| 1. |
- Zhang, Xuning, et al.
(author)
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On the understanding of energy loss and device fill factor trade-offs in non-fullerene organic solar cells with varied energy levels
- 2020
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In: Nano Energy. - : ELSEVIER. - 2211-2855 .- 2211-3282. ; 75
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Journal article (peer-reviewed)abstract
- Fill factor (FF) is an important parameter governing the power conversion efficiency (PCE) in non-fullerene organic solar cells (NF-OSCs), which however is less studied than the other two parameters (short-circuit current J(sc) and open-circuit voltage V-oc). To understand how energy offsets, exciton and charge carrier dynamics impact the FF, four groups of bulk heterojunctions (BHJs) NF-OSCs are investigated with FFs varying from 0.61 to 0.78 under progressive changes of HOMO-HOMO offsets (Delta(HOMOs), from 0.09 to 0.24 eV). By pump-probe optical spectroscopy, we find that the FF exhibits a positive dependence on Delta(HOMO) and charge-separated state lifetime (tau(CS)) in the blends, a result of inhibited back charge transfers and recombination at the donor-acceptor interface under higher Delta(HOMO)s. Moreover, we observe a fast charge extraction with decreased sensitivity to internal electric-fields in high-FF devices. Despite these merits, the gains of FF are at the expense of increasing the voltage loss to non-radiative recombination in our studied systems. The combined results suggest that remaining appropriate energetic offsets is essential for controlling the carrier dynamics with longer-lived CS-states, restraining charge back transfer and reducing charge recombination toward high FFs and photovoltaic efficiencies.
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| 2. |
- Bai, Yang, et al.
(author)
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Geometry design of tethered small-molecule acceptor enables highly stable and efficient polymer solar cells
- 2023
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In: Nature Communications. - : NATURE PORTFOLIO. - 2041-1723. ; 14:1
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Journal article (peer-reviewed)abstract
- With the power conversion efficiency of binary polymer solar cells dramatically improved, the thermal stability of the small-molecule acceptors raised the main concerns on the device operating stability. Here, to address this issue, thiophene-dicarboxylate spacer tethered small-molecule acceptors are designed, and their molecular geometries are further regulated via the thiophene-core isomerism engineering, affording dimeric TDY-alpha with a 2, 5-substitution and TDY-beta with 3, 4-substitution on the core. It shows that TDY-alpha processes a higher glass transition temperature, better crystallinity relative to its individual small-molecule acceptor segment and isomeric counterpart of TDY-beta, and amore stablemorphology with the polymer donor. As a result, the TDY-alpha based device delivers a higher device efficiency of 18.1%, and most important, achieves an extrapolated lifetime of about 35000 hours that retaining 80% of their initial efficiency. Our result suggests that with proper geometry design, the tethered small-molecule acceptors can achieve both high device efficiency and operating stability.
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| 3. |
- Deng, Min, et al.
(author)
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Genome-wide association analyses in Han Chinese identify two new susceptibility loci for amyotrophic lateral sclerosis
- 2013
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In: Nature Genetics. - : Nature Publishing Group. - 1061-4036 .- 1546-1718. ; 45:6, s. 697-
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Journal article (peer-reviewed)abstract
- To identify susceptibility genes for amyotrophic lateral sclerosis (ALS), we conducted a genome-wide association study (GWAS) in 506 individuals with sporadic ALS and 1,859 controls of Han Chinese ancestry. Ninety top SNPs suggested by the current GWAS and 6 SNPs identified by previous GWAS were analyzed in an independent cohort of 706 individuals with ALS and 1,777 controls of Han Chinese ancestry. We discovered two new susceptibility loci for ALS at 1q32 (CAMK1G, rs6703183, P-combined = 2.92 x 10(-8), odds ratio (OR) = 1.31) and 22p11 (CABIN1 and SUSD2, rs8141797, P-combined = 2.35 x 10(-9), OR = 1.52). These two loci explain 12.48% of the overall variance in disease risk in the Han Chinese population. We found no association evidence for the previously reported loci in the Han Chinese population, suggesting genetic heterogeneity of disease susceptibility for ALS between ancestry groups. Our study identifies two new susceptibility loci and suggests new pathogenic mechanisms of ALS.
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| 4. |
- Li, Shangyu, et al.
