School of Chemistry - Research Publications

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    Suppressing Kinetic Aggregation of Non-Fullerene Acceptor via Versatile Alloy States Enables High-Efficiency and Stable Ternary Polymer Solar Cells
    Zhang, K-N ; Guo, J-J ; Zhang, L-J ; Qin, C-C ; Yin, H ; Gao, X-Y ; Hao, X-T (Wiley, 2021-05-17)
    Despite considerable advances devoted to improving the operational stability of organic solar cells (OSCs), the metastable morphology degradation remains a challenging obstacle for their practical application. Herein, the stabilizing function of the alloy states in the photoactive layer from the perspective of controlling the aggregation characteristics of non‐fullerene acceptors (NFAs), is revealed. The alloy‐like model is adopted separately into host donor and acceptor materials of the state‐of‐the‐art binary PM6:BTP‐4Cl blend with the self‐stable polymer acceptor PDI‐2T and small molecule donor DRCN5T as the third components, delivering the simultaneously enhanced photovoltaic efficiency and storage stability. In such ternary systems, two separate arguments can rationalize their operating principles: (1) the acceptor alloys strengthen the conformational rigidity of BTP‐4Cl molecules to restrain the intramolecular vibrations for rapid relaxation of high‐energy excited states to stabilize BTP‐4Cl acceptor. (2) The donor alloys optimize the fibril network microstructure of PM6 polymer to restrict the kinetic diffusion and aggregation of BTP‐4Cl molecules. According to the superior morphological stability, non‐radiative defect trapping coefficients can be drastically reduced without forming the long‐lived, trapped charge species in ternary blends. The results highlight the novel protective mechanisms of engineering the alloy‐like composites for reinforcing the long‐term stability of NFA‐based ternary OSCs.
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    Ternary-Assisted Sequential Solution Deposition Enables Efficient All-Polymer Solar Cells with Tailored Vertical-Phase Distribution
    Cui, F-Z ; Chen, Z-H ; Qiao, J-W ; Wang, T ; Lu, G-H ; Yin, H ; Hao, X-T (Wiley, 2022-06-10)
    All-polymer solar cells (all-PSCs) have received attention in recent years for their desirable properties in power conversion efficiency and long-term operational stability. However, it is still a big challenge to acquire an “ideal” vertical-phase distribution of polymer/polymer blends due to the non-ideal molecular conformations and mixing behaviors. Herein, a ternary-assisted sequential solution deposition (SSD) strategy is adopted to regulate the vertical compositional profile of all-PSCs. A favorable acceptor(donor)-enriched phase near the cathode(anode) can be obtained by a ternary-assisted SSD strategy. With such a compositional profile, the exciton yield and carrier density can be enhanced by the vertical component gradient. Remarkably, the non-geminate recombination is suppressed with an improved exciton diffusion length (15.36 nm) that delivers an outstanding power conversion efficiency over 16% of the ternary PM6/PY-IT:PDI-2T SSD devices. This work demonstrates the success of ternary-assisted SSD strategy in reorganizing the vertical-phase distribution, which provides a feasible route for a potential ternary device construction toward efficient all-polymer photovoltaics.
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    Reducing Limitations of Aggregation-Induced Photocarrier Trapping for Photovoltaic Stability via Tailoring Intermolecular Electron-Phonon Coupling in Highly Efficient Quaternary Polymer Solar Cells
    Zhang, K-N ; Du, X-Y ; Chen, Z-H ; Wang, T ; Yang, Z-Q ; Yin, H ; Yang, Y ; Qin, W ; Hao, X-T (Wiley, 2022-02-10)
    The kinetic aggregation of nonfullerene acceptors under nonequilibrium conditions can induce electron–phonon interaction roll-off and electronic band structure transition, which represents an important limitation for long-term operational stability of organic solar cells (OSCs). However, the fundamental underlying mechanisms have received limited attention. Herein, a photophysical correlation picture between intermolecular electron–phonon coupling and trapping of electronic excitation is proposed based on the different aggregation behaviors of BTP-eC9 in bulk-heterojunction and layer-by-layer processed multicomponent OSCs. Two separate factors rationalize their correlation mechanisms: 1) the local lattice and/or molecular deformation can be regarded as the results of BTP-eC9 aggregates in binary system under continuous heating, which brings about attenuated intermolecular electron–phonon coupling with intensified photocarrier trapping. 2) The higher density of trap states with more extended tails into the bandgap give rise to the formation of highly localized trapped polarons with a longer lifetime. The stabilized intermolecular electron–phonon coupling through synergistic regulation of donor and acceptor materials effectively suppresses unfavorable photocarrier trapping, delivering the improved device efficiency of 18.10% and enhanced thermal stability in quaternary OSCs. These results provide valuable property–function insights for further boosting photovoltaic stability in view of modulating intermolecular electron–phonon coupling.
