Banana-shaped electron acceptors with an electron-rich core fragment and 3D packing capability

The emergence of Y6-type nonfullerene acceptors has greatly enhanced the power conversion efficiency (PCE) of organic solar cells (OSCs). However, which structural feature is responsible for the excellent photovoltaic performance is still under debate. In this study, two Y6-like acceptors BDOTP-1 and BDOTP-2 were designed. Different from previous Y6-type acceptors featuring an A-D-AMODIFIER LETTER PRIME-D-A structure, BDOTP-1, and BDOTP-2 have no electron-deficient AMODIFIER LETTER PRIME fragment in the core unit. Instead, there is an electron-rich dibenzodioxine fragment in the core. Although this modification leads to a marked change in the molecular dipole moment, electrostatic potential, frontier orbitals, and energy levels, BDOTP acceptors retain similar three-dimensional packing capability as Y6-type acceptors due to the similar banana-shaped molecular configuration. BDOTP acceptors show good performance in OSCs. High PCEs of up to 18.51% (certified 17.9%) are achieved. This study suggests that the banana-shaped configuration instead of the A-D-AMODIFIER LETTER PRIME-D-A structure is likely to be the determining factor in realizing high photovoltaic performance.

Automated summary

The emergence of Y6-type nonfullerene acceptors has greatly improved the power conversion efficiency of organic solar cells. However, the impact of different structural features on the excellent photovoltaic performance is still debated. In this study, two new Y6-like acceptors were designed, and it was found that the banana-shaped molecular structure is likely to be the determining factor for achieving high photovoltaic performance.