Organic solar cells, which are both efficient and flexible, are expected to be easy to prepare

Recently, the organic optoelectronic materials and device team of Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences proposed a strategy of incorporating flexible oligomer receptors as the third component into the active layer of organic solar cells, which can simultaneously improve the photoelectric conversion efficiency and mechanical properties of organic solar cells, providing a simple method for the preparation of high-efficiency flexible organic solar cells.

With the growth of the wearable electronic device market, users have increasingly stringent requirements for wearable power generation devices. Organic solar cells are ideal solutions for flexible power sources due to their light weight, strong design and easy processing. However, compared with rigid organic solar cells with photoelectric conversion efficiency exceeding 19%, flexible organic solar cells still have shortcomings in photoelectric conversion efficiency and mechanical properties. Therefore, the development of flexible organic solar cells with high photoelectric conversion efficiency and high mechanical stability is still extremely challenging.

The researchers first synthesized a series of oligomer receptor materials (DOY-C2, DOY-C4, and TOY-C4) with different bridging units and degrees of polymerization by using different flexible bridging segments. Due to the different degree of polymerization and bridging unit flexibility, these oligomer receptors also exhibit different mechanical properties and packing behavior. At the same time, compared with the traditional small molecule acceptor material N3, the flexible oligomeric receptor exhibits significantly better mechanical properties.

In order to explore the effect of oligomeric acceptors as the third component on the efficiency of organic solar cells, the researchers prepared corresponding rigid battery devices. Through characterization tests of various parameters of the battery, the researchers found that the incorporation of oligomer receptors mainly increases the open-circuit voltage of the battery by reducing the non-radiative energy loss in organic solar cells. Among them, the device based on D18:N3:DOY-C4 shows a rigid photoelectric conversion efficiency of 19.01% and a flexible photoelectric conversion efficiency of 17.91%, which is also one of the highest efficiency of flexible organic solar cells currently reported.

Subsequently, the researchers performed tensile tests on the active layer material. Compared with the 7.8% elongation at break of the D18:N3 hybrid film, the hybrid film doped with the 15% oligomer DOY-C4 showed a fracture elongation of nearly 12%, an increase of more than 50% year-on-year. Through the analysis of the topography of different films after stretching, the authors believe that flexible oligomeric acceptors can form entangle-like behaviors with polymer donors, which leads to a significant increase in the mechanical properties of the films.

The results were recently published in Advanced Materials, with Ye Qinrui and Chen Zhenyu, doctoral students of Ningbo Institute of Materials as co-first authors, and Song Wei, a distinguished young researcher of the Institute, and Ge Ziyi, a researcher, as the corresponding authors.

Fracture after stretching and relaxation after stretching of different films. Photo courtesy of Ningbo Materials

(Source: Zhang Nan, China Science News)

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