Engineering of polymerized small molecule acceptors for all-polymer solar cells: insights from DFT calculations*

All-polymer solar cells (all-PSCs) with polymerized small molecule acceptors (PSMAs) offer high mechanical and morphological stability, but they usually have low efficiency due to the availability of a small number of high-performance acceptor polymers, challenges in morphology control and fast charge recombination. Usually, most PSMAs feature small molecule acceptors polymerized using a thiophene linker. However, modifications of the π-linker at the molecular level can help improving their electronic and morphological properties.

In this work, we use Density Functional Theory (DFT) to characterize the electronic and conformational properties of two Y6-based PSMAs: PY-2T, based on a bithiophene π-linker, and PY-BTz, based on a dialkoxy-bithiazole linker. Devices based on the latter have shown enhanced efficiency due to improved charge transport and morphological properties of the donor-acceptor blend. By characterizing the electronic structure and conformational stability of the two polymers, we explain the superior performance of PY-BTz in terms of non-covalent conformation locks that induce backbone planarity, enhanced backbone conjugation and increased electron-deficiency at the linker site. The features identified in our work are expected to improve charge transport, packing and charge recombination losses in the BTz-based device.