Anubhav Raghav - Academia.edu (original) (raw)

Papers by Anubhav Raghav

Research paper thumbnail of Charge carrier dynamics study and morphology optimization in solvent annealed CH3NH3PbI3 perovskite for air processed stable solar cell application

Chemical Physics, 2019

We report room temperature excitation intensity dependent charge carrier dynamics in solvent-anne... more We report room temperature excitation intensity dependent charge carrier dynamics in solvent-annealed organo-metal halide perovskite semiconductor CH3NH3PbI3 thin film using steady state and time resolved photoluminescence studies. The average lifetime of these solvent annealed films does not vary significantly with excitation fluence confirming the formation of almost defect free perovskite crystallites. The photocarrier dynamics are well described by a simple rate equation. The local reduction of shallow trap densities as observed in PL dynamics was correlated with scanning electron microscopy (SEM) and X-ray spectroscopy. The observed photophysical investigation and morphology study suggests that anti-solvent method as a potential approach for CH3NH3PbI3 perovskite solar cell fabrication under ambient condition. A prototype all air processed anti-solvent method based stable perovskite device yielded the efficiency of 7.54% with JSC value of 14.21 mA/cm 2 and VOC of 810 mV.

Research paper thumbnail of Controlling morphology ofCH3NH3PbI3perovskite film by dual solvent elimination method

Nano-Structures & Nano-Objects, 2017

Abstract Uniform CH 3 NH 3 PbI 3 perovskite film with lower surface roughness was fabricated by t... more Abstract Uniform CH 3 NH 3 PbI 3 perovskite film with lower surface roughness was fabricated by tuning the dielectric constant ( e r ) of the precursor solvents. The extraction of highly polar solvent over localized area in this dual solvent elimination method (DSEM) leads to larger grain size and better crystallinity at room temperature. The correlated confocal PL and scanning electron microscopy (SEM) depicts minimal distribution in local PL intensity across this uniform film. Photoluminescence spectroscopy and fluorescence microscopy were utilized to probe the underlying photophysics of the perovskite film. The photovoltaic device fabricated in ambient air was found to have efficiency of 6% with J SC value of 12.5 mA and V OC of 900 mV.

Research paper thumbnail of Effect of functional groups on sensitization of dye-sensitized solar cells (DSSCs) using free base porphyrins

Journal of Porphyrins and Phthalocyanines, 2017

Dye-sensitized solar cells (DSSCs) were fabricated with six meso-substituted A[Formula: see text]... more Dye-sensitized solar cells (DSSCs) were fabricated with six meso-substituted A[Formula: see text]B and A[Formula: see text] free base porphyrin dyes having different functional groups, as sensitizers. The two step synthesis and the effect of different functional groups and their positions on the photosensitization properties of these porphyrin dyes are reported. The highest power conversion efficiencies ([Formula: see text] of 3.26%, 2.94% and 2.84% were achieved for the DSSC fabricated using 5,10,15-tris(4[Formula: see text]-pyridyl)-20-(4[Formula: see text]-carboxyphenyl)porphyrin (H[Formula: see text]TriPyMCPP), 5,10,15,20-tetrakis(4[Formula: see text]-aminophenyl)porphyrin (H[Formula: see text]TAPP) and 5-(4[Formula: see text]-pyridyl)-10,15,20-tris(4[Formula: see text]-carboxyphenyl)porphyrin (H[Formula: see text]MPyTriCPP) dyes, respectively. The electron donating amino group is shown to enhance the power conversion efficiency while pyridyl appended porphyrin sensitizers are s...

Research paper thumbnail of Utilization of Naturally Occurring Dyes as Sensitizers in Dye Sensitized Solar Cells

IEEE Journal of Photovoltaics, 2017

Dye sensitized Solar cells (DSSCs) were fabricated with four naturally occurring anthocyanin dyes... more Dye sensitized Solar cells (DSSCs) were fabricated with four naturally occurring anthocyanin dyes extracted from naturally found fruits/ juices (viz. Indian Jamun, Plum, Black Currant and Berries) as sensitizers. Extraction of anthocyanin was done using acidified ethanol. The highest power conversion efficiencies (η) of 0.55% and 0.53% were achieved for the DSSCs fabricated using anthocyanin extracts of blackcurrant and mixed berry juice. Widespread availability of these fruits/juices, high concentration of anthocyanins in them and ease of extraction of anthocyanin dyes from these commonly available fruits render them novel and inexpensive candidates for solar cell fabrication.

