O-deethylase (EROD), glutathione S-transferase (GST), sulfotransferase (SULT), superoxide dismutase (SOD) and lipid peroxidation (LPO), by which integrated biomarker response (IBR) was calculated to provide a comprehensive assessment of environmental quality. Taken together, these results revealed the heaviest pollution at S2 as both PAHs concentrations and biomarkers responses reflected, and supported the integrated biomarker response as a useful tool for marine environmental monitoring, through its integration with SQGs.

Effects of Nrf2-Keap1 signaling pathway on antioxidant defense system and oxidative damage in the clams Ruditapes philippinarum exposure to PAHs.

NF-E2-related factor 2 (Nrf2) is a master regulator of antioxidant defense system which can maintain the oxidation balance in the cell. In our previous study, we first cloned the Nrf2 gene in clams and preliminarily explored the role of the Nrf2 at the transcription level. In this study, RNA interference (RNAi) technology was used to interfere with the expression of Nrf2 after being exposed to benzo(a)pyrene (BaP) for 5 days to verify the role of Nrf2 in the antioxidant defense system. Besides, we examined the mRNA expression and enzyme activities of antioxidases and the oxidative damage. The positive correlations between the Nrf2 with the mRNA expression and the enzyme activities of antioxidases indicated that Nrf2 was required for the induction of these antioxidant genes. Additionally, the mRNA expression and the enzyme activities of the glutathione peroxidase (GPx) in the Nrf2-dsRNA group were significantly higher than those in the control groups on the fifth day, indicating that the GPx is more sensitive to oxidative stress. Moreover, the oxidative damage in the RpNrf2-dsRNA group was markedly increased than control groups, indicating that Nrf2 transcriptional regulation may play an essential role in defending against oxidative damage. This study provides a foundation for further research on the mechanism of detoxification and antioxidation of polycyclic aromatic hydrocarbons (PAHs) in the clams at the transcription level and the protein level.

Biomonitoring of polycyclic aromatic hydrocarbons (PAHs) from Manila clam Ruditapes philippinarum in Laizhou, Rushan and Jiaozhou, bays of China, and investigation of its relationship with human carcinogenic risk.

This study examined the marine environment and seafood safety using chemical monitoring and multiple biomarkers. Samples were collected from three bays on the Shandong Peninsula in China, Laizhou, Rushan and Jiaozhou, in March, May, August, and October of 2018 and 2019. The polycyclic aromatic hydrocarbon (PAH) concentrations in sediments and tissue samples from the clam Ruditapes philippinarum and multiple biomarkers were measured. All the sampling sites were found to be medium-PAH-contaminated areas (100-1000 ng/g d.w.). According to the correlation analysis, ethoxyresorufin-o-deethylase (EROD) and superoxide dismutase (SOD) activity in the clam's digestive gland were sensitive to PAHs (p < .05), but the incremental lifetime cancer risk (ILCR) was lower than the priority risk level (10-4) at most sampling sites. EROD, SOD and acetylcholinesterase activity exhibited significant correlations with the ILCR values (p < .01), suggesting that they may serve as good indicators for assessing safe seafood consumption levels for human beings.

A verification of correlation between chemical monitoring and multi-biomarker approach using clam Ruditapes philippinarum and scallop Chlamys farreri to assess the impact of pollution in Shandong coastal area of China.

Biogeochemical monitoring coupled with multi-biomarker approach were performed for the assessment of marine environment, using clam Ruditapes philippinarum and scallop Chlamys farreri to indicate contamination status in sediments and seawater respectively. The bivalves were collected from three stations, Jiaozhou Bay, Rushan Bay and Laizhou Bay, of Shandong coastal area. A series of contaminants (PAHs and TBBPA) and biomarkers (AhR, EROD, GST, SOD, GPx, CAT, DNA damage) were measured. Multi-biomarker pollution index (MPI) and integrated biomarker response (IBR) were carried out to evaluate contamination status and both indexes showed that Rushan Bay was most polluted, where the pollution level of sediments reached "highly polluted" in August, followed by Jiaozhou Bay and Rushan Bay which reached "lightly polluted". The correlation of IBR values with contaminants' concentrations was verified through the Pearson correlation coefficient (p < 0.05), consolidating this scientific assessment method for marine environment.

