B.Sc: University of Calcutta, 2013
M.Sc: University of Calcutta, 2015
CSIR-UGC-NET (JRF): 2015
Indian Association for the Cultivation of Science, 2016-2022
PostDoc: Weizmann Institute of Science
From Photo-Damage to Self-Healing in Thin Film Pb-Iodide Perovskites: Action at a Distance Yahel Soffer, Dipanwita Roy, Pallavi Singh, David Cahen, Dan Oron Advanced Optical Materials, 2025 Lead halide perovskites (HaPs) have gained much attention, especially for use in photovoltaics and optoelectronic devices. However, stability remains the major roadblock to implementing HaP‐based devices. Self‐healing, the material's intrinsic tendency to recover from damage without any external aid, is observed in HaPs. Yet, understanding of its detailed mechanism is still lacking. Fluorescence recovery after photobleaching and photoluminescence (PL) imaging are used to monitor changes in HaP polycrystalline thin films in both space and time following damage, through the self‐recovery path. Changes in PL outside the excitation spot are identified immediately following photodamage for both CsPbI3 (CsPI), showing photo‐darkening, and MAPbI3 (MAPI), exhibiting photo‐brightening. During self‐healing of the directly illuminated spot, MAPI peripheral fluorescence decreases to its initial level, whereas CsPI exhibits photo‐brightening to above the original level. This can be correlated with processes occurring on two time scales: rapid electronic defect passivation and slower ion migration. Investigating PL dynamics under intense laser damage demonstrates that changes to PL can be attributed to a combination of charge carrier trapping and trap removal in the early stages and ion migration and redox reactions in later stages. The understanding of spatio‐temporal dynamics of damage and self‐healing can promote longevity of HaP‐based devices.
Postsynthesis Spontaneous Coalescence of Mixed-Halide Perovskite Nanocubes into Phase-Stable Single-Crystalline Uniform Luminescent Nanowires Bapi Pradhan, Aamir Mushtaq, Dipanwita Roy, Sumanta Sain, Bidisa Das, et al. Journal of Physical Chemistry Letters, 2019 All inorganic mixed-halide perovskite, CsPb(Br xI1- x)3 (0 ≤ x ≤ 1), nanocrystals possess tunable photoluminescence with high quantum yield in the visible window. However, the photoluminescence degrades rapidly with postsynthetic aging due to the spontaneous ion separation and phase instability. Here we show that the postsynthetic aging of CsPb(Br xI1- x)3 nanocubes spontaneously forms highly uniform single-crystalline nanowires with a diameter of 9 ± 0.5 nm and length of up to several micrometers. The nanowires show bright photoluminescence with an absolute photoluminescence quantum yield of 41%. Rietveld refinement identifies the stable orthorhombic phase of the nanowires, implying a phase transition from the cubic crystallographic phase of the nanocubes during the morphology evolution. Transient absorption spectroscopy reveals a faster excited-state decay dynamic with a large exciton delocalization length in 1D nanowires. Our findings elucidate the insights into the postsynthesis morphology evolution of mixed-halide perovskite nanocrystals leading to luminescent nanowires with excellent crystal phase stability for potential optoelectronic applications.
Solution phase synthesis of large-area ultra-thin two dimensional layered Bi2Se3: role of Cu-intercalation and substitution Bapi Pradhan, Amit Dalui, Susmita Paul, Dipanwita Roy, Somobrata Acharya Materials Research Express, 2019 Intercalation of high densities of guest species without affecting the host lattice is challenging. Here we report on a general solution-based synthesis route to intercalate high densities of zero-valent copper into layered Bi2Se3 nanosheets at room temperature. We develop a solution phase synthesis route to design large area single-crystalline two-dimensional ultrathin Bi2Se3 nanosheets with micron dimensions. Layered Bi2Se3 nanosheets possess rhombohedral crystal structure where the Bi and Se hexagonal planes remain in close stacked configuration forming quintuple layers along the c-direction. The coupling between two quintuple layers is predominantly van der Waals type, which allows intercalating smaller guest zero-valent copper within the layers of Bi2Se3 nanosheets. Such intercalation of guest species without affecting the lattices of Bi2Se3 is challenging considering the change in oxidation state of copper, which limits the intercalant concentration. Additionally, we show that the use of CuI-amine complex at high temperature reaction conditions yields CuI substituted CuI-Bi2Se3 nanosheets disrupting the host lattice of Bi2Se3 nanosheets. We have explored the role of intercalation and substitution on the electronic properties of pristine Bi2Se3 nanosheets. Development of new synthetic strategy for the synthesis of ultra-thin larger area 2D layered Bi2Se3 nanosheets and understanding the role of metal intercalation and substitution hold promises for fundamental understanding and energy related applications.
