School of Chemistry - Research Publications

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Author: Hall, Christopher × Author: Smith, Trevor × End date: 2019 × Start date: 2019 ×

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    Resolving the Mechanisms of Photocurrent Improvement in Ternary Organic Solar Cells
    Bi, PQ ; Hall, CR ; Yin, H ; So, SK ; Smith, TA ; Ghiggino, KP ; Hao, XT (AMER CHEMICAL SOC, 2019-08-01)
    The ultralow band gap small-molecule IEICO-4F has been employed as a secondary acceptor in both fullerene-based (PTB7-Th:PC71BM) and nonfullerene-based (PBDB-T:ITIC) ternary organic solar cells (OSCs). Structural characterization methods combined with ultrafast spectroscopy have been applied to resolve the mechanisms, leading to the observed improvement in device efficiency upon addition of IEICO-4F. It is shown that IEICO-4F forms ternary mixed domains in the host systems and improves the device efficiency by broadening the absorption spectral range and enhancing both charge separation and charge transport. The enhanced crystallinity of the semiconductor polymer electron donors in the presence of the EIECO-4 provides additional channels for ultrafast charge transfer and transport compared to binary systems. The optimum ternary blend formulations required to improve device efficiencies are reported. This work provides new insights into the fabrication of high-performance ternary OSCs.
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    Tetraphenylethene 9,10-Diphenylanthracene Derivatives - Synthesis and Photophysical Properties
    Gao, C ; Seow, JY ; Zhang, B ; Hall, CR ; Tilley, AJ ; White, JM ; Smith, TA ; Wong, WWH (WILEY-V C H VERLAG GMBH, 2019-06)
    A series of tetraphenylethene 9,10-diphenylanthracene (TPE-DPA) derivatives have been synthesized, and their photophysical properties studied. Photoluminescence measurements in PMMA, neat films and nanoparticle dispersions reveal that different aggregation states are formed, which leads to different photophysical behavior. The triplet excited state properties were studied using Pt(II) octaethylporphyrin (PtOEP) as triplet sensitizer. Upconverted emission from the DPA moiety is observed in nanoparticle dispersions of each derivative. A higher upconverted emission intensity is observed in aerated (compared to deaerated) solutions of the derivatives following irradiation, which is attributed to oxidation of the TPE moiety. These results provide valuable insight for the design of AIE luminogens for triplet-triplet annihilation upconversion (TTA-UC).
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    Visualizing Phase Segregation in Mixed-Halide Perovskite Single Crystals
    Mao, W ; Hall, CR ; Chesman, ASR ; Forsyth, C ; Cheng, Y-B ; Duffy, NW ; Smith, TA ; Bach, U (WILEY-V C H VERLAG GMBH, 2019-02-25)
    Mixed organolead halide perovskites (MOHPs), CH3 NH3 Pb(Brx I1-x )3 , have been shown to undergo phase segregation into iodide-rich domains under illumination, which presents a major challenge to their development for photovoltaic and light-emitting devices. Recent work suggested that phase-segregated domains are localized at crystal boundaries, driving investigations into the role of edge structure and the growth of larger crystals with reduced surface area. Herein, a method for growing large (30×30×1 μm3 ) monocrystalline MAPb(Brx I1-x )3 single crystals is presented. The direct visualization of the growth of nanocluster-like I-rich domains throughout the entire crystal revealed that grain boundaries are not required for this transformation. Narrowband fluorescence imaging and time-resolved spectroscopy provided new insight into the nature of the phase-segregated domains and the collective impact on the optoelectronic properties.
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    Visualisierung der Phasensegregation in Gemischthalogenid‐ Perowskiteinkristallen
    Mao, W ; Hall, CR ; Chesman, ASR ; Forsyth, C ; Cheng, Y ; Duffy, NW ; Smith, TA ; Bach, U (Wiley, 2019-02-25)
    Abstract Es hat sich gezeigt, dass Organoblei‐Gemischthalogenid‐Perowskite (MOHPs), CH3NH3Pb(BrxI1−x)3, unter Belichtung eine Phasensegregation zu I‐reichen Domänen eingehen, was eine Herausforderung für ihre Nutzung in Photovoltaik‐ und lichtemittierenden Elementen darstellt. Auf Basis neuster Resultate wird vermutet, dass die Phasensegregation entlang der Kristallkanten lokalisiert ist, weshalb sich die Forschung auf die Rolle von Grenzstrukturen und das Züchten größerer Kristalle mit geringerer Oberfläche konzentrierte. Hier wird eine Methode zur Züchtung großer (30×30×1 μm3) monokristalliner MA(BrxI1−x)3‐Einkristalle präsentiert. Durch direkte Visualisierung des Wachstums nanoclusterartiger I‐reicher Domänen über den gesamten Kristall hinweg konnte gezeigt werden, dass für diese Transformation Korngrenzen nicht essenziell sind. Bildgebende Verfahren auf Basis schmalbandiger Fluoreszenz sowie zeitaufgelöste Spektroskopie gaben neue Einblicke in die Phasensegregationsdomänen sowie deren Auswirkungen auf optoelektronische Eigenschaften dieser Materialien.