Sudhakar Narra

Sudhakar Narra
National Yang Ming Chiao Tung University · Department of Applied Chemistry

PhD
Ultrafast Spectroscopy and Dynamics of Perovskites, Photocatalytic, and 2D Materials

About

32
Publications
7,473
Reads
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788
Citations
Citations since 2016
28 Research Items
778 Citations
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
Introduction
Sudhakar's research interests are structural studies, dynamics and electric field effects on functional materials using ultrafast optical spectroscopy.
Additional affiliations
June 2022 - present
National Yang Ming Chiao Tung University
Position
  • Assitant Research Fellow
August 2015 - May 2022
National Chiao Tung University
Position
  • PostDoc Position
May 2015 - July 2015
National Chiao Tung University
Position
  • Research Assistant
Education
September 2008 - September 2014
National Chiao Tung University
Field of study
  • Physical Chemistry
July 2006 - April 2008
Banaras Hindu University
Field of study
  • Chemistry

Publications

Publications (32)
Article
Back electron transfer (BET) is one of the important processes that govern the decay of generated ion pairs in intermolecular photoinduced electron transfer reactions. Unfortunately, a detailed mechanism of BET reactions remains largely unknown in spite of their importance for the development of molecular photovoltaic structures. Here, we examine t...
Article
The effects of additives SnF2 (10 %) and EDAI2 (1 %) on the dynamics of carrier relaxation of formamidinium tin triiodide (FASnI3) perovskite were studied using femtosecond transient absorption spectra (TAS) with excitation at 600 and 870 nm. The TAS were analyzed according to a parallel sequential kinetic model with a global fit through singular-v...
Article
Femtosecond transient absorption spectral (TAS) investigations were performed to understand the carrier relaxation mechanism for perovskite nanocrystals Cs1-xFAxPbBr3 (CF, x = 0.45) and CsPbBr3 (CS), which served as efficient photocatalysts for splitting of CO2 into CO and O2 in the absence of water. Upon light irradiation for 12 h, formation of de...
Article
We designed an S-heterojunction system with a perovskite nanocrystal, Cs1–xFAxPbBr3 (CF), coupled with a bismuth oxyiodide (BiOI) nanosheet to form a perovskite heterojunction (PHJ) photocatalyst. On the basis of femtosecond transient absorption measurements, the pristine CF sample has two charge recombination periods, 100 and 900 ps, corresponding...
Article
We deposited a smooth and uniform tin-perovskite layer on a hydrophobic conducting polymer, (bis (4-phenyl) (2,4,6-trimethylphenylamine) (PTAA), on modification of the PTAA surface with an organic ammonium salt, phenylethylammonium iodide (PEAI), according to a two-step approach. We found that π-π interaction between the phenyl rings of PTAA and PE...
Article
A simple one-pot synthesis of stable red-emitting perovskite nanocrystals (PeNCs) involved the addition of Cs-oleate, formamidinium bromide (FABr) and organic ammonium iodide salts (represented as LnI,n= 1-5) to a hot flask containing oleic acid (OA), oleylamine (OLA) and PbI2. The crystal structures of these PeNCs that are rich in halide on the su...
Article
Full-text available
Overcoming the issue of stability of tin‐based perovskites is a main challenge for the commercial development of lead‐free perovskite solar cells. To tackle this problem, a new organic cation, azetidinium (AZ), is incorporated into the crystal structure of formamidinium tin triiodide (FASnI 3 ) to form mixed cation perovskite AZ x FA 1‐ x SnI 3 . A...
Article
Full-text available
Steady‐state and time‐resolved photoluminescence (PL) and electrophotoluminescence (E‐PL) have been recorded for bulk heterojunction samples of thin films of regio‐regular poly(3‐hexylthiophene) (P3HT) and methyl [6,6]‐phenyl‐C61‐butanoate (PCBM). The PL spectra of the bulk heterojunction samples showed a monotonic decrease of PL quantum yield with...
Article
The structural and optical properties of pristine and photoactivated surfaces of facet [001] of 2D BiOI nanoplatelet powders synthesized with an antisolvent method were studied using X-ray diffraction (XRD), a scanning electron microscope, X-ray photoelectron spectra (XPS), visible–near infrared (vis–NIR) absorption, and transient absorption spectr...
Article
Full-text available
To solve the toxic issue for new-generation photovoltaic applications, tin-based perovskite solar cells are a promising alternative to their lead counterparts, but they suffer from poor stability because of their tendency to exhibit tin oxidation. Herein we report a new sequential method of deposition based on solution processing using hexafluoro-2...
Article
Tin-based perovskites degrade rapidly upon interaction with water and oxygen in air because Sn-I bonds are weak. To address this issue, we developed novel tin perovskites, FASnI(3-x)(SCN) x (x = 0, 1, 2, or 3), by employing a pseudohalide, thiocyanate (SCN-), as a replacement for halides and as an inhibitor to suppress the Sn2+/Sn4+ oxidation. The...