The molecular mechanism of AhR-ARNT-XREs signaling pathway in the detoxification response induced by polycyclic aromatic hydrocarbons (PAHs) in clam Ruditapes philippinarum.

The aryl hydrocarbon receptor (AhR) has been known primarily for its role in the regulation of several drug and xenobiotic metabolizing enzymes to mitigate environmental stresses. In this study, we interfere the expression of AhR gene to investigate the mechanism of AhR signaling pathway in the detoxification and antioxidation defense system that induced by Polycyclic Aromatic Hydrocarbons (PAHs) exposure by RNA interference (RNAi). The gene expressions of aryl hydrocarbon receptor nuclear translocator (ARNT), heat shock protein 90 (Hsp90) were evaluated after being exposed to benzo(a)pyrene (BaP) (4 µg/L) for 5 days and the positive correlations between AhR, ARNT, HSP90 indirectly indicating that AhR may have the ability to bind to ligands such as PAHs in Ruditapes philippinarum (R. philippinarum). Besides, the activities of detoxification enzymes were determined to investigate the role of AhR signaling pathway played in the metabolic detoxification. What's more, the gene expressions of protein kinase C (PKC) signaling pathway, mitogen-activated protein kinase (MAPKs) signaling pathway, NF-E2-related factor 2 (Nrf2) signaling pathway and antioxidant defense system indicated that AhR may regulate the Nrf2-Keap1 signaling pathway through Kelch-like ECH-associated protein-1 (Keap1) and MAPKs, PKC signaling pathways. In conclusion, adoption of RNA interference technology to explore the role of RpAhR gene played in the detoxification and antioxidation defense system under the PAHs stress at different time points can informe molecular endpoints for application towards ecotoxicology monitoring of bivalves.

Enhanced photoresponse in curled graphene ribbons.

Graphene has become one of the most promising materials for future optoelectronics due to its ultrahigh charge-carrier mobility, high light transmission, and universal absorbance in the near-infrared and visible spectral ranges. However, a zero band gap and ultrafast recombination of the photoexcited electron-hole pairs limit graphene's potential in photovoltaic generation. Recent studies have shown that hot carriers can enhance photovoltaic generation in graphene p-n junctions through the photothermoelectric effect (PTE). It is, therefore, desirable to synthesize graphene nanostructures with an intrinsic PTE-induced photocurrent response. Here we report a simple method to synthesize quasi-one dimensional (quasi-1D) curled graphene ribbons (CGRs) that generate a photocurrent response with two orders of magnitude enhancement. Scanning photocurrent and photoluminescence measurements reveal that the photocurrent response is primarily attributed to the PTE and that the infrared emission may arise from thermal radiation. These results offer a new way to fabricate graphene-based optoelectronics with an enhanced photoresponse.

Controlling the growth morphology of carbon nanotubes: from suspended bridges to upright forests.

We have developed two strategies to produce carbon nanotubes (CNTs) from low-density surface growth to high-density forest growth. We have demonstrated that by introducing a C(2)H(2) pulse at the beginning of the growth, where methane is still used as the main carbon feeding gas, the growth tendency of CNTs can be changed and the resulting growth morphology will vary from surface growth to forest growth. Similarly, the growth morphology can be changed when the growth temperature is raised. The further characterization via Raman spectroscopy indicates that an increasing C(2)H(2) pulse time will lead to a rise of the D peak for as-grown CNTs, due to the formation of more multi-walled CNTs and the amorphous carbon contamination introduced by extra C(2)H(2), while a high growth temperature tends to produce high-quality CNTs and to reduce the amorphous carbon contamination. Furthermore, by appropriately adjusting the growth temperature and controlling the C(2)H(2) pulse time, we have managed to produce both suspended CNT bridges and upright forests within a single growth procedure and to form suspended pristine CNT transistors with a relatively high yield. In addition, the electrical properties of these CNT nanostructures have been investigated by electrical transport and scanning photocurrent measurements.