News Resource & Photographer: School of Chemistry and Chemical Engineering

Editor: News Agency of BIT

Translator: Huang Yuwei, News Agency of BIT

Beijing Institute of Technology (BIT), August 26th, 2021: Recently, Jiang Mengyun, a graduate student from School of Chemistry and Chemical Engineering of BIT, has published a research paper titled “Two-Pronged Effect of Warm Solution and Solvent-Vapor Annealing for Efficient and Stable All-Small-Molecule Organic Solar Cells” in international top journal ACS Energy Letters as the first author. BIT is the first correspondent. Special researcher An Qiaoshi, professor Wang Jinliang of BIT and professor Zhang Fujun of Beijing Jiaotong University are co-corresponding authors. The research is funded by National Natural Science Foundation of China, Natural Science Foundation of Beijing, Beijing Institute of Technology Research Fund Program for Young Scholars and other projects, and supported by Analysis & Testing Center of BIT.

Organic solar cells (OSCs) has a series of unique advantages including abundant raw materials, light weight, flexibility, translucency, rich colors, large-area preparation and so on, which is a potential green photoelectric conversion technology. It is in line with the requirements of Chinese sustainable development and has become one of the most dynamic research frontiers in the field of new energy. Small molecular materials have the advantages of clear molecular structure, high repeatability, easy preparation and purification. Based on the small molecule donor-acceptor materials, OSCs shows great commercial potential. However, because the morphology of small molecule active layer is sensitive and difficult to control, its efficiency is far behind other types of OSCs.

Effects of different treatment processes on surface morphology and bulk morphology of active layer

In this research, the researchers use two strategies, warm solution (WS) and solvent-vapor annealing (SVA), to regulate the active layers morphology of small molecule. WS can not only improve the solubility of donor-acceptor materials, B1 and BTP-eC9, but also accelerate solvent volatilization in the film-forming process, reduce the film-forming time, make the molecular distribution more uniform in the active layer, and form a smooth non-porous mixed thin film. SVA can regulate the molecular dynamics after filming formation and prolong the time of molecular self-assembly. The phase separation and molecular arrangement in the active layer can be optimized by controlling the SVA time. Through the synergy of WS + SVA, the morphology of the active layer has been greatly improved. It improves the photon acquisition, exciton dissociation, carrier transmission and collection of the device, so that it obtains an efficiency of 15.68%, which is the highest values of binary all-small-molecule OSCs at that time.

Paper Link: https://pubs.acs.org/doi/10.1021/acsenergylett.1c01289