(author)
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Tethered Small-Molecule Acceptors Simultaneously Enhance the Efficiency and Stability of Polymer Solar Cells
- 2023
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In: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 35
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Journal article (peer-reviewed)abstract
- For polymer solar cells (PSCs), the mixture of polymer donors and small-molecule acceptors (SMAs) is fine-tuned to realize a favorable kinetically trapped morphology and thus a commercially viable device efficiency. However, the thermodynamic relaxation of the mixed domains within the blend raises concerns related to the long-term operational stability of the devices, especially in the record-holding Y-series SMAs. Here, a new class of dimeric Y6-based SMAs tethered with differential flexible spacers is reported to regulate their aggregation and relaxation behavior. In their polymer blends with PM6, it is found that they favor an improved structural order relative to that of Y6 counterpart. Most importantly, the tethered SMAs show large glass transition temperatures to suppress the thermodynamic relaxation in mixed domains. For the high-performing dimeric blend, an unprecedented open circuit voltage of 0.87 V is realized with a conversion efficiency of 17.85%, while those of regular Y6-base devices only reach 0.84 V and 16.93%, respectively. Most importantly, the dimer-based device possesses substantially reduced burn-in efficiency loss, retaining more than 80% of the initial efficiency after operating at the maximum power point under continuous illumination for 700 h. The tethering approach provides a new direction to develop PSCs with high efficiency and excellent operating stability.
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| 5. |
- Wang, Jianqiu, et al.
(author)
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A Comparative Study on Hole Transfer Inversely Correlated with Driving Force in Two Non-Fullerene Organic Solar Cells
- 2019
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In: The Journal of Physical Chemistry Letters. - : AMER CHEMICAL SOC. - 1948-7185. ; 10:14, s. 4110-4116
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Journal article (peer-reviewed)abstract
- We report a faster rate of hole transfer under a smaller AHomo in a comparative study of two group organic solar cells (OSCs) consisting of IT-4F as an acceptor and PBDBT and PBDBT-SF as donors. In the OSCs based on PBDBT. SF:IT-4F, a higher short-circuit current (J(SC)) was observed with a Delta(Homo) of 0.31 eV compared to a lower Jsc in PBDBT:IT-4F OSCs with a larger Delta(Homo) (0.45 eV). Intensive investigation indicates that the rate of transfer of a hole from IT-4F to PBDBT-SF or PBDBT is inversely proportional to the Delta(Homo) between IT-4F and donors. The larger Jsc in the PBDBT-SF:IT-4F device is attributed to a synergy of faster hole transfer, slower recombination, and rapid charge extraction enabled by desired morphology and balanced charge carrier mobilities with PBDBT-SF, suggesting that under a sufficiently high Delta(Homo), comprehensive considerations of the transport, film morphology, and energy levels are needed when designing new materials for high-performance OSCs.
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| 6. |
- Fan, Qunping, 1989, et al.
(author)
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Over 14% efficiency all-polymer solar cells enabled by a low bandgap polymer acceptor with low energy loss and efficient charge separation
- 2020
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In: Energy & Environmental Science. - : Royal Society of Chemistry. - 1754-5692 .- 1754-5706. ; 13:12, s. 5017-5027
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Journal article (peer-reviewed)abstract
- Obtaining both high open-circuit voltage (V-oc) and short-circuit current density (J(sc)) has been a major challenge for efficient all-polymer solar cells (all-PSCs). Herein, we developed a polymer acceptor PF5-Y5 with excellent optical absorption capability (onset extending to similar to 880 nm and maximum absorption coefficient exceeding 105 cm(-1) in a film), high electron mobility (3.18 x 10(3) cm(2) V-1 s(-1)) and high LUMO level (-3.84 eV) to address such a challenge. As a result, the PBDB-T:PF5-Y5-based all-PSCs achieved a high power conversion efficiency of up to 14.45% with both a high Voc (0.946 V) and a high Jsc (20.65 mA cm(-2)), due to the high and broad absorption coverage, small energy loss (0.57 eV) and efficient charge separation and transport in the device, which are among the best values in the all-PSC field. In addition, the all-PSC shows a similar to 15% improvement in PCE compared to its counterpart small molecule acceptor (Y5)-based device. Our results suggest that PF5-Y5 is a very promising polymer acceptor candidate for applications in efficient all-PSCs.
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| 7. |
- Jiang, Kui, et al.
(author)
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Suppressed recombination loss in organic photovoltaics adopting a planar-mixed heterojunction architecture
- 2022
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In: Nature Energy. - : NATURE PORTFOLIO. - 2058-7546. ; 7:11, s. 1076-1086
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Journal article (peer-reviewed)abstract
- At present, high-performance organic photovoltaics mostly adopt a bulk-heterojunction architecture, in which exciton dissociation is facilitated by charge-transfer states formed at numerous donor-acceptor (D-A) heterojunctions. However, the spin character of charge-transfer states originated from recombination of photocarriers allows relaxation to the lowest-energy triplet exciton (T-1) at these heterojunctions, causing photocurrent loss. Here we find that this loss pathway can be alleviated in sequentially processed planar-mixed heterojunction (PMHJ) devices, employing donor and acceptor with intrinsically weaker exciton binding strengths. The reduced D-A intermixing in PMHJ alleviates non-geminate recombination at D-A contacts, limiting the chance of relaxation, thus suppressing T-1 formation without sacrificing exciton dissociation efficiency. This resulted in devices with high power conversion efficiencies of >19%. We elucidate the working mechanisms for PMHJs and discuss the implications for material design, device engineering and photophysics, thus providing a comprehensive grounding for future organic photovoltaics to reach their full promise. Organic solar cells with a bulk-heterojunction architecture suffer from photocurrent loss driven by triplet states. Now, Jiang et al. show that sequentially deposited donor-acceptor planar-mixed heterojunctions suppress triplet formation, enabling efficiencies over 19%.
