Browsing by Author "Nie, Wanyi"

Now showing 1 - 3 of 3
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    Design principles for electronic charge transport in solution-processed vertically stacked 2D perovskite quantum wells
    (Springer Nature, 2018) Tsai, Hsinhan; Asadpour, Reza; Blancon, Jean-Christophe; Stoumpos, Constantinos C.; Even, Jacky; Ajayan, Pulickel M.; Kanatzidis, Mercouri G.; Alam, Muhammad Ashraful; Mohite, Aditya D.; Nie, Wanyi
    State-of-the-art quantum-well-based devices such as photovoltaics, photodetectors, and light-emission devices are enabled by understanding the nature and the exact mechanism of electronic charge transport. Ruddlesden-Popper phase halide perovskites are two-dimensional solution-processed quantum wells and have recently emerged as highly efficient semiconductors for solar cell approaching 14% in power conversion efficiency. However, further improvements will require an understanding of the charge transport mechanisms, which are currently unknown and further complicated by the presence of strongly bound excitons. Here, we unambiguously determine that dominant photocurrent collection is through electric field-assisted electron-hole pair separation and transport across the potential barriers. This is revealed by in-depth device characterization, coupled with comprehensive device modeling, which can self-consistently reproduce our experimental findings. These findings establish the fundamental guidelines for the molecular and device design for layered 2D perovskite-based photovoltaics and optoelectronic devices, and are relevant for other similar quantum-confined systems.
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    Highly efficient photoelectric effect in halide perovskites for regenerative electron sources
    (Springer Nature, 2021) Liu, Fangze; Sidhik, Siraj; Hoffbauer, Mark A.; Lewis, Sina; Neukirch, Amanda J.; Pavlenko, Vitaly; Tsai, Hsinhan; Nie, Wanyi; Even, Jacky; Tretiak, Sergei; Ajayan, Pulickel M.; Kanatzidis, Mercouri G.; Crochet, Jared J.; Moody, Nathan A.; Blancon, Jean-Christophe; Mohite, Aditya D.
    Electron sources are a critical component in a wide range of applications such as electron-beam accelerator facilities, photomultipliers, and image intensifiers for night vision. We report efficient, regenerative and low-cost electron sources based on solution-processed halide perovskites thin films when they are excited with light with energy equal to or above their bandgap. We measure a quantum efficiency up to 2.2% and a lifetime of more than 25 h. Importantly, even after degradation, the electron emission can be completely regenerated to its maximum efficiency by deposition of a monolayer of Cs. The electron emission from halide perovskites can be tuned over the visible and ultraviolet spectrum, and operates at vacuum levels with pressures at least two-orders higher than in state-of-the-art semiconductor electron sources.
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    Supramolecular block copolymer photovoltaics through ureido-pyrimidinone hydrogen bonding interactions
    (Royal Society of Chemistry, 2016) Lin, Yen-Hao; Nie, Wanyi; Tsai, Hsinhan; Li, Xiaoyi; Gupta, Gautam; Mohite, Aditya D.; Verduzco, Rafael
    A challenge in the development of bulk heterojunction organic photovoltaics (BHJ OPVs) is achieving a desirable nanoscale morphology. This is particularly true for polymer blend OPVs in which large-scale phase separation occurs during processing. Here, we present a versatile approach to control the morphology in polymer blend OPVs through incorporation of self-associating 4 2-ureido-4[1H]-pyrimidinone (UPy) endgroups onto donor and acceptor conjugated polymers. These UPy functionalized polymers associate to form supramolecular block copolymers during solution blending and film casting. Atomic force microscopy measurements show that supramolecular associations can improve film uniformity. We find that the performance of supramolecular block copolymer OPVs improves from 0.45% to 0.77% relative to the non-associating conjugated polymer blends at the same 155 °C annealing conditions. Impedance measurements reveal that UPy endgroups both increase the resistance for charge recombination and for bulk charge transport. This work represents a versatile approach to reducing large-scale phase separation in polymer–polymer blends and directing the morphology through supramolecular interactions.