Effective control of mode transition is one of the key technologies for dual-mode scramjet. In this study, a 3-dimensional unsteady Reynolds-averaged Navier-Stokes modeling was used to investigate the effects of equivalence ratio, inflow temperature, and pilot hydrogen on transient process of mode transition in a dual-mode scramjet combustor. The isolator entrance Mach number was 2.5, and the fuel of vaporized kerosene was used in the combustor with pilot hydrogen. The results showed that during mode transition from ram mode to scram mode induced by reducing the equivalence ratio of kerosene, the disappearance of the high-pressure zone around the kerosene injector was the sign of approaching the achievement of mode transition. The leading edge of the shock train moved downstream and the strength of shock train was significantly weakened. During this process, the distribution of heat release zone transformed from scattered along the combustor to being concentrated in the cavity. Then, the opposite process was studied when the inflow temperature was reduced from 1750 to 1000 K while the equivalence ratio was kept the same. The thickness of shear layers originated from the fuel injectors significantly increased. Altering the amount of pilot hydrogen can significantly influence the flow field in the combustor. It showed that the increase of pilot hydrogen could shield the kerosene vapor entering into the high-temperature zone in the cavity and hindered the formation of concentrated heat release. Thus, the overall heat release became more dispersed.
It is demonstrated that the side-chain engineering of polymer donors and molecular conformation of small-molecule acceptors (SMAs) plays a crucial role in the morphology and photovoltaic performance of polymer solar cells (PSCs). However, the synergetic effect of these two aspects has been rarely reported. Herein, two wide-band gap donor–acceptor (D–A) copolymers (PST-TTC and PSPT-TTC) featuring the same main-chain backbone but different conjugated side chains were developed and combined with three low-band gap symmetric SMAs (ITIC, DTCFO-ICCl, and Y6) with various molecular conformations (S-shape, C-shape, and U-shape) to investigate the synergetic effect of side-chain engineering of polymer donors and conformation manipulation of SMAs on molecular properties, device physics, film morphology, and photovoltaic performance. The results indicate that PST-TTC with an alkylthiothiophene side chain exhibits a broader absorption spectrum, a smaller optical band gap (1.95 vs 1.99 eV), and a deeper-lying highest occupied molecular orbital (HOMO) level (−5.39 vs −5.36 eV) as compared to PSPT-TTC with an alkylthiophenylthiophene side chain. The PSCs were constructed according to the different donor/acceptor combinations based on the two as-synthesized polymers and three selected SMAs. After optimization, PST-TTC paired with S-shaped ITIC provides a power conversion efficiency (PCE) of 10.10% and the PCE can be further improved up to 10.60% when C-shaped DTCFO-ICCl was used to replace ITIC as the acceptor. However, the device performance becomes worse, accompanied with a sharply reduced PCE of 7.36% after the substitution of ITIC for U-shaped Y6. On the contrary, when the paired donor was changed to PSPT-TTC, the PSPT-TTC:Y6-based PSC achieves a remarkably increased PCE of up to 11.46%. These delicate observations suggest that the polymer donor with different conjugated side chains should collaborate with symmetric SMAs possessing various molecular conformations to realize superior morphology and device performance.
All polymer solar cells (all-PSCs) is one of the important emerging renewable energy technologies. In this work, we use "jacketing" effect liquid crystalline polymer (LCP) with perylenediimide as side chain to fabricate all-PSCs. First, poly(2,5-bis{[6-(4-alkoxy-4′-perylenediimide)-6-hexyl]oxycarbonyl}styrene) (abbreviated as PPDCS) is successfully synthesized via chain polymerization. The resultant polymer PPDCS forms stable smectic C (SmC) structure until decomposition. The electrochemical experiment indicates PPDCS shows deep LUMO energy level of −3.81 eV, thus, the nonconjugated PPDCS can be employed as acceptor materials to build all-PSCs. Atomic force microscopy (AFM) experiments show that the PBT7/PPDCS blend film forms a bicontinuous network-domains and the resultant film shows extensive absorption spectrum (300–800 nm) on UV–vis spectra. All-PSCs device fabricated by PTB7/PPDCS presents the best power conversion efficiency (PCE) of 1.23% after optimization, where the short-circuit current density (Jsc) is 4.34 mA cm–2, an open-circuit voltage (Voc) is 0.65 V, and a fill factor (FF) is 0.37. This work suggests that the nonconjugated LCP shows potential application for solar cell.