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| 8. |
- Shi, Furong, et al.
(author)
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A Nitroxide Radical Conjugated Polymer as an Additive to Reduce Nonradiative Energy Loss in Organic Solar Cells
- 2023
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 35:23
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Journal article (peer-reviewed)abstract
- Nonfullerene-acceptor-based organic solar cells (NFA-OSCs) are now set off to the 20% power conversion efficiency milestone. To achieve this, minimizing all loss channels, including nonradiative photovoltage losses, seems a necessity. Nonradiative recombination, to a great extent, is known to be an inherent material property due to vibrationally induced decay of charge-transfer (CT) states or their back electron transfer to the triplet excitons. Herein, it is shown that the use of a new conjugated nitroxide radical polymer with 2,2,6,6-tetramethyl piperidine-1-oxyl side groups (GDTA) as an additive results in an improvement of the photovoltaic performance of NFA-OSCs based on different active layer materials. Upon the addition of GDTA, the open-circuit voltage (VOC), fill factor (FF), and short-circuit current density (JSC) improve simultaneously. This approach is applied to several material systems including state-of-the-art donor/acceptor pairs showing improvement from 15.8% to 17.6% (in the case of PM6:Y6) and from 17.5% to 18.3% (for PM6:BTP-eC9). Then, the possible reasons behind the observed improvements are discussed. The results point toward the suppression of the CT state to triplet excitons loss channel. This work presents a facile, promising, and generic approach to further improve the performance of NFA-OSCs.
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| 9. |
- Xu, Qiang, et al.
(author)
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Theoretical prediction, synthesis, and crystal structure determination of new MAX phase compound V2SnC
- 2020
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In: JOURNAL OF ADVANCED CERAMICS. - : SPRINGER. - 2226-4108 .- 2227-8508. ; 9:4, s. 481-492
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Journal article (peer-reviewed)abstract
- Guided by the theoretical prediction, a new MAX phase V2SnC was synthesized experimentally for the first time by reaction of V, Sn, and C mixtures at 1000 degrees C. The chemical composition and crystal structure of this new compound were identified by the cross-check combination of first-principles calculations, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and high resolution scanning transmission electron microscopy (HR-STEM). The stacking sequence of V2C and Sn layers results in a crystal structure of space group P6(3)/mmc. Thea- andc-lattice parameters, which were determined by the Rietveld analysis of powder XRD pattern, are 0.2981(0) nm and 1.3470(6) nm, respectively. The atomic positions are V at 4f (1/3, 2/3, 0.0776(5)), Sn at 2d (2/3, 1/3, 1/4), and C at 2a (0, 0, 0). A new set of XRD data of V2SnC was also obtained. Theoretical calculations suggest that this new compound is stable with negative formation energy and formation enthalpy, satisfied Born-Huang criteria of mechanical stability, and positive phonon branches over the Brillouin zone. It also has low shear deformation resistancec(44)(second-order elastic constant,c(ij)) and shear modulus (G), positive Cauchy pressure, and low Pughs ratio (G/B= 0.500 < 0.571), which is regarded as a quasi-ductile MAX phase. The mechanism underpinning the quasi-ductility is associated with the presence of a metallic bond.
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| 10. |
- Yan, Zhibo, et al.
(author)
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Reversible Ionic Polarization in Metal Halide Perovskites
- 2021
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In: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 125:1, s. 283-289
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Journal article (peer-reviewed)abstract
- Metal halide perovskites have emerged as promising photovoltaic materials with attractive photoelectronic properties. However, the fundamental mechanisms for their outstanding properties are still elusive. In this work, we reveal the reversible bulk ionic polarization property of perovskites through studying the photoelectric response on the controllable states by electrical poling from room temperature to low temperature (200 K). The overall increase in light absorption, photoconductance, and carrier recombination lifetime demonstrates that the bulk ionic polarization contributes to the excellent photoelectric properties of halide perovskites. Moreover, we also discuss the role of ionic polarization in the overshoot transient photocurrent relaxation phenomenon after the electrical poling. This work would promote deep understanding in the unique properties of perovskites and their excellent photovoltaic performance.
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