Taketo Handa

I'll be giving a talk at the CQP seminar at NYU! Actually my first visit to NYU!

Collaborative work published fromJACS!

Collaborative work published from PRB!

I gave an online class to freshmen at Meizen High School, Japan (my alma mater, actually!), which was so much fun! While the class was on my current research projects, I had various sharp questions and comments, which made me feel like I was in the Q&A session of a conference talk. It's always fun and inspiring to talk with people with fresh minds and very fundamental questions!

I gave a talk at the MRSEC symposium on our recent progeress on the THz spectroscopy x 2D materials. (As always,) it was a quite active discussion and got various critical feedvbacks!

Our paper studying the quasiparticles in photoexcited TMDC monolayers with THz spectroscopy has been published in Sci. Adv.! Due to their ultimately thin nature and consequent very large exciton binding energies, photoexcitation of TMDCs has been considered to result in the formation of charge-neutral excitons. Our work reveals the presence of large number of free charge carriers and its relation to defect states. One of the most fascinating aspects of this project is the ability to study the properties of atomically thin materials, thinner than a nanometer, using far-field THz waves with wavelengths on the order of a millimeter. This comprehensive work was made possible through exceptional collaboration with groups at Columbia and Max Planck Institute for Polymer Research. I deeply appreciate this collaboration!

Collaborative work was posted to the arXiv!

The new year has started! I'll try my best so I can fill this page with exciting updates!

Collaborative work now out from Nat. Commun.!

Collaborative work posted to the arXiv!

Collraborative work on primary Pair Density Wave (PDW) formation with the Pasupathy group (Columbia & Brookhaven National Lab) was published in Nature!

Our manuscript is posted to the arXiv where we thoroughly study quasiparticles in photoexcited single-crystal, monolayer TMDCs using ultrafast THz conductivity spectroscopy!

Our short review paper (work at Kyoto) was published in ECS J. Solid State Sci. Technol., summarizing our perspective on spectroscopic characterization of solar cell materials and its relation to the photovoltaic performance of a corresponding device! See more discussion in Research Page (coming soon!).

Collaborative work (done at Kyoto) was published in Solar RRL! We report the successful fabrication of deformation-free, ultrathin flexible perovskite solar cells. The key to success was effectively mitigating the strain typically arising in an ITO layer by forming a double ITO layer.

Attended APS March Meeting @ Las Vegas! Enjoyed the city with group members and ran into my friend from high school...－ in-person meeting is great!

EFRC collaborative meeting

I gave a seminar at the Pro-QM Zeminar, having a lot of fun with in-person active discussion!

Our work, with the great collaoration with the Nuckolls, Roy, and Berkelbach groups was published in J. Phys. Chem. C!

We experimentally and theoretically studied optical responses and electronic structures of 2D superatomic solid made of atomically-precise [Re6Se8] clusters. We observe linearly polarized PL emissions whose direction strongly depends on the temperature. The two distinct directions of PL emissions observed at low and high temperatures correspond, respectively, to the asymmetric inter-cluster bonding directions within the 2D plane. With DFT and TDDFT, we discuss the microscopic origins of the observations and, more broadly, how the electronic structure of individual clusters evolves when they are fused together. Together with the findings on the C60-based superatomic solid, these results point to the possibility of strategic hierarchal design of superatomic solid with targeted properties.

Collaborative work at Columbia (led by the Roy group) was published in Nature, reporting the synthesis and evaluation of materials properties of graphullerene, a two-dimensional crystalline polymer of C60! We, the XYZ group, contributed to far-field visible spectroscopic studies. Spectroscopic findings include a brightening of excitons in graphullerene (compared to individual C60 clusters) due to the interlcuster-bonding-induced change in band-edge electornic structure, the observation of PL down to bilayer, and polarizaed PL emission reflecting the assymetric intercluser bonding within the 2D plane.

Collaboration work done at Kyoto University was published in ACS Appl. Energy Mater.!

