Influence of 3D morphology on the performance of all-polymer solar cells processed using environmentally benign nonhalogenated solvents
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We studied the effect of processing solvents on the photovoltaic properties and the morphology of PTB7-Th:PNDI2OD-T2 blend films. The blend films prepared by toluene and o-xylene showed power conversion efficiencies (PCEs) of ~4%, while those prepared by halogenated solvents showed PCEs of ~3%. Using N-dimethylformamide, N,N-dimethylacetamide, or N-methyl-2-pyrrolidone as a solvent additive in o-xylene solution resulted in a significant improvement of the PCEs to 6.1%. Three-dimensional (3D) transmission electron microscopy tomography (TEMT) revealed the correlation of the 3D morphology and photovoltaic performance of the PTB7-Th:PNDI2OD-T2 blend films. This experiment suggests that all-polymer solar cells (APSCs) prepared by benign nonhalogenated solvents with appropriate additives can outperform ASPCs prepared by toxic halogenated solvents and 3D TEMT imaging is a useful analysis for characterizing the morphology of photoactive layers.