Design and synthesis of novel low bandgap asymmetrical squaraine derivatives for high-performance small-molecule organic solar cells

Yao Chen1,  Youqin Zhu2,  Yan Huang1,  Suling Zhao2,  Zhiyun Lu1
1College of Chemistry, Sichuan University, 2Institute of Optoelectronics Technology, Beijing Jiaotong University

Abstract

Owing to their intense absorption in Vis-NIR regions and good photochemical stability, squaraine dyes (SQ) have drawn much attention in small-molecule organic solar cell (SMOSC) applications, and high-performance SQ-based SMOSCs with record power conversion efficiency (PCE) of 5.50% has been achieved.1 However, the squaraine dye used in this device has a symmetrical molecular structure (D-A-D, SSQ); while compared to SSQ, asymmetrical squaraines (ASQ, D-A-D’) should be more promising due to their more plenty room for molecular tailoring. In this study, we report the design and synthesis of a series of novel ASQs with their two electron-donating aryls directly linked to the electron withdrawing squaric acid cores. Through rational molecular design, we have developed an ASQ dye with bandgap of as low as 1.33 eV together with an intense and broad absorption band in 550-950 nm. Note that this is the lowest bandgap among ASQs reported so far for SMOSC applications. Excitingly, solution-processed SMOSC with it as electron donor material exhibits excellent short circuit current (Jsc) of 12.03 mA cm-2 and high PCE of 4.35%, both are the highest values among ASQ-based BHJ-SMOPVs.2 All these preliminary results indicated that ASQ derivatives should be quite promising organic photovoltaic electron-donor materials.

Acknowledgement We acknowledge National Natural Science Foundation of China (Project No.21432005, 21190031 and 21372168) and the Research Fund for the Doctoral Program of Higher Education (No.20120009130005) for financial support.

References

1. G. Wei, S. Wang, K. Sun, M. E. Thompson and S. R. Forrest, Adv. Energy Mater., 2011, 1, 184-187.

2. (a) D. Yang, Q. Yang, L. Yang, Q. Luo, Y. Chen, Y. Zhu, Y. Huang, Z. Lu and

S. Zhao, Chem. Commun., 2014, 50, 9346-9348; (b) D. Yang, Q. Yang, L. Yang, Q. Luo, Y. Huang, Z. Lu and S. Zhao, Chem. Commun., 2013, 49, 10465-10467; (c) L. Yang, Q. Yang, D. Yang, Q. Luo, Y. Zhu, Y. Huang, S. Zhao and Z. Lu, J. Mater. Chem. A, 2014, 2, 18313-18321.

Corresponding author’ E-mail: huangyan@scu.edu.cn