Anomolous drop of JPY-USD these days...

I gave a talk online for the JSAP Autumn Meeting on correlated luminescence and ferroelectricity in metal-free ferroelectric halide perovskite (Sep-23 at Session 12.3).

Collaborative work was published in Physical Review Materials! Coherent phonon spectroscopy revealed the electron-soft TO phonon coupling in a typical ferroelectric semiconductor SbSI.

Our paper was published in J. Chem. Phys.! In photovoltaic research, the determination of charge carrier lifetime using pulse-excitation time-resolved techniques constitutes invaluable means for evaluating material properties toward photovoltaic application. Despite its wide use, there has yet been concise discussion on how one can relate the lifetime determined by pulse-excitation measurements to the steady-state carrier lifetime and density that will be realized under cw excitation (actual operation condition). We propose in this paper a simple analysis procedure that enables predicting the steady-state carrier properties and thus relevant photovoltaic performance in a solar cell under cw 1-sun excitation based on pulse-excitation measurements. This would help directly bridge the fundamental understanding of material property and actual device performance!

Our recent paper was featured in several Japanese media! Thank you!

Our paper (done at Kyoto University) was published in Science Advances! We report the observation of correlated luminescence and ferroelectric properties in a metal-free ferroelectric halide perovskite!

I gave a talk at the MRSEC symposium.

Collarborative work on world-record lead-tin perovskite solar cells was published in Energy Environ. Sci.! We discuss the carrier dynamics in the high-quality perovskite thin films.

I joined an online class at a middle school in Fukuoka, where we discussed my career path as a scientific researcher. I had big fun talking with ambitious students.

Collarborative work on highly efficient lead-tin mixed perovskite solar cells was published in Chem. Sci.!

Our spotlight paper, which discusses fundamental optical properties and introduces novel strategies to achieve efficient lead-free tin perovskite solar cells, was published in ACS Appl. Electron. Mater. (written with Prof. Wakamiya group)!

Our perspective on phonon, thermal, and thermo-optical properties of halide perovskites was published in Phys. Chem. Chem. Phys.! The paper will be free to access until the end of February 2021 as it was selected as 2020 HOT PCCP article.

Attended the JSAP Fall meeting @ online.

Our paper reporting on the origin of unusual temperature dependence of refractive index in halide perovskite was published in Physical Review Materials (open access)!

Collaborative work on lead-free Sn perovskites with very high quality was published in Nature Communications!

Our review paper on optical response of lead halide perovskite was published in Semiconductor Science and Technology!

I received a doctoral degree from Kyoto University.

Collaborative work on new lead-free metal halide materials was published in APL Materials! See also Scilight.

I had a presentation at JPS meeting @GifuUniv (awarded the student presentation award).

Our review article on the photophysics of lead-free tin perovskites is now out in APL Materials (open access)!

We were awarded the JSAP Best Review Paper Award.

Our paper reporting negative thermo-optic coefficients in lead halide perovskite was published in Science Advances!
We demonstrated new optical applications using the discovered unique thermo-optic properties. Check this OA paper!

Attended JSAP Spring Meeting @ Tokyo Tech

I had an invited talk at 14th IUPAC International Conference (NMS-XIV)@Guangzhou, China.

Collaborative work on tin halide perovskite solar cells was published in Angewandte Chemie Int. Ed.!

Our review paper on perovskite semiconductors and solar cells was published in Japanese Journal of Applied Physics!

Our paper on band-edge optical properties of lead-free tin perovskites was published in Physical Review Materials!

I had a commemorative lecture at JSAP Spring meeting, Waseda Univ.

I had an invited lecture at iCeMS-VISTEC Joint Symposium@Thailand.

I was awarded the JSAP Young Scientist Presentation Award.

Collaborative work on solvent-coordinated tin-halide complexes was published in ACS Omega!

Attended and had a presentation in 13th IUPAC International Conference (NMS-XIII), Nanjing.

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