Aiming at the problems of few types of conjugated materials, difficult control of condensed state structure, and low energy conversion efficiency in single-component organic solar cells, a joint research group at home and abroad has recently made new breakthroughs. They synthesized a new type of double-cable conjugated polymer and used it as a light-absorbing layer in a single-component organic solar cell to obtain an energy conversion efficiency of 6.3%, which is currently the highest single-component organic solar cell efficiency. Related papers were published in "Joule" recently.

"The polymer contains the donor main chain and the acceptor side chain. During the film formation process, the donor and acceptor restrict each other, making it difficult to form ordered nanostructures. We found that temperature gives these polymers the opportunity for secondary crystallization As the temperature increases, the accumulation of the donor main chain and the acceptor side chains in the polymer film is gradually ordered, which greatly improves the charge transfer efficiency and reduces the probability of charge recombination. Li Weiwei, a professor at the Institute / Beijing University of Chemical Technology, told the China Science Journal.

It is reported that compared with the traditional multi-component bulk heterojunction battery, the single-component organic solar cell contains only one component in the active layer, thereby greatly improving device stability and simplifying the device manufacturing process. Moreover, the single-component organic solar cell based on the double-cable conjugated polymer has limited activity due to the "binding" of the donor and acceptor through chemical bonds, and its morphological stability has been proven to be superior to the corresponding bulk heterojunction cell . At the same time, in the double-cable type conjugated polymer, the interface between the donor and acceptor is evenly distributed on the molecular scale, which facilitates the diffusion of excitons to the interface within a limited lifetime. Therefore, single-component solar cells based on double-cable conjugated polymers have large-scale industrial application potential.

Although this type of battery has a decades of research history, its efficiency is still far lower than that of bulk heterojunction batteries. The main reason is that the synthesis of single-component conjugated materials is complicated, and it is difficult to control the phase separation of the intramolecular donor / acceptor. Based on this, Li Weiwei's research group regained the historical problem—single component organic solar cell research.

Previously, in response to the complex problem of the synthesis of double-cable conjugated polymers, the research group proposed a design idea of ​​"functionalization of side chains first, followed by polymerization", and successfully prepared a series of clearly structured double-cable conjugated polymers. The mechanism of the influence of the molecular structure of the conjugated main chain, acceptor side chain and connecting unit on the polymer condensed state structure was explored, which improved the efficiency of single-component organic solar cells from 0.51% to 4.34%.

This time, Li Weiwei's research team, together with researchers from the University of Nuremberg and the Hong Kong University of Science and Technology, introduced benzodithiophene dione into the conjugated main chain to synthesize the fourth series of double-cable conjugated polymers. The phase separation morphology in is sensitive to temperature. As the annealing temperature increases, the accumulation of the donor main chain and the acceptor side chain of the polymer gradually becomes ordered, and the related solar cell obtains a photoelectric conversion efficiency of 6.3%.

The researchers also systematically studied many of the mechanical problems of the battery in operation, and found that it could still maintain an initial efficiency of 93% after 300 hours of continuous sunlight exposure.

The researchers said that this series of studies proves that with the development of new materials and the continuous advancement of photoelectric conversion mechanism research, single-component organic solar cells "old pot new wine" have great research value and application potential.

It is reported that the first author of the paper is Feng Guitao, a PhD student in the research group, and the corresponding authors are Li Weiwei and Li Cheng, associate researcher of the Institute of Chemistry, Chinese Academy of Sciences. (Reporter Tang Feng)

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