Research Activities

Using time-resolved spectroscopic techniques with ultra-short pulse lasers, we elucidate the dynamics of excitons and charges generated in organic materials. Furthermore, we develop organic optoelectronic devices based on photophysical phenomena occurring at the bulk and interface of organic materials.

Literature

Y. Tamai, Y. Murata, S. Natsuda, Y. Sakamoto, “How to Interpret Transient Absorption Data?: An Overview of Case Studies for Application to Organic Solar Cells”, Adv. Energy Mater., 14, 2301890 (2024)
K. Kohzuki, R. Shirouchi, S. Natsuda, T. Saito, Y. Sakamoto, Y. Tamai, “Charge Separation from Triplet Excited States in Nonfullerene Acceptor-Based Organic Solar Cells”, Sol. RRL, 7, 2300359 (2023)
Y. Tamai, R. Shirouchi, T. Saito, K. Kohzuki, S. Natsuda, “Role of the Energy Offset in the Charge Photogeneration and Voltage Loss of Nonfullerene Acceptor-Based Organic Solar Cells”, J. Mater. Chem. A, 11, 17581 (2023).
T. Saito, S. Natsuda, R. Shirouchi, K. Imakita, K. Kohzuki, Y. Tamai, “Intrinsic Advantage of Fused-Ring Nonfullerene Acceptor-Based Organic Solar Cells to Reduce Voltage Loss”, Phys. Status Solidi A, 220, 2300121 (2023)
Y. Tamai, “What’s Next for Organic Solar Cells? The Frontiers and Challenges”, Adv. Energy Sustainability Res., 4, 2200149 (2023).
Y. Sakamoto, Y. Tamai, “Unlocking the Full Potential of Polymer-Based Solid-State Photon Upconversion”, ECS J. Solid State Sci. Technol., 11, 121005 (2022).
Y. Tamai, “Charge Generation in Organic Solar Cells: Journey toward 20% Power Conversion Efficiency”, Aggregate, 3, e280 (2022).
Y. Sakamoto, S. Izawa, H. Ohkita, M. Hiramoto, Y. Tamai, “Triplet Sensitization via Charge Recombination at Organic Heterojunction for Efficient Near-Infrared to Visible Solid-State Photon Upconversion”, Commun. Mater., 3, 76 (2022).
S. Natsuda, T. Saito, R. Shirouchi, K. Imakita, Y. Tamai, “Delocalization Suppresses Nonradiative Charge Recombination in Polymer Solar Cells”, Polym. J., 54, 1345–1353 (2022).
Y. Murata, Y. Tamai, “Intrachain Exciton Motion Can Compete with Interchain Hopping in Conjugated Polymer Films with a Strong J-Aggregate Property”, J. Phys. Chem. Lett., 13, 2078–2083 (2022).
S. Natsuda, T. Saito, R. Shirouchi, Y. Sakamoto, T. Takeyama, Y. Tamai, H. Ohkita, “Cascaded Energy Landscape as a Key Driver for Slow yet Efficient Charge Separation with Small Energy Offset in Organic Solar Cells”, Energy Environ. Sci., 15, 1545–1555 (2022).
M. Nakamura, M. Gon, S. Natsuda, Y. Tamai, H. Ohkita, K. Tanaka, Y. Chujo, “Development of NIR Emissive Fully-Fused Bisboron Complexes with π-conjugated Systems Including Multiple Azo Groups”, Dalton Trans., 51, 74–84 (2022).
S. Natsuda, Y. Sakamoto, T. Takeyama, R. Shirouchi, T. Saito, Y. Tamai, H. Ohkita, “Singlet and Triplet Excited-State Dynamics of a Nonfullerene Electron Acceptor Y6”, J. Phys. Chem. C, 125, 20806–20813 (2021).
T. Umeyama, T. Wada, K. Igarashi, K. Kato, A. Yamakata, T. Takeyama, Y. Sakamoto, Y. Tamai, H. Ohkita, K. Ishida, T. Koganezawa, S. Ohtani, K. Tanaka, H. Imahori, “Effect of Terminal-Group Halogenation of Naphthalene-Based Nonfullerene Acceptors on Their Film Structure and Photophysical and Photovoltaic Properties”, ACS Appl. Energy Mater., 4, 14022–14033 (2021).
