Optimization of Ultrasonic-assisted Extraction and Fatty Acid Composition of Oil from Paeonia suffruticosa Andr. Seed.

Response surface methodology (RSM) was applied to optimize the effects of extraction parameters including time, power, temperature and liquid-to-solid ratio on peony seed oil yield. Box-Behnken design (BBD) was employed for optimization of extraction parameters in oil yield that extracted assisting by ultrasonic while petroleum ether as solvent. The chemical composition of peony seed oil under optimal condition in ultrasonic-assisted extract method was analyzed by gas chromatography-mass spectrometry (GC-MS). The optimal conditions were that extraction time 45 min, extraction temperature 45°C, extraction power 90 W and liquid-to-solid ratio 7:1, respectively. Under this condition, the extraction yield value was 33.90% which was with 95% confidence level, hence indicated the reliability of RSM in optimizing ultrasonic-assisted extraction of oil from Paeonia suffruticosa Andr. seed. Three unsaturated fatty acid of peony oil such as n-3 α-linolenic acid (39.75%), n-6 linoleic acid (26.32%) and the oleic acid (23.66%), totally more than 89.00% was determined at optimum condition.

Efficient Energy Funneling in Quasi-2D Perovskites: From Light Emission to Lasing.

Quasi-2D Ruddlesden-Popper halide perovskites with a large exciton binding energy, self-assembled quantum wells, and high quantum yield draw attention for optoelectronic device applications. Thin films of these quasi-2D perovskites consist of a mixture of domains having different dimensionality, allowing energy funneling from lower-dimensional nanosheets (high-bandgap domains) to 3D nanocrystals (low-bandgap domains). High-quality quasi-2D perovskite (PEA)2 (FA)3 Pb4 Br13 films are fabricated by solution engineering. Grazing-incidence wide-angle X-ray scattering measurements are conducted to study the crystal orientation, and transient absorption spectroscopy measurements are conducted to study the charge-carrier dynamics. These data show that highly oriented 2D crystal films have a faster energy transfer from the high-bandgap domains to the low-bandgap domains (<0.5 ps) compared to the randomly oriented films. High-performance light-emitting diodes can be realized with these highly oriented 2D films. Finally, amplified spontaneous emission with a low threshold 4.16 µJ cm-2 is achieved and distributed feedback lasers are also demonstrated. These results show that it is important to control the morphology of the quasi-2D films to achieve efficient energy transfer, which is a critical requirement for light-emitting devices.

Long-Wavelength Lead Sulfide Quantum Dots Sensing up to 2600 nm for Short-Wavelength Infrared Photodetectors.

Lead sulfide nanoparticles (PbS NPs) are used in the short-wavelength infrared photodetectors because of their excellent photosensitivity, band gap tunability, and solution processability. It has been a challenge to synthesize high-quality PbS NPs with an absorption peak beyond 2000 nm. In this work, using PbS seed crystals with an absorption peak at 1960 nm, we report a successful synthesis of very large monodispersed PbS NPs having a diameter up to 16 nm by multiple injections. The resulting NPs have an absorption peak over 2500 nm with a small full width at half-maximum of 24 meV. To demonstrate the applications of such large quantum dots (QDs), broadband heterojunction photodetectors are fabricated with the large PbS QDs of an absorption peak at 2100 nm. The resulting devices have an external quantum efficiency (EQE) of 25% (over 50% internal quantum efficiency) at 2100 nm corresponding to a responsivity of 0.385 A/W and an EQE of ∼60% in the visible range.

Randomly Distributed Conjugated Polymer Repeat Units for High-Efficiency Photovoltaic Materials with Enhanced Solubility and Processability.

Three structurally disordered terpolymer derivatives of PffBT4T-2OD (PCE11), prepared by replacing a varied amount of bithiophene linkers with single thiophenes, were found to exhibit reduced aggregation in solution with increasing thiophene content, while important redox and optoelectronic properties remained similar to those of PffBT4T-2OD. Solar cells based on random terpolymer-PC71BM blends exhibited average power conversion efficiencies of over 9.5% when processed with preheated substrates, with fill factors above 70%, exceeding those from PffBT4T-2OD. Thanks to increased solubility, random terpolymer devices were able to be fabricated on room-temperature substrates, reaching virtually identical performance among all three polymers despite remarkable thicknesses of ∼400 nm. Thus, we show that the random terpolymer approach is successful in improving processability while maintaining device performance.

Increased Exciton Delocalization of Polymer upon Blending with Fullerene.

Interfaces between donor and acceptor in a polymer solar cell play a crucial role in exciton dissociation and charge photogeneration. While the importance of charge transfer (CT) excitons for free carrier generation is intensively studied, the effect of blending on the nature of the polymer excitons in relation to the blend nanomorphology remains largely unexplored. In this work, electroabsorption (EA) spectroscopy is used to study the excited-state polarizability of polymer excitons in several polymer:fullerene blend systems, and it is found that excited-state polarizability of polymer excitons in the blends is a strong function of blend nanomorphology. The increase in excited-state polarizability with decreased domain size indicates that intermixing of states at the interface between the donor polymers and fullerene increases the exciton delocalization, resulting in an increase in exciton dissociation efficiency. This conclusion is further supported by transient absorption spectroscopy and time-resolved photoluminescence measurements, along with the results from time-dependent density functional theory calculations. These findings indicate that polymer excited-state polarizability is a key parameter for efficient free carrier generation and should be considered in the design and development of high-performance polymer solar cells.

Langmuir-Blodgett Thin Films of Diketopyrrolopyrrole-Based Amphiphiles.

We report on two π-conjugated donor-acceptor-donor (D-A-D) molecules of amphiphilic nature, aiming to promote intermolecular ordering and carrier mobility in organic electronic devices. Diketopyrrolopyrrole was selected as the acceptor moiety that was disubstituted with nonpolar and polar functional groups, thereby providing the amphiphilic structures. This structural design resulted in materials with a strong intermolecular order in the solid state, which was confirmed by differential scanning calorimetry and polarized optical microscopy. Langmuir-Blodgett (LB) films of ordered mono- and multilayers were transferred onto glass and silicon substrates, with layer quality, coverage, and intermolecular order controlled by layer compression pressure on the LB trough. Organic field-effect transistors and organic photovoltaics devices with active layers consisting of the amphiphilic conjugated D-A-D-type molecules were constructed to demonstrate that the LB technique is an effective layer-by-layer deposition approach to fabricate self-assembled, ordered thin films.