Over 15% Efficiency Polymer Solar Cells Enabled by Conformation Tuning of Newly Designed Asymmetric Small-Molecule Acceptors

Abstract

The prosperous period of polymer solar cells (PSCs) has witnessed great progress in molecule design methods to promote power conversion efficiency (PCE). Designing asymmetric structures has been proved effective in tuning energy level and morphology, which has drawn strong attention from the PSC community. Two hepta-ring and octa-ring asymmetric small molecular acceptors (SMAs) (IDTP-4F and IDTTP-4F) with S-shape and C-shape confirmations are developed to study the relationship between conformation shapes and PSC efficiencies. The similarity of absorption and energy levels between two SMAs makes the conformation a single variable. Additionally, three wide-bandgap polymer donors (PM6, S1, and PM7) are chosen to prove the universality of the relationship between conformation and photovoltaic performance. Consequently, the champion PCE afforded by PM7: IDTP-4F is as high as 15.2% while that of PM7: IDTTP-4F is 13.8%. Moreover, the S-shape IDTP-4F performs obviously better than their IDTTP-4F counterparts in PSCs regardless of the polymer donors, which confirms that S-shape conformation performs better than the C-shape one. This work provides an insight into how conformations of asymmetric SMAs affect PCEs, specific functions of utilizing different polymer donors to finely tune the active-layer morphology and another possibility to reach an excellent PCE over 15%.