Dr. Takashi Fujihara Profile

Dr. Takashi Fujihara

Research Associate at ISIT

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Publications (2)

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Proceedings Article | 19 September 2017 Presentation

Introduction of benzoquinone additive for efficient and stable planar perovskite solar cells (Conference Presentation)

Chuanjiang Qin, Toshinori Matsushima, Takashi Fujihara, Chihaya Adachi

Proceedings Volume 10363, 103631F (2017) https://doi.org/10.1117/12.2271593

KEYWORDS: Solar cells, Materials processing, Lead, Crystals, Photovoltaics, Reliability, Fabrication, Printing

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Organic-inorganic perovskites have emerged as an interesting class of materials that have excellent photovoltaic properties for application to solar cells. The power conversion efficiency of perovskite solar cells over 20% has already been realized through systematic optimization of materials and fabrication processes. However, the long-term stability of perovskite solar cells still need to be improved for practical applications. In this study, we introduced a multifunctional benzoquinone (BQ) additive into a precursor solution containing methylammonium iodide (MAI) and lead iodide (PbI2) used for spin-coating of perovskite films. Resulting spin-coated perovskite films containing BQ had the improved perovskite morphology and crystal quality because of intermolecular interaction between MAI and BQ slowing the rate of perovskite crystal formation. Therefore, we obtained the greatly enhanced power conversion efficiency from 10.7% to 15.6%. The reduced charge recombination loss by electron transfer from perovskite to BQ is another source of the improved efficiency. In addition to the efficiency enhancement, the BQ addition led to the extended lifetime about twenty-six times. The lifetime, at which efficiency reduces to 80% of the initial under the one-sun condition (100 mW/cm2 and AM1.5G), reached about 4000 h, one of the longest lifetimes ever reported in perovskite solar cells. The extended lifetime can be explained by the reduced formation of carrier traps originating from metallic lead during solar irradiation as the results of thermally stimulate current measurements. We believe that the present findings offer insight to help obtain efficient, stable organic-inorganic perovskite solar cells for future applications.

Proceedings Article | 2 November 2016 Presentation

High-hole-mobility organic-inorganic perovskite field-effect transistors (Conference Presentation)

Toshinori Matsushima, Sun Bin Hwang, Atula Sandanayaka, Chuanjiang Qin, Takashi Fujihara, Masayuki Yahiro, Chihaya Adachi

Proceedings Volume 9943, 994305 (2016) https://doi.org/10.1117/12.2236265

KEYWORDS: Perovskite, Transistors, Semiconductors, Organic semiconductors, Semiconductor materials, Tin, Silica, Self-assembled monolayers, Coating, Electrodes

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We have recently focused our attention on the application of perovskite materials to a semiconducting layer in field-effect transistors. Because perovskite materials are expected to promise the processability and flexibility inherent to organic semiconductors as well as the superior carrier transport inherent to inorganic semiconductors, we believe that organic semiconductor-like cost-effective, flexible transistors with inorganic semiconductor-like high carrier mobility can be realized using perovskite semiconductors in future. In this study, we have prepared the tin iodide-based perovskite as a semiconducting layer on silicon dioxide layers treated with a self-assembled monolayer containing ammonium iodide terminal groups by spin coating and, then, source-drain electrodes on the perovskite layer by vacuum deposition for the fabrication of a top-contact perovskite transistor. Because of a well-developed perovskite layer formed on the treated substrate and reduced contact resistance resulting from the top-contact structure, we have obtained a new record hole mobility of up to 12 cm2 V–1 s–1 in our perovskite transistors, which is about five times higher than a previous record hole mobility and is considered to be a very good value when compared with widely investigated organic transistors. Along with the high hole mobility, we have demonstrated that this surface treatment leads to smaller hysteresis in output and transfer characteristics and better stress stability under constant gate voltage application. These findings open the way for huge advances in solution-processable high-mobility transistors.

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