Speaker: Yongfang Li
Affiliation: Institute of Chemistry, Chinese Academy of Sciences

Recent Research Progress of Photovoltaic Materials for High Performance Polymer Solar Cells

Polymer solar cells (PSCs) have attracted great attention in the past decade, because of the advantages of simple device structure, light weight and capability to be fabricated into flexible and semitransparent devices. The key photovoltaic materials of PSCs are conjugated polymer donors and the fullerene or non-fullerene acceptors. Recently, the nonfullerene n-type organic semiconductor (n-OS) acceptors have been developed quickly. In this lecture, I will report our recent research progress on the conjugated polymer donor materials, nonfullerene n-type conjugated polymer acceptor and n-OS acceptor materials. For the conjugated polymer donors, we developed a series of medium bandgap 2D-conjugated D-A copolymers based on bithienyl-benzodithiophene (BDTT) as donor unit and fluorobenzotriazole (FBTA) as acceptor unit to match with the low bandgap n-OS acceptor. The D-A copolymer donors possess complementary absorption spectra and matching electronic energy levels with ITIC acceptor. By side chain engineering (alkyl2, alkylthio3 tri-alkylsilyl4 and fluorine5 substitution) on the thiophene conjugated side chains of the medium bandgap polymers, the power conversion efficiency (PCE) of the PSCs with the polymers as donor and ITIC as acceptor reached 9~11%2-5. For the n-type polymer acceptor, we synthesized a new strong absorption copolymer of the A-D-A structured n-OS unit and thiophene unit, and the PCE of the all polymer PSCs based on the polymer acceptor reached 9.19%6. For the n-OS acceptors, by side chain isomerization of ITIC, we further improved the PCE of the nonfullerene PSCs to 11.77%7 and 12.03%.8 Our results indicate that the PSCs are promising for future application.

About the Speaker

Prof. Yongfang Li obtained his Ph.D. degree from Fudan University (1986). He has been a Professor of Institute of Chemistry, Chinese Academy of Sciences (ICCAS) since 1993. Prof. Li has published two books, more than 10 book chapters and more than 600 research papers in the fields of conjugated polymer optoelectronic materials and devices, electrochemistry of conducting polymers and semi-conductor nanocrystals. The published papers have been cited by others for more than 28000 times, H-factor: 86. In addition, he won some awards such as Second-Grade National Award of China on Natural Sciences, Young and Middle-aged Specialist with Outstanding Contributions in Natural Science, First-Grade Award of Beijing City on Science and Technology and Macro2012 Lecture Award. He was selected as an Academician of Chinese Academy of Sciences (2013). His present research interests include polymer solar cells and related photovoltaic materials (including conjugated polymer donor and n-type organic semiconductor acceptor) and interfacial buffer layer materials.