Tailoring Morphology Compatibility and Device Stability by Adding PBDTTPD-COOH as Third Component to Fullerene-Based Polymer Solar Cells

The crystallinity and morphology of polymer and fullerene have a profound influence on the performance of bulk heterojunction (BHJ) organic photovoltaic devices. The poor compatibility of donor and acceptor molecules in the BHJs hinders the further improvement of the device performance and stability in organic solar cells. In this work, the conjugated polymer PBDTTPD-COOH is introduced as a third component into BHJ films of PTB7-Th:PC₇₁BM and PffBT4T-2OD:PC₇₁BM to improve the crystallinity and morphology. The crystallinity of both donor polymers is enhanced and more face-on orientated crystals are observed in the corresponding films, which is correlated with the improvement of the current density of the related solar cells. Also, the improved BHJ morphology leads to an increased fill factor. Furthermore, the device stability significantly increases by the addition of the third component PBDTTPD-COOH. The T80 lifetime value is enhanced 10 times in the doped devices as compared with the binary solar cells in the case of the PTB7-Th:PC₇₁BM series.