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  1. Abstract

    Photoelectrode materials are the heart of photoelectrochemical (PEC) cells, which hold great promise to address global energy and environmental issues by converting solar energy into electricity or chemical fuels. In recent decades, significant research efforts have been devoted to the design and construction of photoelectrodes for the efficient generation and utilization of charge carriers to boost PEC performance. Herein, insights from a literature study on the relationship between the architecture and charge dynamics of photoelectrodes are presented. After briefly introducing the fundamental theories of charge dynamics in nanostructured photoelectrodes, the development of photoelectrode design in 1D polycrystalline nanotube arrays, 1D single‐crystalline nanowire arrays, and hierarchical and mesoporous nanowire arrays is reviewed with a focus on the interplay between architecture and charge transport properties. For each design, commonly used synthetic approaches and the corresponding charge transport properties are discussed. Subsequently, the applications of these photoelectrodes in PEC systems are summarized. In conclusion, future challenges in the rational design of photoelectrode architecture are presented. The basic relationships between the architectures and charge dynamics of photoelectrode materials discussed here are expected to provide pertinent guidance and a reference for future advanced material design targeting improved light energy conversion systems.

     
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  2. Abstract

    Hybrid organic–inorganic perovskites such as methylammonium lead iodide have emerged as promising semiconductors for energy‐relevant applications. The interactions between charge carriers and lattice vibrations, giving rise to polarons, have been invoked to explain some of their extraordinary optoelectronic properties. Here, time‐resolved optical spectroscopy is performed, with off‐resonant pumping and electronic probing, to examine several representative lead iodide perovskites. The temporal oscillations of electronic bandgaps induced by coherent lattice vibrations are reported, which is attributed to antiphase octahedral rotations that dominate in the examined 3D and 2D hybrid perovskites. The off‐resonant pumping scheme permits a simplified observation of changes in the bandgap owing to theAgvibrational mode, which is qualitatively different from vibrational modes of other symmetries and without increased complexity of photogenerated electronic charges. The work demonstrates a strong correlation between the lead–iodide octahedral framework and electronic transitions, and provides further insights into the manipulation of coherent optical phonons and related properties in hybrid perovskites on ultrafast timescales.

     
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  3. Abstract

    The chemical stabilities of hybrid perovskite materials demand further improvement toward long‐term and large‐scale photovoltaic applications. Herein, the enhanced chemical stability of CH3NH3PbI3is reported by doping the divalent anion Se2−in the form of PbSe in precursor solutions to enhance the hydrogen‐bonding‐like interactions between the organic cations and the inorganic framework. As a result, in 100% humidity at 40 °C, the 10% w/w PbSe‐doped CH3NH3PbI3films exhibited >140‐fold stability improvement over pristine CH3NH3PbI3films. As the PbSe‐doped CH3NH3PbI3films maintained the perovskite structure, a top efficiency of 10.4% with 70% retention after 700 h aging in ambient air is achieved with an unencapsulated 10% w/w PbSe:MAPbI3‐based cell. As a bonus, the incorporated Se2−also effectively suppresses iodine diffusion, leading to enhanced chemical stability of the silver electrodes.

     
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  4. Kafafi, Zakya (Ed.)
    Abstract In hybrid perovskite solar cells (PSCs), the reaction of hydrogens (H) located in the amino group of the organic A-site cations with their neighboring halides plays a central role in degradation. Inspired by the retarded biological activities of cells in heavy water, we replaced the light H atom with its abundant, twice-as-heavy, nonradioactive isotope, deuterium (D) to hamper the motion of H. This D substitution retarded the formation kinetics of the detrimental H halides in Pb-based PSCs, as well as the H bond-mediated oxidation of Sn2+ in Sn–Pb-based narrow-bandgap PSCs, evidenced by accelerated stability studies. A computational study indicated that the zero point energy of D-based formamidinium (FA) is lower than that of pristine FA. In addition, the smaller increase in entropy in D-based FA than in pristine FA accounts for the increased formation free energy of the Sn2+ vacancies, which leads to the retarded oxidation kinetics of Sn2+. In this study, we show that substituting active H with D in organic cations is an effective way to enhance the stability of PSCs without sacrificing photovoltaic (PV) performance. This approach is also adaptable to other stabilizing methods. 
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  5. null (Ed.)
  6. High-performance optoelectronic devices, such as solar cells and light-emitting diodes, have been fabricated with lead halide perovskites owing to their superior carrier properties. However, charge transport in such optoelectronics is intrinsically directional due to the existence of p–n junctions, which thus lacks the potential to elucidate any perturbations in light or electricity during energy conversion. Here, with the presence of a LiCl additive in a formamidinium chloride (FACl) solution, the as-grown LiCl:FAPbCl 3 nanorods demonstrate greatly enhanced crystallinity and UV photoresponse as compared to pristine FAPbCl 3 nanostructures without the LiCl additive. Most importantly, the LiCl:FAPbCl 3 nanorod film exhibits unprecedented distinguishability to UV photons with different energies and oscillating intensities, in the form of bipolar and periodically oscillatory photocurrents. This work could advance the fundamental understanding of photoinduced carrier processes in halide perovskites and facilitate the development of novel UV-based optical communications. 
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