Dr. Paramesh Chandra

Selected publications

1. Morphology controlled $(CH_3NH_3)_3Bi_2Cl_9$ thin film for lead free perovskite solar cell

   Chandra, Paramesh, and Mandal, Swapan K.

   Physica B: Condensed Matter Nov 2021

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   Traditional perovskite solar cells have made tremendous progress in terms of efficiency in the past few years but the presence of toxic lead (Pb) has restricted their commercialization. We report here a process to fabricate MABiCl perovskite thin film based solar cell. The process shows some intriguing outcomes like uniform surface morphology of the perovskite layer, high open-circuit voltage and good fill-factor. The film shows improved uniform morphology and surface coverage with flakes (dimension ˜ 570 nm × 360 nm, thickness   100–200 nm. The solar cell device shows an open-circuit voltage of about 496 mV and a fill factor 0.55. The improved morphology of the perovskite layer with reduced number of defects and charge traps possibly decreases the probability of recombination of photoexcited charge carriers. The result indicates that the process can be a good alternative to prepare lead free perovskite solar cells with improved performance.

   @article{chandra_morphology_2021,
     title = {Morphology controlled $$(CH_3NH_3)_3Bi_2Cl_9$$ thin film for lead free perovskite solar cell},
     volume = {625},
     copyright = {All rights reserved},
     issn = {09214526},
     doi = {10.1016/j.physb.2021.413536},
     number = {April 2021},
     journal = {Physica B: Condensed Matter},
     author = {Chandra, Paramesh and Mandal, Swapan K.},
     month = nov,
     year = {2021},
     note = {Publisher: Elsevier B.V.},
     keywords = {Solar cell, Lead-free perovskite, lead-free perovskite, Dip coating, Photov},
     pages = {413536},
     preview = {physicab.png}
   }

2. Appl. Phys. A

   A dielectric study of Br-doped lead-free methylammonium bismuth chloride $(CH_3NH_3)_3Bi_2Br_xCl_9-x$

   Chandra, Paramesh, Saha, Saroj, and Mandal, Swapan K.

   Applied Physics A Jun 2022

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   We report here the synthesis and dielectric characteristics of lead-free methylammonium bismuth chloride (MABiCl) and bromine (Br) doped methylammonium bismuth chloride (MABiBrCl) powders. The dielectric characteristics of the samples (pressed powder pellet) measured in the frequency range 1 Hz to 1 MHz and temperature range 333–403 K indicate complex electrical transport in these halide perovskite materials. We have observed that the transport is dominated by longrange hopping of carriers and localized charges above and below a critical frequency respectively. The experimental data are fitted with the theoretical models considering grains, grain boundary, and contacts effects and made a comprehensive analysis. The activation energy obtained from ac electrical conductivity measurements is found to be relatively higher for the Br doped MABiBrCl than undoped MABiCl, which might explain some of the properties reported on solar cells and optoelectronic devices.

   @article{chandra_dielectric_2022,
     title = {A dielectric study of Br-doped lead-free methylammonium bismuth chloride $$(CH_3NH_3)_3Bi_2Br_xCl_9-x$$},
     volume = {128},
     copyright = {All rights reserved},
     issn = {0947-8396, 1432-0630},
     doi = {10.1007/s00339-022-05677-9},
     language = {en},
     number = {6},
     urldate = {2022-06-01},
     journal = {Applied Physics A},
     author = {Chandra, Paramesh and Saha, Saroj and Mandal, Swapan K.},
     month = jun,
     year = {2022},
     keywords = {Chemical synthesis, Dielectric relaxation, Impedance spectroscopy, Perovskite},
     pages = {541},
     preview = {apa.png}
   }

3. Mater. Today

   Frequency and temperature-dependent dielectric characteristics of lead-free Br doped perovskites $(CH_3NH_3)_3Bi_2Cl_9 and (CH_3NH_3)_3Bi_2Br_xCl_9-x$

