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Kyoto University develops new material that will push perovskite solar cells towards 20% efficiency

Perovskite solar cells manufactured using solution processing are expected to offer solar power at a dramatically lower cost compared to alternative solar cells

11 Dec 2015 | Editor

Kyoto University has published a paper on 11, 2015, that the researchers have developed a material capable of improving the conversion efficiency of perovskite solar cell to 16.5%.

A research group led by Atsushi Wakamiya (associate professor at the Institute for Chemical Research, Kyoto University) have developed an organic semiconductor material having its own "cushion-like structure" in a joint research with Akinori Saeki (associate professor at Osaka University) and Lawrence Scott (professor emeritus at Boston College).

By using the material for the buffer layer of the p-type semiconductor, the conversion efficiency of perovskite solar cell was improved.

Kyoto University considers that the latest result will be a guiding principle for the molecular design of organic semiconductor materials capable of improving the efficiency of perovskite solar cell.

The development of low-cost materials having excellent characteristics will continue to make good progress, accelerating the research toward the commercialisation of perovskite solar cell.

The power conversion efficiency of perovskite solar cells has been improved mainly by improvements to the method to make the perovskite layer - which is a light-absorbing material.

However, for the buffer layer that extracts electric charges generated by light from the perovskite layer there are few materials having excellent characteristics. So "Spiro-OMeTAD" - an organic semiconductor material whose manufacturing cost is high - has been used.

Therefore, for the commercialisation, there was a need to develop an organic semiconductor material that has a excellent characteristics coupled with a lower manufacturing cost.

Kyoto University et al - Improved perovskite soalr cell material

Figure: Kyoto University et al - Improved perovskite soalr cell material

During the research program a "solution coatable" organic semiconductor material - "HND-Azulene" - was developed based on a molecular design that expands the structure into a two-dimensional sheet having a "cushion-like" structure. By using the material for the p-type buffer layer, the conversion efficiency was improved by 20%, compared with the case in which a more conventional material is used, realising an efficiency of 16.5%.

Hole-Transporting Materials with a Two-Dimensionally Expanded π-System around an Azulene Core for Efficient Perovskite Solar Cells

Hidetaka Nishimura† | Naoki Ishida‡ | Ai Shimazaki†| Atsushi Wakamiya*†§ | Akinori Saeki*‡ | Lawrence T. Scott*∥ | Yasujiro Murata*†

† Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan

‡ Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan

§ Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan

∥ Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467-3860, United States

J. Am. Chem. Soc. | DOI: 10.1021/jacs.5b11008 | Publication Date (Web): December 10, 2015


Two-dimensionally expanded π-systems, consisting of partially oxygen-bridged triarylamine skeletons that are connected to an azulene (1–3) or biphenyl core (4), were synthesized and characterized. When tetra-substituted azulene 1 was used as a hole-transporting material (HTM) in perovskite solar cells, the observed performance (power conversion efficiency = 16.5%) was found to be superior to that of the current HTM standard Spiro-OMeTAD. A comparison of the hole mobility, the ability to control the HOMO and LUMO levels, and the hole-collection efficiency at the perovskite/HTM interface in 1 with reference compounds (2–4 and Spiro-OMeTAD) led to the elucidation of key factors required for HTMs to act efficiently in perovskite solar cells.

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