Composition tuning of a mixture of thienothiophene-based polymer (PTB7) and PC70BM using a novel additive, tetrabromothiophene (Br-ADD)

The addition of small amounts of additive (tetrabromothiophene, Br-ADD) tuned the vertical composition in an active layer, by selectively interacting with thiophene-based polymers. This tuned vertical distribution not only assured a high interfacial area but also comprised an acceptor-rich layer near the top, a donor-rich layer near the bottom and well-mixed layer between these two layers, which is good for polymer solar cells (PSCs).