Browsing by Author "Li, Wenbin"

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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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    Understanding structural dynamics using in-situ correlated measurements for halide perovskites
    (2023-11-03) Li, Wenbin; Mohite, Aditya D
    Organic-inorganic hybrid halide perovskites have emerged as a new semiconductor platform for next-generation optoelectronic devices. The standard “3D” perovskite materials, with chemical formula ABX3, where A represents an organic cation, B represents a metal, and X represents a halide, have shown immense promises due to its high power conversion efficiencies (compared to silicon). However, their intrinsic instability under realistic operating conditions limits their implementation in optoelectronic technologies of the future. On the other hand, layered two-dimensional (2D) perovskites, a subclass of hybrid perovskites, have demonstrated stability performances closer to industrial standard but with a lower efficiencies. These materials are composed of large organic molecules which are inserted into their lattice, breaking the 3D perovskite structure into layered slabs of controllable thickness and composition. In this thesis, we will explore the advances in fabricating 2D and 3D halide perovskite materials for high performance optoelectronic applications and understand the structural dynamics of halide perovskites during thin-film formation and external stimuli (realistic operating conditions). This dissertation is split into 4 main parts. First, I will be discussing the background of halide perovskite (both 2D and 3D) through a structure standpoint. Second, I will be reporting a unique approach to synthesize phase pure high n value 2D perovskite single crystals that utilizes machine learning. In addition, I will discuss a novel fabrication process of synthesizing phase pure 2D perovskite thin-films for solar cell application. Third, we will continue the work by discussing the durability of the 2D perovskite devices and the structural and electronic behaviors under light illumination. Lastly, we will tackle the problem of fabricating phase stable "black” alpha-phase FAPbI3 perovskite using 2D perovskite crystals as additives.
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    Understanding the structural properties in two-dimensional halide perovskites under external stimuli
    (2021-08-23) Li, Wenbin; Mohite, Aditya D.; Kono, Junichiro; Wehmeyer, Geoff
    Understanding the structural and electrical behaviors of organic-inorganic (hybrid) halide perovskites under practical environments is critical for building an efficient and stable optoelectronic device. In this thesis, we report a light-activated interlayer contraction in 2D hybrid halide perovskite. This effect is reversible and is strongly dependent on the structural phase and interlayer distance. X-ray photoelectron spectroscopy and density function theory simulation suggest that photogenerated hole carriers are accumulating at the inter-slab iodide atoms which results in the enhancement of interlayer I---I interactions across the organic barrier. In-situ structural (device) and transport (space charge limited current-SCLC) measurements directly correlate the light-induced interlayer contraction to the onset of a three-fold increase in carrier mobility and conductivity. Furthermore, light intensity dependent SCLC measurement reveals a percolation based mechanism for the enhancement of the charge transport. The increase in transport properties boost the photovoltaic efficiency of Dion-Jacobson 2D n=4 perovskite solar cells from 15.6% to 18.3%.