Two effects of 1,8-diiodooctane on PTB7-Th:PC71BM polymer solar cells

• The effect of DIO on charge generation and charge transport were studied carefully.
• Positive effects of DIO for charge generation were proved by the results of IQE and Jph.
• Negative effects of DIO for charge transport were investigated according to the TOF-SIMS.

To obtain higher device performance, the ideal bulk heterojunction (BHJ) morphology should feature both nanophase separation to increase charge generation and bi-continuous percolating networks to increase charge transport. In this paper, solvent additive, 1,8-diiodooctane (DIO), was used in PTB7-Th:PC71BM blend to improve BHJ morphology. The effect of DIO on charge generation and charge transport were studied carefully. Experimental study indicated that the effect of DIO on charge generation and charge transport are conflicted. Positive effects of DIO, which were induced by nanophase separation for charge generation in BHJ, are proved by the results of internal quantum efficiency (IQE) and photocurrent density (Jph), and negative effects of DIO on charge transport has been investigated according to the time-of-flight secondary ion mass spectrometer (TOF-SIMS).

The addition of DIO resulted in smaller domains and a more finely interpenetrating BHJ morphology which were good to charge generation. The addition of DIO also caused donor material (PTB7-Th) migrates or diffuses toward the low work function cathode which was unfavorable for charge transport.Figure optionsDownload as PowerPoint slide