Article
Alcohol-based bifunctional ammonium cations, 2-hydroxyethylammonium (HEA+), HO(CH2)2NH3+, were introduced into formamidinium (FA+) tin-based perovskites (HEAxFA1-xSnI3; x = 0 – 1) to absorb light in carbon-based mesoscopic solar cells. We found that HEA+ cations play a key role to control the crystal structures; the lattice structures altered from...
Article
Full-text available
Electroabsorption (E-A) spectra of lead halide perovskites, that is, CH3NH3PbI3–xBrx (x = 0–3), which show large spectral shift depending on the ratio between iodine and bromide, have been measured. By analyzing E-A spectra with the integral method, spectral shape of the absorption spectra for the first exciton band and binding energy of exciton ha...
Article
Full-text available
Photoluminescence (PL) of a nanocrystalline film of methylammonium lead iodide perovskite (MAPbI3 sandwiched between an electrode of a fluorine-doped tin-oxide (FTO) layer and an insulating film of polymethyl methacrylate (PMMA) is found to increase and decrease significantly with the application of external electric field (Fext), depending on the...
Article
Reduced graphene oxides (rGO) are synthesized via reduction of GO with reducing agents as a hole-extraction layer for high-performance inverted planar heterojunction perovskite solar cells. The best efficiencies of power conversion (PCE) of these rGO cells exceed 16%, much greater than those made of GO and poly(3,4-ethenedioxythiophene):poly(styren...
Article
We report the effect of thickness of a film consisting of a compact layer of TiO2 produced via atomic-layer deposition (ALD) for mesoporous perovskite solar cells (PSC) with a n-i-p configuration. Uniform and pinhole-free TiO2 films of thickness from 10-400 nm were deposited on fluorine-doped tin-oxide substrates using ALD. The device performance o...
Article
Full-text available
Mixing graphene oxide (GO) with CH3NH3PbI3 (PSK) in varied proportions (0.025, 0.05 and 0.075 mg mL-1) and using GO nanosheets as a p-type electrode for devices with a layer-by-layer thin-film configuration ITO/GO/PSK:GO/PCBM/Ag produced hybrid composite perovskite solar cells. The efficiency of power conversion (PCE) of the device prepared with GO...
Article
We report a simple synthetic approach to grow uniform CH3NH3PbI3 perovskite (PSK) layers ‎free of pinholes via varied portions of silver iodide (AgI) added to the precursor solution. The ‎powder XRD results exhibited the improvement of crystallinity for devices with AgI additive, ‎however, PbI2 residue was observed at greater AgI concentrations (1...
Article
To produce mesoscopic carbon-electrode-based solar cells free of a hole-conduction layer, we developed a simple one-step drop-cast method (temperature 20 °C, relative humidity 50%) to grow uniform and compact perovskite nanocrystals via slow crystallization (SC). X-ray diffraction (XRD) results indicated that perovskite nanocrystals produced inside...
Article
CoOx is a promising hole-extracting layer (HEL) for inverted planar perovskite solar cells with device configuration ITO/CoOx/CH3NH3PbI3/PCBM/Ag. The devices fabricated according to a simple solution procedure showed the best photovoltaic performance attaining power conversion efficiency (PCE) 14.5 % under AM 1.5 G one-sun irradiation, which is sig...
Article
We report the synthesis and characterization of alloyed Sn-Pb methylammonium mixed-halide perovskites (CH3NH3SnyPb1-yI3-xClx) to extend light harvesting toward the near infrared region for carbon-based mesoscopic solar cells free of organic hole-transport layers. The proportions of Sn in perovskites are well controlled with mixing tin chloride (SnC...
Article
Solar cells based on organometal-halide perovskites such as CH3NH3PbI3 have emerged as a promising next-generation photovoltaic system, but the underlying photophysics and photochemistry remain to be established because of the limited availability of methods to implement the simultaneous and direct measurement of various charge carriers and ions th...
Article
Low-lying excited triplet states of aromatic carbonyl compounds exhibit diverse photophysical and photochemical properties of fundamental importance. Despite tremendous effort in studying those triplet states, the effects of substituents and solvents on the energetics of the triplet manifold and on photoreactivity remain to be fully understood. We...
Article
Low-lying excited electronic states of an important class of molecules known as push-pull chromophores are central to understanding their potential nonlinear optical properties. Here we report that a combination of high-sensitivity nanosecond time-resolved dispersive IR spectroscopy and DFT calculations on p-nitroaniline (PNA), a prototypical push-...

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Projects (3)
Project
All printable perovskite solar cells toward large area and understand the crystallization behavior of different kinds of perovskite crystals.