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    Reducing Limitations of Aggregation‐Induced Photocarrier Trapping for Photovoltaic Stability via Tailoring Intermolecular Electron–Phonon Coupling in Highly Efficient Quaternary Polymer Solar Cells (Adv. Energy Mater. 6/2022)
    Zhang, K ; Du, X ; Chen, Z ; Wang, T ; Yang, Z ; Yin, H ; Yang, Y ; Qin, W ; Hao, X (Wiley, 2022-02)
    In article number 2103371, Xiao-Yan Du, Xiao-Tao Hao and co-workers rationalize the underlying correlation mechanisms between intermolecular electron-phonon coupling and trapping of electronic excitation behind the kinetic aggregation behaviors of BTP-eC9 in bulk-heterojunction and layer-by-layer processed multicomponent organic solar cells.
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    Extracellular vesicular lipids as biomarkers for the diagnosis of Alzheimer’s disease
    Su, H ; Rustam, YH ; Masters, CL ; Makalic, E ; McLean, C ; Hill, AF ; Barnham, KJ ; Reid, GE ; Vella, LJ (Wiley, 2021-12-31)
    An increasing number of studies have revealed that dysregulated lipid homeostasis is associated with the pathological processes that lead to Alzheimer’s disease (AD). If changes in key lipid species could be detected in the periphery, it would advance our understanding of the disease and facilitate biomarker discovery. Global lipidomic profiling of sera/blood however has proved challenging with limited disease or tissue specificity. Small extracellular vesicles (EV) in the central nervous system, can pass the blood-brain barrier and enter the periphery, carrying a subset of lipids that could reflect lipid homeostasis in brain. This makes EVs uniquely suited for peripheral biomarker exploration.
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    Global double hybrids do not work for charge transfer: A comment on "Double hybrids and time-dependent density functional theory: An implementation and benchmark on charge transfer excited states"
    Casanova-Paez, M ; Goerigk, L (Wiley, 2021-03-30)
    We comment on the results published by Ottochian et al. in J. Comput Chem. 2020, 41, 1242. Therein, the authors claim that the second-order, perturbative correlation correction applied to the time-dependent version of the PBE-QIDH global double-hybrid functional approximation (DHDFA) enables the description of charge-transfer (CT) excitations. Herein, we point out some inadvertent oversights related to what had already been previously known and achieved in the field of time-dependent DHDFAs. Exemplified for the same four systems that Ottochian et al. have used to analyze intermolecular CT excitations, we show how a systematic and unacceptably large redshift in global DHDFAs is rectified when using the latest long-range corrected DHDFAs published earlier in J. Chem. Theory Comput. 2019, 15, 4735.
