Research.研究

非対称な不純物効果：有機太陽電池、フラーレン混合物の新発見 Asymmetric Impurity Effects: New Findings in Organic Solar Cell – Fullerene Mixtures.

有機太陽電池研究のブレークスルー：非対称な不純物効果を発見 Breakthrough in Organic Photovoltaic Research: Asymmetrical Impurity Effects Discovered

有機太陽電池の分野で嘉治研究室の研究者たちが重要な発見をしました。C70:C60フラーレン混合物における予想外の非対称な不純物効果が明らかになりました。この研究は2024年5月号のOrganic Electronics誌に掲載され、有機半導体デバイスで人気の受容体材料の挙動に新たな光を当てています。Researchers (from Kaji Lab) have made a significant discovery in the field of organic photovoltaics, revealing an unexpected asymmetrical impurity effect in C70:C60 fullerene mixtures. The study, published in the May 2024 issue of Organic Electronics, sheds new light on the behavior of these popular acceptor materials in organic semiconductor devices.Key findings include:

主な発見には以下が含まれます：Key findings include:

  1. C70中のC60、C78、C84不純物が電子輸送中のキャリア再結合を引き起こす。C60, C78, and C84 impurities in C70 caused carrier recombination during electron transport.
  2. C60中のC70不純物の影響は、C70中のC60不純物の影響よりも大幅に小さい。The effect of C70 impurities in C60 was significantly smaller than C60 impurities in C70.
  3. 高次フラーレン不純物がC70に与える影響は、C60に与える影響よりも明らかに大きい。Higher fullerene impurities had a more pronounced effect on C70 compared to C60.

研究チームは、ドナー材料として亜鉛フタロシアニン（ZnPc）を、アクセプター材料として様々な純度のC70を使用し、この非対称効果を実証しました。彼らは、C70不純物の浅いトラッピングがC60のキャリア輸送を大きく妨げないのに対し、C60不純物はC70のキャリア輸送を大きく阻害すると示唆しています。この研究では、昇華を利用したC70の効果的な精製方法も紹介されており、有機太陽電池やペロブスカイト太陽電池の効率向上に重要な意味を持つ可能性があります。これらの発見は、有機エレクトロニクスにおけるフラーレン混合物の理解を深め、より効率的で費用対効果の高い太陽エネルギー技術の開発につながる可能性があります。The research team used zinc phthalocyanine (ZnPc) as a donor material and C70 with various purities as an acceptor to demonstrate this asymmetrical effect. They suggest that the shallow trapping of C70 impurities doesn’t significantly hinder photocarrier transport in C60, while C60 impurities greatly inhibit transport in C70. This study also introduces an effective purification method for C70 using sublimation, which could have important implications for improving the efficiency of organic photovoltaic cells and perovskite solar cells. These findings contribute to a deeper understanding of fullerene mixtures in organic electronics and may lead to more efficient and cost-effective solar energy technologies.

Schematic of fullerene sublimation for C70 purification. (A) First sublimation of the fullerene mixture. (B) Sublimation rate of C60 and C70 in a tube furnace from a fullerene mixture source depending on the amount of source. (C) Second sublimation from the C70 crystal (67% purity) obtained by the first sublimation. C70精製のためのフラーレン昇華の模式図。(A）フラーレン混合物の最初の昇華。(B）フラーレン混合ソースからの管状炉内でのC60とC70の昇華速度（ソースの量に依存）。(C）1回目の昇華で得られたC70結晶（純度67％）からの2回目の昇華。

https://doi.org/10.1016/j.orgel.2024.107021

Organic Electronics

Volume 128, May 2024, 107021

Organic Electronics

Asymmetrical impurity effect of C70:C60 mixture in thick small molecule organic photovoltaic cells

Highlights

  • •A strange asymmetrical impurity effect of the C60:C70 mixture was demonstrated.
  • •C60, C78, and C84 impurities in C70 caused carrier recombination during electron transport.
  • •The effect of the C70 impurity in C60 was much smaller than the effect of C60 impurity in C70.
  • •The impurity effect of higher fullerenes on C70 was clearly larger than that of C60.
  • •An effective purification method for C70 using sublimation purification is reported.

Abstract

Fullerenes, especially C70 and C60, and their derivatives are popular acceptor materials for many organic semiconductor devices, including organic photovoltaic cells. One of the main impurities in C70 is C60, and intentional mixture of C60 and C70, or their derivatives, which have been utilized for maximizing the performance of organic photovoltaic cells or perovskite solar cells. However, the influence of impurities in C70 on the device characteristics has not been fully clarified when incorporating C70 into organic devices. To further clarify the relationship between the fullerene mixture and impurities, the effect of impurities in fullerenes on thick photovoltaic cells was evaluated, and a strange asymmetrical impurity effect of the C60:C70 mixture was demonstrated by using C70 with various purities as an acceptor material and zinc phthalocyanine (ZnPc) as a donor material. It was found that C60, C78, and C84 impurities in C70 caused carrier recombination during electron transport, but the same effect of the C70 impurity in C60 was much smaller. Additionally, the impurity effect of higher fullerenes on C70 was clearly larger than that of C60. The effect of higher fullerene impurities can be explained by electron trapping due to their deep lowest unoccupied molecular orbital (LUMO) levels. For the small difference of LUMO energy between C70 and C60, however, it is suggested that the shallow trapping of C70 impurities does not largely inhibit the transport of photocarriers by C60, while the low energy barrier of C60 impurities largely inhibits the transport of photocarriers by C70. For clear comparison, the photoelectrical conversion layers were crystallized using co-evaporant induced crystallization. An effective purification method for C70 using sublimation purification, which depends on the C70 concentration in the sublimation source, is also reported.