Department of Physics; Institute of Advanced Material
The effects of a solvent additive, 1,8-diiodooctane (DIO), on both hole and electron transport are investigated in a state-of-the-art bulk-heterojunction (BHJ) system, namely PTB7:PC71BM. For a polymer:fullerene weight ratio of 1:1.5, the electron mobility in the blend film increases by two orders of magnitude with the DIO concentration while almost no change is found in the hole mobility. For lower DIO concentrations, the electron mobility is suppressed because of large, but poorly connected PC71BM domains. For higher concentrations of DIO, the electron mobility is improved progressively and the hole mobility becomes the limiting factor. Between 1 and 5 vol%, the electron and hole mobilities are balanced. Using the Gaussian disorder model (GDM), we found that the DIO concentration modifies fundamentally the average hopping distances of the electrons. In addition, there exist alternative donor–acceptor ratios to achieve optimized PTB7:PC71BM based solar cells. It is demonstrated that the fullerene content of the BHJ film can be significantly reduced from 1:1.5 to 1:1 while the optimized performance can still be preserved.
admittance spectroscopy, bulk heterojunction, carrier transport, photovoltaics, solvent additives
Source Publication Title
Advanced Materials Interfaces
This is the peer reviewed version of the following article: Ho, Carr Hoi Yi, Qi Dong, Hang Yin, Winky Wing Ki Leung, Qingdan Yang, Harrison Ka Hin Lee, Sai Wing Tsang, and Shu Kong So. "Impact of solvent additive on carrier transport in polymer: Fullerene bulk heterojunction photovoltaic cells." Advanced Materials Interfaces 2.12 (2015):1500166, which has been published in final form at http://dx.doi.org/10.1002/admi.201500166. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Support for this work under the Research Grant Council of Hong Kong under Grant No. HKBU211412 was gratefully acknowledged. This work is also partially supported by the Research Grant Council of Hong Kong under Project No. T23-713/11.
Link to Publisher's Edition
Ho, Carr Hoi Yi, Qi Dong, Hang Yin, Winky Wing Ki Leung, Qingdan Yang, Harrison Ka Hin Lee, Sai Wing Tsang, and Shu Kong So. "Impact of solvent additive on carrier transport in polymer: Fullerene bulk heterojunction photovoltaic cells." Advanced Materials Interfaces 2.12 (2015): 1500166.