Biography:

Dr. Fujun Zhang is a professor in the Faculty of Science, Beijing Jiaotong University. He is one of the Outstanding Hundred Talents in China. He holds the National Natural Science Foundation of China, Beijing Natural Science Foundation, Special project of basic Scientific Research Funds for universities of Ministry of Education in China. He has published more than 120 SCI-indexed papers, including nearly 70 papers as the first author or corresponding author, which have been cited by SCI more than 1800 times and 7 papers with an impact factor greater than 10. In 2016, he was invited to join the editorial board of Scientific Report journal.

Speech title: Recent development of ternary organic solar cells

Abstract: Organic photovoltaics are widely concerned because of their advantages of low cost, light weight, flexibility and large area preparation. In recent years, thanks to the emergence of various non-fullerene materials, organic photovoltaics have been rapidly developed and have reached the "dawn" of commercialization. In addition to material innovation, device engineering plays a key role in improving solar cells performance. Using the ternary strategy, the advantages of two non-fullerenes with good compatibility can be integrated into one device, which can improve the performance of the device simply and effectively. Our series of research results show that the introduction of the appropriate third component can not only expand the photon harvesting of the active layer, optimize photogenerated exciton distribution in the active layer to balance the charge transport, but also fine adjust phase separation degree to improve the efficiency of exciton dissociation. Ternary strategy is expected to be the first choice of the industrialization of organic photovoltaic device. The latest research work is described as follows: (1) Introducing high LUMO level acceptors to reduce energy loss: introducing medium band gap material MeIC as the third component into PM6:BTP-4F-12, the device efficiency is increased from 16.2% to 17.4%. The introduction of appropriate MeIC can simultaneously optimize photon harvesting, exciton dissociation and carrier transport in the active layer. In addition, appropriate amount of MeIC can effectively improve the luminescence quantum efficiency of the device, reduce the non-radiation energy loss, and promote the open circuit voltage of the device. This work proves that the ternary strategy is an effective way to reduce the energy loss of devices. (2) Preparation of high efficiency OPVs based on Y6 and its derivatives: based on high efficiency non-fullerene material Y6 and its derivative Y6-1O with good compatibility as acceptors and wide bandgap polymer material D18-Cl as donors, ternary organic photovoltaic devices with an efficiency of 17.9% were prepared. Compared with the binary system, the three photovoltaic parameters of the ternary system are improved simultaneously. In this work, the magneto-controlled photocurrent method was first introduced into the ternary system. It was concluded that the charge separation within the ternary system was more effective, which provided more solid evidence for analyzing the reasons for performance improvement of the ternary system.