Sunday, 15 Sep 2019

Riken reaches 9% efficiency with polymer OPV and boosts thermal resistance

The research team have built on a previously developed organic semiconductor polymer PTzBT - originally announced in 2012

2 Oct 2015 | Editor

Riken has announced they have developed a novel p-type polymer material - PTzNTz (thiophene and thiazolothiazole) with the aim to improving the power efficiency of organic photovoltaics (OPV). The work has been published in Nature's Scientific Reports.

The research team have built on a previously developed organic semiconductor polymer PTzBT - originally announced in 2012. More specifically the researchers wanted to improved power conversion efficiency and heat resistance. The researchers achieved improved the power conversion efficiency from 7% to 9% - (open-circuit voltage: 0.84V, short-circuit current: 16.0mA, fill factor: 0.67).

Devices made from the PTzBT polymer was subjected to accelerated testing at 85oC for 500 hours its efficiency was reduced to about 40% of its initial value. In contrast when PTzNTz was subjected to the same operating conditions its power conversion efficiency fell only by a small amount to 90% of its initial value. The researchers also extrapolated the results and found that the power conversion efficiency would still be about 90% of initial value even after more than 1,000 hours.

The accelerated test to evaluate the durability of these polymers while impressive still has more work to be done. At present the exact reason for this improvement is still not clear. More research is to be undertaken. The researchers believe this demonstrates that organic semiconductor polymers are moving closer to being viable for commercial use.

Riken - Organic PV materials<

Figure: Riken - Organic PV materials

Highly Efficient and Stable Solar Cells Based on Thiazolothiazole and Naphthobisthiadiazole Copolymers

Masahiko Saito | Itaru Osaka | Yasuhito Suzuki | Kazuo Takimiya | Takashi Okabe | Satoru Ikeda | Tsuyoshi Asano

Scientific Reports 5, Article number: 14202 (2015) | doi:10.1038/srep14202

Received: 22 June 2015 | Accepted: 21 August 2015 | Published online: 23 September 2015


A critical issue in polymer-based solar cells (PSCs) is to improve the power conversion efficiency (PCE) as well as the stability. Here, we describe the development of new semiconducting polymers consisting of thiophene, thiazolothiazole and naphthobisthiadiazole in the polymer backbone. The polymers had good solubility and thus solution-processability, appropriate electronic structure with narrow band gaps of ~1.57 eV and low-lying HOMO energy levels of ~−5.40 eV, and highly ordered structure with the favorable face-on backbone orientation. Solar cells based on the polymers and PC71BM exhibited quite high PCEs of up to 9%. More interestingly, the cells also demonstrated excellent stability as they showed negligible degradation of PCE when stored at 85˚C for 500 hours in the dark under nitrogen atmosphere. These results indicate that the newly developed polymers are promising materials for PSCs in the practical use.

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