Polycyclic Aromatic Lactam-Like Donors Synthesized upon C─H Activation Strategy for High-Efficiency Ternary Organic Solar Cells

The rapidly developed organic solar cells (OSCs) are largely driven by π-conjugated small-molecule and polymer materials in recent years. However, the organic photovoltaic materials served as the active layer are typically synthesized by multistep Stille or Suzuki cross-coupling reaction, which are neither cost-efficient nor atom-economic, and may bring toxicity concerns. Thus, it is imperative to develop easily accessible materials that do not involve organotin and organoboron reagents to promote the commercial application of OSCs. Herein, three small-molecule donors (Ph-RDN, N-RDN, and TT-RDN) comprising polycyclic aromatic lactams (PAL) core are designed and synthesized by direct C─H activation strategy and employed as the third components into the model PM6:Y6 photovoltaic systems. These donors show low-lying highest occupied molecular orbital energy levels, good crystallinity, and complementary absorption with the host system (PM6:Y6). The optimized ternary devices achieve higher power conversion efficiency (PCE) (17.01% for PM6:Ph-RDN:Y6, 16.58% for PM6:N-RDN:Y6, and 17.00% for PM6:TT-RDN:Y6) as compared with PM6:Y6 binary devices (15.67%), which are attributed to the higher charge mobilities, the more balanced charge transport, and the optimized morphology with a more well-defined fibrillar network. Therefore, PAL-based small-molecule donors, as a class of “greener” organic photovoltaic materials, can enhance the PCE of state-of-the-art OSCs.