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Abstract title Molecular and Device Engineering towards Efficient All-Polymer Solar Cells with PCE over 7%
Author Prof. Yuan, Jianyu, SUZHOU, China (Presenting Author)
Co-author(s) Ma, Wanli
Abstract text

In this prospective talk, we will disclose the synthesis and characterization of a series of polymer-polymer bulk hetero-junction (BHJ) blends, which incorporate benzodithiophene (BDT)-based donor-acceptor (D-A) copolymers as donor, naphthalene diimide (NDI)-based D-A copolymers as acceptor. By introducing different numbers of alkyl aromatic side chains to the donor polymers, together with crstallinity modification on acceptor polymers, the performance of all-polymer solar cells was greatly improved and optimized power conversion efficiency (PCE) over 6.0% was obtained with a high Voc of 1.0 V. Compared to the widely used fullerene derivative acceptor, the polymer acceptor can harvest more photons up to NIR region, and we further investigated the widely current and fill factor losses in current all-polymer solar cell devices. Assisted by ultrafast transient transmission spectroscopy, 2d-GIWAXS and other morphological characterization technique, we reveal the origin of loss mechanism in polymer-polymer solar cell devices and quantified the hole transfer efficiency from acceptor polymer to donor polymer. In addition, through systematic morphology optimization including processing additives and third component ternary device structure, we further improve our all-polymer system to 7.1 %, we have shown that the introduction of the third component and processing solvent additives are beneficial for the light absorption, intermolecular π-π stacking and hence improves the polymer crystallinity as well as hole mobility. Finally, we first revealed the preparation of high-efficiency homo-tandem all-polymer solar cells, exhibiting 40 % PCE enhancement compared to the single junction solar cells. All these findings are particularly important when considering further molecular design, device processing and long-term organic solar cells durability under various conditions.