T. Fukuhara, K. Yamazaki, T. Hidani, M. Saito, Y. Tamai, I. Osaka, H. Ohkita, “Molecular Understanding of How the Interfacial Structure Impacts the Open-Circuit Voltage of Highly Crystalline Polymer Solar Cells”, ACS Appl. Mater. Interfaces, 13, 34357–34366 (2021).
T. Umeyama, K. Igarashi, Y. Tamai, T. Wada, T. Takeyama, D. Sasada, K. Ishida, T. Koganezawa, S. Ohtani, K. Tanaka, H. Ohkita, H. Imahori, “Prolongation of the Singlet Exciton Lifetime of Nonfullerene Acceptor Films by the Replacement of the Central Benzene Core with Naphthalene”, Sustain. Energy Fuels, 5, 2028–2035 (2021).
M. Saito, T. Fukuhara, S. Kamimura, H. Ichikawa, H. Yoshida, T. Koganezawa, Y. Ie, Y. Tamai, H. D. Kim, H. Ohkita, I. Osaka, “Impact of Noncovalent Sulfur–Fluorine Interaction Position on Properties, Structures, and Photovoltaic Performance in Naphthobisthiadiazole‐Based Semiconducting Polymers”, Adv. Energy Mater., 10, 1903278 (2020).
M. Saito, Y. Tamai, H. Ichikawa, H. Yoshida, D. Yokoyama, H. Ohkita, I. Osaka, “Significantly Sensitized Ternary Blend Polymer Solar Cells with a Very Small Content of the Narrow-Band Gap Third Component That Utilizes Optical Interference”, Macromolecules, 53, 10623–10635 (2020).
Y. Sakamoto, Y. Tamai, H. Ohkita, “Sensitizer–Host–Annihilator Ternary-Cascaded Triplet Energy Landscape for Efficient Photon Upconversion in the Solid State”, J. Chem. Phys., 153, 161102 (2020).
T. Saito, S. Natsuda, K. Imakita, Y. Tamai, H. Ohkita, “Role of Energy Offset in Nonradiative Voltage Loss in Organic Solar Cells”, Sol. RRL, 4, 2000255 (2020).
Y. Murata, T. Takeyama, Y. Sakamoto, K. Yamaguchi, Y. Tamai, H. Ohkita, “Two-Dimensional Exciton Diffusion in an HJ-Aggregate of Naphthobisoxadiazole-Based Copolymer Films”, J. Phys. Chem. C, 124, 13063–13070 (2020).
T. Umeyama, K. Igarashi, D. Sasada, Y. Tamai, K. Ishida, T. Koganezawa, S. Ohtani, K. Tanaka, H. Ohkita, H. Imahori, “Efficient Light-Harvesting, Energy Migration, and Charge Transfer by Nanographene-Based Nonfullerene Small-Molecule Acceptors Exhibiting Unusually Long Excited-State Lifetime in the Film State”, Chem. Sci., 11, 3250–3257 (2020).
T. Fukuhara, Y. Tamai, H. Ohkita, “Nongeminate Charge Recombination in Organic Photovoltaics”, Sustain. Energy Fuels, 4, 4321–4351 (2020).
Y. Tamai, “Delocalization Boosts Charge Separation in Organic Solar Cells”, Polym. J., 52, 691–700 (2020).
K. Midori, T. Fukuhara, Y. Tamai, H. D. Kim, H. Ohkita, “Enhanced Hole Transport in Ternary Blend Polymer Solar Cells”, ChemPhysChem, 20, 2683–2688 (2019).
T. Fukuhara, Y. Tamai, I. Osaka, H. Ohkita, “Bimolecular Recombination and Fill Factor in Crystalline Polymer Solar Cells”, Jpn. J. Appl. Phys., 57, 08RE01 (2018).
Y. Tamai, Y. Fan, V. O. Kim, K. Ziabrev, A. Rao, S. Barlow, S. R. Marder, R. H. Friend, S. M. Menke, “Ultrafast Long-Range Charge Separation in Nonfullerene Organic Solar Cells”, ACS Nano, 11, 12473–12481 (2017).
H. Ohkita, Y. Tamai, H. Benten, S. Ito, “Transient Absorption Spectroscopy for Polymer Solar Cells”, IEEE J. Sel. Top. Quantum Electron., 22, 100–111 (2016).
