LAUSR

Novel cores for high performance non-fullerene acceptors (NFAs) remain to be developed. In this work, two new n-type nitrogen-containing organic heterocyclic NFAs, namely BDTN-BF and BDTN-Th, were designed and synthesized, based on a new seven fused-ring core (BDTN) with two different end-capping groups. As a result, BDTN-BF possessed similar absorption spectra in solution and solid state to BDTN-Th, but slightly higher maximum molar extinction coefficient. Manufacturing the polymer solar cells (PSCs) with PM6 as donor, the photovoltaic performance of BDTN-BF and BDTN-Th was investigated. PM6:BDTN-BF based device achieved the highest power conversion efficiency (PCE) of 11.54% with a high Jsc of 20.20 mA cm-2, a FF of 61.46%, and a large Voc of 0.93 V, and the energy loss (Eloss) was calculated to be 0.48 eV. Comparatively, PM6:BDTN-Th based device achieved the maximum PCE value of only 3.53% due to inadequate Jsc and FF. The higher Jsc and FF for PM6:BDTN-BF-based device was mainly put down to the effective electron transfer from PM6 to BDTN-BF, more balanced μh/μe, higher electron mobility of neat film, better charge collection and dissociation efficiency, and more favorable morphology. These results demonstrate that the acceptors with nearly identical absorption spectra could result in significant difference of photovoltaic performance, which stress the importance of end-capping units. Furthermore, few NFAs based devices achieve large Voc and high Jsc simultaneously as one based on PM6:BDTN-BF, indicating that nitrogen hybridization of NFAs may be an efficient strategy to realize high and balanced Voc and Jsc.