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    Phase Transition Modulation and Defect Suppression in Perovskite Solar Cells Enabled by a Self-Sacrificed Template
    Xiong, Z ; Chen, S ; Zhao, P ; Cho, Y ; Odunmbaku, GO ; Zheng, Y ; Jones, DJ ; Yang, C ; Sun, K (WILEY-V C H VERLAG GMBH, 2021-09)
    Tunable crystal growth offering highly aligned perovskite crystallites with suppressed deep‐level defects is vital for efficient charge transport, which in turn significantly influences the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Herein, a “precursor to perovskite‐like template to perovskite” (PPP) growth strategy is developed, using either MAAc or GuaCl precursor to induce a sacrificial thermal–unstable perovskite‐like template for (FAPbI3)x(MAPbI3)y perovskite growth. The self‐sacrificed intermediate template induces the formation of highly aligned perovskite crystals with greatly enhanced film crystallinity and suppresses deep‐level defect formation. Furthermore, it is proved that MAAc or GuaCl completely evaporates during the high‐temperature annealing process. The reduction in defect densities and nonradiative recombination enhances both carrier lifetime and charge dynamics, yielding impressive PCEs of 22.3% and 22.8% with a high open‐circuit voltage (VOC) of 1.16 V and an incredible fill factor (FF) of 81.5% and 79.4% for MAAc‐ and GuaCl‐based devices, respectively. These results suggest that the formation of the thermal–unstable perovskite‐like sacrificial template is a promising strategy to restrain the deep‐level defects in perovskite films toward the attainment of highly efficient and stable large‐scale PSCs as well as other perovskite‐based electronics.
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    Photophysics and spectroscopy of 1,2-Benzazulene
    Awuku, S ; Bradley, SJ ; Ghiggino, KP ; Steer, RP ; Stevens, AL ; White, JM ; Yeow, C (Elsevier, 2021-12)
    The electronic spectroscopy and photophysics of 1,2-benzazulene (BzAz) have been examined in solution and in thin solid films, with the objective of comparing its intramolecular and intermolecular excited state decay processes with those of azulene. Unlike azulene, the S2 – S0 absorption and fluorescence spectra exhibit a clear mirror image relationship dominated by a single strong Franck-Condon active progression. Picosecond transient absorption spectra and non-linear S2 fluorescence upconversion experiments reveal lifetimes that follow a well-established energy gap law correlation, indicative of a dominant S2 – S1 decay route. Mechanistic interpretations, including the possibility of S2 singlet fission in aggregates, are discussed.
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    A sandwich-like structural model revealed for quasi-2D perovskite films
    Zheng, F ; Hall, CR ; Angmo, D ; Zuo, C ; Rubanov, S ; Wen, Z ; Bradley, SJ ; Hao, X-T ; Gao, M ; Smith, TA ; Ghiggino, KP (Royal Society of Chemistry, 2021-04-28)
    The excellent performance and stability of perovskite solar cells (PSCs) based on quasi-2D Ruddlesden–Popper perovskites (RPPs) holds promise for their commercialization. Further improvement in the performance of 2D PSCs requires a detailed understanding of the microstructure of the quasi-2D perovskite films. Based on scanning transmission electron microscopy (STEM), time-resolved photoluminescence, and transient absorption measurements, a new sandwich-like structural model is proposed to describe the phase distribution of RPPs. In contrast to the conventional gradient distribution, it is found that small-n RPPs are sandwiched between large-n RPP phase layers at the front and back sides owing to crystallization initiated from both interfaces during film formation. This sandwich-like distribution profile facilitates excitons funneling from the film interior to both surfaces for dissociation while free carriers transport via large-n channels that permeate the film to ensure efficient charge collection by the corresponding electrodes, which is favorable for high-performance photovoltaics. This discovery provides a new fundamental understanding of the operating principles of 2D PSCs and has valuable implications for the design and optimization strategies of optoelectronic devices based on quasi-2D RPPs films.
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    A luminescent solar concentrator ray tracing simulator with a graphical user interface: features and applications
    Zhang, B ; Yang, H ; Warner, T ; Mulvaney, P ; Rosengarten, G ; Wong, WWH ; Ghiggino, KP (IOP PUBLISHING LTD, 2020-07)
    A Monte-Carlo ray tracing simulator with a graphical user interface (MCRTS-GUI) has been developed to provide a quantitative description, performance evaluation and photon loss analysis of luminescent solar concentrators (LSCs). The algorithm is applied to several practical LSC device structures including multiple dyes in the same waveguiding layer, and structures where a dye layer is sandwiched between clear substrates. The effect of the host matrix absorption and the influence of the neighboring layers are investigated. Validations demonstrate that the MCRTS-GUI developed provides a reliable and accurate description of LSC performance. Code for the mixed-dye single layer configuration is converted into a ray-tracing package with a user-friendly interface and is made available as open source software.