Advancing the photovoltaic performance of all-polymer solar cells (APSCs) requires a comprehensive understanding of the dependence of the properties of photoactive blend films on the solvents used to process them. We have studied the correlation between the morphology of PTB7-Th:PNDI2OD-T2 blend films prepared using six different processing solvents. Three-dimensional (3D) transmission electron microscopy tomography (TEMT) revealed the influence of the 3D morphology of the PTB7-Th:PNDI2OD-T2 blend films on their photovoltaic performance. The high-performing toluene (TOL)- and o-xylene (XY)-processed blend films displayed power conversion efficiencies (PCEs) of ~4%, which contained nanoscopically networked fibrous PNDI2OD-T2 polymer domains. The films processed using the other solvents exhibited partly disconnected domains or unfavorable vertical phase separation. In addition, the use of N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), or N-methyl-2-pyrrolidone (NMP) as a solvent additive in XY solution resulted in a substantial improvement in the PCEs to 6.1%. This large enhancement was attributed to the formation of the better-interconnected narrower crystalline fibrillary structure of PNDI2OD-T2 chains with the aid of solvent additives, as clearly elucidated by 3D-TEMT imaging. This work highlights that APSCs processed from benign nonhalogenated solvents with appropriate additives can outperform APSCs processed from toxic halogenated solvents by affording a favorable blend morphology and that 3D TEMT imaging is a powerful and essential tool for characterizing the true morphology of photoactive layers.
Bibliographical noteFunding Information:
This work was supported by the National Research Foundation of Korea ( NRF-2018R1A5A1025594 , 2015M1A2A2056218 , 2019R1A2B5B01070463 , 2020R1A2C2014151 ) of the Ministry of Science and ICT , and Gwangju Institute of Science and Technology Research Institute (GRI) Grant. Experiments at PLS (Beamline 9A) were supported in part by MSIP and POSTECH.
All Science Journal Classification (ASJC) codes
- Renewable Energy, Sustainability and the Environment
- Materials Science(all)
- Electrical and Electronic Engineering