Research paper thumbnail of Charge Carrier Dynamics Study and Morphology Optimization in Solvent Annealed CH3NH3PbI3 Perovskite for Air Processed Stable Solar Cell Application

Research paper thumbnail of Controlling morphology ofCH3NH3PbI3perovskite film by dual solvent elimination method

Nano-Structures & Nano-Objects

Research paper thumbnail of Local Optoelectronic Characterization of Solvent-Annealed Lead-Free, Bismuth-Based Perovskite Films

Research paper thumbnail of Morphological and Photophysical Study in Hybrid Ternary Organic Nanoparticles Blends

Research paper thumbnail of Effect of size and charge asymmetry on aggregation kinetics of oppositely charged nanoparticles

Scientific Reports

We report a theoretical and experimental study of the aggregation kinetics of oppositely charged ... more We report a theoretical and experimental study of the aggregation kinetics of oppositely charged nanoparticles. Kinetic Monte Carlo simulations are performed for symmetric, charge-asymmetric and size-asymmetric systems of oppositely charged nanoparticles. Simulation results show that both the weight and number average aggregate size kinetics exhibit power law scaling with different exponents for small and intermediate time of evolution. The qualitative behavior of the symmetric and the size asymmetric system are the same, but the charge asymmetric system shows anomalous behavior for intermediate to high particle concentrations. We also observe a strong dependence of power law exponents on the particle concentration. Radius of gyration of the cluster that indicates how nanoparticles inside a cluster are distributed around the center of mass of the cluster shows a nonmonotonic time evolution with pronounced peak at higher particle concentration. The dependence of particle concentration on aggregation kinetics as observed by predictive numerical simulation is further verified experimentally by monitoring the time evolution of aggregate size of nanoparticles assemblies of Poly (methacrylic acid) (PMMA) nanoparticles functionalized with oppositely charged ligands. These size and charge tunable asymmetric polymeric nanoparticles were synthesized by modified miniemulsion technique. The integrated approach for studying nanoparticles aggregation as described here renders new insights into super structure formation and morphology optimization which can be potentially useful in the design of new materials, such as organic photovoltaics. Bottom-up self-assembly to build functional complex structures using nanoparticles (NP) as building blocks has received tremendous research attention in last few years 1. These self-assembled structures can be effectively used in various industrial applications such as waste water treatment 2 , sensing 3 , drug delivery 4 , NP based solar cells 5 , etc. Tuning of NP shape, size, interaction etc. gives a control over the super structure formed by them 6-9. Aggregation of NPs is strongly affected by the competition of inter-particle interactions such as van der Waals, electrostatic, and magnetic interactions, which in turn depends on the material property of NPs, dielectric constant of solvent, temperature, pH, and presence of external fields. Out of various inter-particle interactions, electrostatic interactions are somewhat unique, because they are long-ranged and, can be either attractive or repulsive. Also, their interaction strength and interaction range can be easily tuned by varying the charge on the NPs and ionic strength, respectively 9-13. Such tunability of electrostatic interaction has many implications on the aggregation kinetics and self-assembly of oppositely charged NPs 14. Aggregation of nanoparticles can be broadly classified into homo-aggregation and hetero-aggregation 15 ; homo-aggregation is the aggregation of the NPs with identical characteristics, whereas in hetero-aggregation, NPs with different physical and chemical properties aggregates to form clusters. Naturally, hetero-aggregation is more complex and is therefore not yet completely understood 15-18. Recent experiments on the synthesis of NPs of different size, charge, and chemical composition have provided new insight into the mechanisms of aggregation processes 19-21. Experimentally aggregation kinetics of NPs is studied using Dynamic Light Scattering(DLS) 22,23 , time-resolved DLS 24 and Small-angle Neutron Scattering(SANS) 25,26. Charged NPs hetero-aggregation has received much more attention due to ease of controlling the charge on NPs and its application in ionic colloidal crystals, organic optoelectronics and flocculation techniques 27-32. However, synthesis of monodisperse and precisely charged NPs at large scale with high reproducibility is always challenging and needs in-depth theoretical understanding and