Y. Tamai, H. Ohkita, M. Namatame, K. Marumoto, S. Shimomura, T. Yamanari, S. Ito, “Light-Induced Degradation Mechanism in Poly(3-hexylthiophene)/Fullerene Blend Solar Cells”, Adv. Energy Mater., 6, 1600171 (2016).
T. Fukuhara, M. Osaka, Y. Tamai, H. Ohkita, H. Benten, S. Ito, “Reduced Bimolecular Recombination in Polymer Solar Cells”, J. Photopolym. Sci. Technol., 29, 575–580 (2016).
H. Xu, H. Ohkita, Y. Tamai, H. Benten, S. Ito, “Interface Engineering for Ternary Blend Polymer Solar Cells with a Heterostructured Near-IR Dye”, Adv. Mater., 27, 5868–5874 (2015).
Y. Kasai, Y. Tamai, H. Ohkita, H. Benten, S. Ito, “Ultrafast Singlet Fission in a Push-Pull Low-Bandgap Polymer Film”, J. Am. Chem. Soc., 137, 15980–15983 (2015).
K. Kawashima, Y. Tamai, H. Ohkita, I. Osaka, K. Takimiya, “High-Efficiency Polymer Solar Cells with Small Photon Energy Loss”, Nat. Commun., 6, 10085 (2015).
Y. Tamai, H. Ohkita, H. Benten, S. Ito, “Exciton Diffusion in Conjugated Polymers: From Fundamental Understanding to Improvement in Photovoltaic Conversion Efficiency”, J. Phys. Chem. Lett., 6, 3417-3428 (2015).
Y. Tamai, K. Tsuda, H. Ohkita, H. Benten, S. Ito, “Charge-Carrier Generation in Organic Solar Cells using Crystalline Donor Polymers”, Phys. Chem. Chem. Phys., 16, 20338–20346 (2014).
Y. Wang, B. Zheng, Y. Tamai, H. Ohkita, H. Benten, S. Ito, “Dye Sensitization in the Visible Region for Low-Bandgap Polymer Solar Cells”, J. Electrochem. Soc., 161, D3093–D3096 (2014).
Y. Tamai, H. Ohkita, H. Benten, S. Ito, “Triplet Exciton Dynamics in Fluorene−Amine Copolymer Films”, Chem. Mater., 26, 2733–2742 (2014).
Y. Tamai, Y. Matsuura, H. Ohkita, H. Benten, S. Ito, “One-Dimensional Singlet Exciton Diffusion in Poly(3-hexylthiophene) Crystalline Domains”, J. Phys. Chem. Lett., 5, 399–403 (2014).
Y. Tamai, H. Ohkita, J. Shimada, H. Benten, S. Ito, S. Yamanaka, K. Hisada, K. Tani, K. Kubono, T. Shinmyozu, “Dynamical Excimer Formation in Rigid Carbazolophane via Charge Transfer State”, J. Phys. Chem. A, 117, 7776–7785 (2013).
Y. Tamai, H. Ohkita, H. Benten, S. Ito, “Singlet Fission in Poly(9,9’-di-n-octylfluorene) Films”, J. Phys. Chem. C, 20, 10277–10284 (2013).
H. Aoki, T. Takahashi, Y. Tamai, R. Sekine, S. Aoki, K. Tani, S. Ito, “Poly(methacrylate)s Labeled by Perylene Diimide: Synthesis and Applications in Single Chain Detection Studies”, Polym. J., 41, 778–783 (2009).
Y. Tamai, R. Sekine, H. Aoki, S. Ito, “Conformation of Single Homopolymer Chain in Microphase-Separated Block Copolymer Monolayer Studied by Scanning Near-Field Optical Microscopy”, Macromolecules, 42, 4224–4229 (2009).

Other Activities

The Japanese Photochemistry Association, Japan Society of Applied Physics, The Society of Polymer Science, The Chemical Society of Japan

Future Plan

We conduct research on the photophysics and photovoltaic conversion devices of organic semiconductors utilizing various spectroscopic techniques.

Messages to Students

Organic semiconductors are expected to be the next-generation semiconductor materials due to their potential advantages compared to inorganic semiconductors, such as flexibility and color tunability. Let's contribute to solving energy issues through the development of organic optoelectronic devices.

URL

http://www.organicel.k.u-tokyo.ac.jp/