High performance all-polymer solar cells employing systematically tailored donor polymers

• High performance (PCE = 5.35%) achieved for all-PSCs through introduction of electron-withdrawing fluorine atoms to polymer acceptor unit and change the alkyl side chain in polymer donor unit.
• Systematical modifications on the chemical structure of the donor polymers in all-PSCs.
• Investigation of introduction of electron-withdrawing fluorine atoms to polymer acceptor unit effect on optical property, polymer coplanarity, intermolecular packing and balanced carrier transport.
• Investigation of change alkyl side chain in polymer donor unit effect on film morphology and hole transport.

We successfully designed and synthesized a series of BDT-Qx-T based polymers as the donor polymer used in all polymer solar cells (all-PSCs). Their properties were finely tuned by side-chain modification and the introduction of electron-withdrawing fluorine atoms to polymer acceptor unit. Then we systematically investigated the effect of molecular structure on the polymer morphology and photovoltaic properties in all-PSCs. We revealed that the fluorination can optimize polymer energy level and improve the polymer coplanarity, leading to enhanced intermolecular packing and balanced carrier transport. Meanwhile, the substitution of dodecyl for 2-ethylhexyl side chains can result in improved film morphology and hole transport. As a result of the synergistic effect between fluorination and side-chain modification, we achieved a high PCE of 5.35% for the optimized all-PSCs. More importantly, our approach may become a general and effective way to tailor the polymer molecular structure for achieving high performance all-PSCs.

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