Research paper thumbnail of Charge carrier dynamics study and morphology optimization in solvent annealed CH3NH3PbI3 perovskite for air processed stable solar cell application

Chemical Physics, 2019

We report room temperature excitation intensity dependent charge carrier dynamics in solvent-anne... more We report room temperature excitation intensity dependent charge carrier dynamics in solvent-annealed organo-metal halide perovskite semiconductor CH3NH3PbI3 thin film using steady state and time resolved photoluminescence studies. The average lifetime of these solvent annealed films does not vary significantly with excitation fluence confirming the formation of almost defect free perovskite crystallites. The photocarrier dynamics are well described by a simple rate equation. The local reduction of shallow trap densities as observed in PL dynamics was correlated with scanning electron microscopy (SEM) and X-ray spectroscopy. The observed photophysical investigation and morphology study suggests that anti-solvent method as a potential approach for CH3NH3PbI3 perovskite solar cell fabrication under ambient condition. A prototype all air processed anti-solvent method based stable perovskite device yielded the efficiency of 7.54% with JSC value of 14.21 mA/cm 2 and VOC of 810 mV.

Research paper thumbnail of Controlling morphology ofCH3NH3PbI3perovskite film by dual solvent elimination method

Nano-Structures & Nano-Objects, 2017

Abstract Uniform CH 3 NH 3 PbI 3 perovskite film with lower surface roughness was fabricated by t... more Abstract Uniform CH 3 NH 3 PbI 3 perovskite film with lower surface roughness was fabricated by tuning the dielectric constant ( e r ) of the precursor solvents. The extraction of highly polar solvent over localized area in this dual solvent elimination method (DSEM) leads to larger grain size and better crystallinity at room temperature. The correlated confocal PL and scanning electron microscopy (SEM) depicts minimal distribution in local PL intensity across this uniform film. Photoluminescence spectroscopy and fluorescence microscopy were utilized to probe the underlying photophysics of the perovskite film. The photovoltaic device fabricated in ambient air was found to have efficiency of 6% with J SC value of 12.5 mA and V OC of 900 mV.

Research paper thumbnail of Effect of functional groups on sensitization of dye-sensitized solar cells (DSSCs) using free base porphyrins

Journal of Porphyrins and Phthalocyanines, 2017

Dye-sensitized solar cells (DSSCs) were fabricated with six meso-substituted A[Formula: see text]... more Dye-sensitized solar cells (DSSCs) were fabricated with six meso-substituted A[Formula: see text]B and A[Formula: see text] free base porphyrin dyes having different functional groups, as sensitizers. The two step synthesis and the effect of different functional groups and their positions on the photosensitization properties of these porphyrin dyes are reported. The highest power conversion efficiencies ([Formula: see text] of 3.26%, 2.94% and 2.84% were achieved for the DSSC fabricated using 5,10,15-tris(4[Formula: see text]-pyridyl)-20-(4[Formula: see text]-carboxyphenyl)porphyrin (H[Formula: see text]TriPyMCPP), 5,10,15,20-tetrakis(4[Formula: see text]-aminophenyl)porphyrin (H[Formula: see text]TAPP) and 5-(4[Formula: see text]-pyridyl)-10,15,20-tris(4[Formula: see text]-carboxyphenyl)porphyrin (H[Formula: see text]MPyTriCPP) dyes, respectively. The electron donating amino group is shown to enhance the power conversion efficiency while pyridyl appended porphyrin sensitizers are s...

Research paper thumbnail of Utilization of Naturally Occurring Dyes as Sensitizers in Dye Sensitized Solar Cells

IEEE Journal of Photovoltaics, 2017

Dye sensitized Solar cells (DSSCs) were fabricated with four naturally occurring anthocyanin dyes... more Dye sensitized Solar cells (DSSCs) were fabricated with four naturally occurring anthocyanin dyes extracted from naturally found fruits/ juices (viz. Indian Jamun, Plum, Black Currant and Berries) as sensitizers. Extraction of anthocyanin was done using acidified ethanol. The highest power conversion efficiencies (η) of 0.55% and 0.53% were achieved for the DSSCs fabricated using anthocyanin extracts of blackcurrant and mixed berry juice. Widespread availability of these fruits/juices, high concentration of anthocyanins in them and ease of extraction of anthocyanin dyes from these commonly available fruits render them novel and inexpensive candidates for solar cell fabrication.