   Chandra, Paramesh, Saha, Saroj, and Mandal, Swapan

   Materials Today: Proceedings Jun 2022

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   We report the synthesis and dielectric characteristics of lead-free methylammonium bismuth chloride (MABiCl) and Br doped methylammonium bismuth chloride (MABiBrCl) in powder form. The morphology of the samples showed growth of large flakes with large surface area. The band gaps of the perovskites are obtained from optical absorption data. The dielectric characteristics of the samples were measured in the frequency range 1 Hz to 1 MHz and temperature range 100–300 K. The data shows a complex electrical transport in these halide perovskite materials. The dielectric permittivity data shows the existence of a critical temperature at which the material undergoes a structural phase transition. The transition temperature is found to be 270 K and 266 K for MABiCl and MABiBrCl respectively. The results can be explained by certain change in orientation of methyl-ammonium (MA) ions as the temperature is increased.

   @article{chandra_frequency_2022,
     title = {Frequency and temperature-dependent dielectric characteristics of lead-free Br doped perovskites $$(CH_3NH_3)_3Bi_2Cl_9$$ and $$(CH_3NH_3)_3Bi_2Br_xCl_9-x$$},
     author = {Chandra, Paramesh and Saha, Saroj and Mandal, Swapan},
     date = {2022-07-06},
     doi = {10.1016/j.matpr.2022.06.413},
     journal = {Materials Today: Proceedings},
     note = {Journal Abbreviation: Materials Today: Proceedings
     		Publication Title: Materials Today: Proceedings},
     preview = {matodayproc.png}
   }

4. Observation of Negative Photoconductivity in $(CH_3NH_3)_3Bi_2(Br_xCl_1–x)_9$: Correlating Ion Migration, Stability, and Efficiency in Mixed Halide Perovskite Solar Cell

   Chandra, Paramesh, and Mandal, Swapan Kumar

   The Journal of Physical Chemistry C Nov 2023

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   Electric field and light induced ion migration resulting in poor stability is a key hindrance for the development of perovskite solar cells and devices. Methods to identify the pathways of ion migration and subsequently to develop strategies to suppress them are prerequisites to develop perovskite solar cells with improved stability and high efficiency. In this report, we probe ion migration through the observation of negative photocurrent (I) measured by temperature (100−283 K) dependent transient photocurrent response character- istics (I−t) as well as current−voltage (I−V) characteristics under dark and light conditions. Controlled experiments are carried out on lead (Pb)-free hybrid perovskite (CH3NH3)3Bi2(BrxCl1−x)9 (where x = 0, 0.33, 0.44, 0.55, 0.66) samples with varying Br/Cl ratio. The mixed halide system is found to have the lowest bandgap of 2.557 eV corresponding to bromine content x = 0.44. Incorporation of bromine has a visible effect on the flake-like microstructures of the perovskite materials. While, the I−V characteristics confirmed the ion migration and phase segregation of halide ions and their irreversibility in the system, the I−t profiles showed the existence of an induced electric field acting in the direction opposite to the applied field due to the migration of halide ions and creation of halide vacancies, resulting in a negative photocurrent. The I−t profiles are found to be reversible and strongly dependent on temperature as well as the Br/Cl ratio. I−V characteristics under light illumination also display hysteresis behavior, the effect of which gets reduced with the increase in bromine content. The photocurrent hysteresis and its irreversibility upon change in scanning direction of the applied electric field is believed to be arising out of ion migration dominant in perovskite materials. A comprehensive analysis has been made to infer the charge transfer process and ion migration in the mixed halide system contributing to the stability and efficiency of perovskite solar cells and devices.

   @article{Chandra_2023,
     title = {Observation of Negative Photoconductivity in $$(CH_3NH_3)_3Bi_2(Br_xCl_{1–x})_9$$: Correlating Ion Migration, Stability, and Efficiency in Mixed Halide Perovskite Solar Cell},
     volume = {127},
     issn = {1932-7455},
     doi = {10.1021/acs.jpcc.3c06427},
     number = {47},
     journal = {The Journal of Physical Chemistry C},
     publisher = {American Chemical Society (ACS)},
     author = {Chandra, Paramesh and Mandal, Swapan Kumar},
     year = {2023},
     month = nov,
     pages = {23109-23121},
   }