Browsing by Author "Kanatzidis, Mercouri G."

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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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    High-phase purity two-dimensional perovskites with 17.3% efficiency enabled by interface engineering of hole transport layer
    (Elsevier, 2021) Sidhik, Siraj; Wang, Yafei; Li, Wenbin; Zhang, Hao; Zhong, Xinjue; Agrawal, Ayush; Hadar, Ido; Spanopoulos, Ioannis; Mishra, Anamika; Traoré, Boubacar; Samani, Mohammad H. K.; Katan, Claudine; Marciel, Amanda B.; Blancon, Jean-Christophe; Even, Jacky; Kahn, Antoine; Kanatzidis, Mercouri G.; Mohite, Aditya D.
    State-of-the-art p-i-n-based 3D perovskite solar cells (PSCs) use nickel oxide (NiOX) as an efficient hole transport layer (HTL), achieving efficiencies >22%. However, translating this to phase-pure 2D perovskites has been unsuccessful. Here, we report 2D phase-pure Ruddlesden-Popper BA2MA3Pb4I13 perovskites with 17.3% efficiency enabled by doping the NiOX with Li. Our results show that progressively increasing the doping concentration transforms the photoresistor behavior to a typical diode curve, with an increase in the average efficiency from 2.53% to 16.03% with a high open-circuit voltage of 1.22 V. Analysis reveals that Li doping of NiOX significantly improves the morphology, crystallinity, and orientation of 2D perovskite films and also affords a superior band alignment, facilitating efficient charge extraction. Finally, we demonstrate that 2D PSCs with Li-doped NiOX exhibit excellent photostability, with T99 = 400 h at 1 sun and T90 of 100 h at 5 suns measured at relative humidity of 60% ± 5% without the need for external thermal management.
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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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    Long periodic ripple in a 2D hybrid halide perovskite structure using branched organic spacers
    (Royal Society of Chemistry, 2020) Hoffman, Justin M.; Malliakas, Christos D.; Sidhik, Siraj; Hadar, Ido; McClain, Rebecca; Mohite, Aditya D.; Kanatzidis, Mercouri G.
    Two-dimensional (2D) halide perovskites have great promise in optoelectronic devices because of their stability and optical tunability, but the subtle effects on the inorganic layer when modifying the organic spacer remain unclear. Here, we introduce two homologous series of Ruddlesden–Popper (RP) structures using the branched isobutylammonium (IBA) and isoamylammonium (IAA) cations with the general formula (RA)2(MA)n−1PbnI3n+1 (RA = IBA, IAA; MA = methylammonium n = 1–4). Surprisingly, the IAA n = 2 member results in the first modulated 2D perovskite structure with a ripple with a periodicity of 50.6 Å occurring in the inorganic slab diagonally to the [101] direction of the basic unit cell. This leads to an increase of Pb–I–Pb angles along the direction of the wave. Generally, both series show larger in-plane bond angles resulting from the additional bulkiness of the spacers compensating for the MA's small size. Larger bond angles have been shown to decrease the bandgap which is seen here with the bulkier IBA leading to both larger in-plane angles and lower bandgaps except for n = 2, in which the modulated structure has a lower bandgap because of its larger Pb–I–Pb angles. Photo-response was tested for the n = 4 compounds and confirmed, signaling their potential use in solar cell devices. We made films using an MACl additive which showed good crystallinity and preferred orientation according to grazing-incidence wide-angle scattering (GIWAXS). As exemplar, the two n = 4 samples were employed in devices with champion efficiencies of 8.22% and 7.32% for IBA and IAA, respectively.