Research paper thumbnail of Charge Carrier Dynamics Study and Morphology Optimization in Solvent Annealed CH3NH3PbI3 Perovskite for Air Processed Stable Solar Cell Application

Research paper thumbnail of Controlling morphology ofCH3NH3PbI3perovskite film by dual solvent elimination method

Nano-Structures & Nano-Objects

Research paper thumbnail of Local Optoelectronic Characterization of Solvent-Annealed Lead-Free, Bismuth-Based Perovskite Films

Research paper thumbnail of Morphological and Photophysical Study in Hybrid Ternary Organic Nanoparticles Blends

Research paper thumbnail of Effect of size and charge asymmetry on aggregation kinetics of oppositely charged nanoparticles

Scientific Reports

We report a theoretical and experimental study of the aggregation kinetics of oppositely charged ... more We report a theoretical and experimental study of the aggregation kinetics of oppositely charged nanoparticles. Kinetic Monte Carlo simulations are performed for symmetric, charge-asymmetric and size-asymmetric systems of oppositely charged nanoparticles. Simulation results show that both the weight and number average aggregate size kinetics exhibit power law scaling with different exponents for small and intermediate time of evolution. The qualitative behavior of the symmetric and the size asymmetric system are the same, but the charge asymmetric system shows anomalous behavior for intermediate to high particle concentrations. We also observe a strong dependence of power law exponents on the particle concentration. Radius of gyration of the cluster that indicates how nanoparticles inside a cluster are distributed around the center of mass of the cluster shows a nonmonotonic time evolution with pronounced peak at higher particle concentration. The dependence of particle concentration on aggregation kinetics as observed by predictive numerical simulation is further verified experimentally by monitoring the time evolution of aggregate size of nanoparticles assemblies of Poly (methacrylic acid) (PMMA) nanoparticles functionalized with oppositely charged ligands. These size and charge tunable asymmetric polymeric nanoparticles were synthesized by modified miniemulsion technique. The integrated approach for studying nanoparticles aggregation as described here renders new insights into super structure formation and morphology optimization which can be potentially useful in the design of new materials, such as organic photovoltaics. Bottom-up self-assembly to build functional complex structures using nanoparticles (NP) as building blocks has received tremendous research attention in last few years 1. These self-assembled structures can be effectively used in various industrial applications such as waste water treatment 2 , sensing 3 , drug delivery 4 , NP based solar cells 5 , etc. Tuning of NP shape, size, interaction etc. gives a control over the super structure formed by them 6-9. Aggregation of NPs is strongly affected by the competition of inter-particle interactions such as van der Waals, electrostatic, and magnetic interactions, which in turn depends on the material property of NPs, dielectric constant of solvent, temperature, pH, and presence of external fields. Out of various inter-particle interactions, electrostatic interactions are somewhat unique, because they are long-ranged and, can be either attractive or repulsive. Also, their interaction strength and interaction range can be easily tuned by varying the charge on the NPs and ionic strength, respectively 9-13. Such tunability of electrostatic interaction has many implications on the aggregation kinetics and self-assembly of oppositely charged NPs 14. Aggregation of nanoparticles can be broadly classified into homo-aggregation and hetero-aggregation 15 ; homo-aggregation is the aggregation of the NPs with identical characteristics, whereas in hetero-aggregation, NPs with different physical and chemical properties aggregates to form clusters. Naturally, hetero-aggregation is more complex and is therefore not yet completely understood 15-18. Recent experiments on the synthesis of NPs of different size, charge, and chemical composition have provided new insight into the mechanisms of aggregation processes 19-21. Experimentally aggregation kinetics of NPs is studied using Dynamic Light Scattering(DLS) 22,23 , time-resolved DLS 24 and Small-angle Neutron Scattering(SANS) 25,26. Charged NPs hetero-aggregation has received much more attention due to ease of controlling the charge on NPs and its application in ionic colloidal crystals, organic optoelectronics and flocculation techniques 27-32. However, synthesis of monodisperse and precisely charged NPs at large scale with high reproducibility is always challenging and needs in-depth theoretical understanding and