Four arylmethylene-substituted small-molecule acceptors (SMAs), IDTV-SiIC, IDTVT-PhIC, m-IDTV-PhIC, and DTCFDV-IC were introduced to the host PBDB-T:PC71BM binary system as a guest acceptor to construct PBDB-T:PC71BM:SMA ternary polymer solar cells (PSCs), respectively. After optimization, these ternary PSCs exhibit power conversion efficiencies (PCEs) of 8.93%, 9.28%, 9.68%, and 9.78% for IDTV-SiIC, IDTVT-PhIC, m-IDTV-PhIC, and DTCFDV-IC, respectively, all of which are higher than those of the host binary PSC regardless of the device structures (inverted or conventional devices). The improved PCE is first attributed to the increased open-circuit voltage (Voc) due to the upshifted lowest unoccupied molecular orbital level of an acceptor alloy between the host acceptor (PC71BM) and the guest acceptors (SMAs). The acceptor alloy model is verified by exploring the relationship between Voc and the feed ratio of SMA in the acceptor blend, cyclic voltammetry measurements, and miscibility of two kinds of acceptors. Furthermore, the increased fill factors of ternary PSCs also play a key role in improving the PCEs, which could be ascribed to the enhanced and more balanced carrier mobilities, increased exciton dissociation, reduced charge recombination, and the optimized morphology of active layers after such SMAs were added as the guest acceptor. In particular, IDTV-SiIC-based thick-film ternary devices were prepared, and the results demonstrate that the ternary device has a better film thickness tolerance compared with the host binary device, suggesting a great potential of such SMAs in fabricating thick-film photovolatic devices. Additionally, relative to the host PM6:L8-BO binary PSC (17.18%), a higher PCE of 18.20% was achieved in the PM6:L8-BO:DTCFDV-IC ternary PSC, with DTCFDV-IC as the guest acceptor, implying such arylmethylene-substituted SMAs have certain great potentiality in constructing high-efficiency ternary PSCs. This work suggests that the incorporation of these SMAs as the third component to construct ternary PSCs is a feasible and effective strategy to obviously enhance the device efficiency.
Subtle modification of the electron-withdrawing end group (A) of small-molecule acceptors (SMAs) plays an important role in regulating structure, optoelectronic properties, and device performance. To obtain SMAs for nonhalogenated solvent-processing devices, we develop two A–D–A SMAs (IT-ClBr and IT-FBr) based on indacenodithieno[3,2-b]thiophene (D) by employing hybrid dihalogenated 1,1-dicyanomethylene-3-indanone (IC-ClBr and IC-FBr) as A groups. The effects of hybrid dihalogenated end groups on the solubility, photoelectrochemical properties, morphology, and device performance were investigated by comprehensively comparing with similar SMAs (IT-4F and IT-4Cl) using nonhybrid dihalogenated IC as A groups. Absorption spectra of IT-ClBr and IT-FBr are similar to that of IT-4Cl but red-shifted relative to that of IT-4F. Hybrid dihalogenation results in enhancing absorption ability and elevating the lowest unoccupied molecular orbitals (LUMOs) of the corresponding SMAs, which is beneficial to increasing short-circuit current density (Jsc) and open-circuit voltage (Voc), respectively. Furthermore, the solubility of IT-ClBr and IT-FBr in nonhalogenated solvents o-xylene (o-XY) can be improved, which makes it possible to fabricate devices with environmentally friendly nonhalogenated solvents. Using polymer PM6 as donor material, IT-FBr-based polymer solar cells (PSCs) present a higher power conversion efficiency (PCE) of 12.02% compared to IT-ClBr (PCE = 10.79%) with o-XY as the solvent and 0.5 vol % 1,8-diiodoactane (DIO) as the additive, owing to the increased Voc and fill factor (FF), which is also comparable to that of IT-4Cl (PCE = 12.14%). More importantly, the PCE can be further improved up to 12.35% when 1 vol % 2-methylnaphthalene (2-MN) replaced DIO as the additive, which is obviously superior to that of IT-4F (PCE = 10.11%). The enhanced efficiency could be attributed to the improved solubility in the nonhalogenated solvent and optimal miscibility between SMAs and the polymer donor (PM6). This finding suggests that hybrid dihalogenation on end groups is a feasible strategy to tailor the solubility, crystallinity, and miscibility of SMAs, thereby improving the morphology and device performance of PSCs fabricated with eco-friendly solvents and additives.
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