Morphology study on ternary blend polymer solar cell to achieve improved device performance

Ternary blend solar cells are considered presents one route to construct the devices with a broad absorption of the solar spectrum. However, the morphological studies on such mixtures have been limited. Here, the morphology of P3HT/PCPDTBT/PC₆₁BM ternary blend thin films were studied. By adjusting the blending ratio of two polymers, P3HT molecular weight, thermal annealing time and spin-coating solvents, the crystallinity of both polymers and phase separation among each component were controlled. It was found that a high crystallinity of the polymers is important for good device performance. Due to the crystallization of the polymers and the immiscibility between P3HT and PCPDTBT, a hierarchical morphology was generated that mimicked a tandem cell connected in parallel and extended the absorption. In addition, the amorphous PCPDTBT was found to guide the orientation of P3HT nanocrystals before they merged into fibrils, and it also served as a photosensitizer to form a cascade energy level alignment. Therefore, the two polymers worked synergistically to achieve the improved device performance relative to the binary reference.