LAUSR

Core engineering of small molecule acceptors (SMAs) is crucially important for enhancing device efficiency for nonfullerene organic solar cells (NF-OSCs). The most commonly used SMAs (e.g., ITIC) utilize indacenodithieno[3,2-b]thiophene (IDTT) as the central core, which has restricted their absorption ranges due to the weak electron-donating ability and short conjugation length. Here, we fused two electron-rich units, namely cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT) and dithieno[3,2-b:2′,3′-d]pyran (DTPR), into the cores for constructing low-bandgap SMAs. The resulting CPDT-4Cl and DTPR-4Cl molecules exhibit extended nonacyclic central cores and strengthened intramolecular transfer (ICT) effect, resulting in red-shifted absorption (up to ∼950 nm) and up-shifted HOMO levels compared with IDTT-4Cl. Consequently, the NF-OSCs based on PTB7-Th:CPDT-4Cl and PTB7-Th:DTPR-4Cl achieved higher PCEs of 12.15% and 10.75%, respectively, than those of the PTB7-Th:IDTT-4Cl ones (7.70%). Notably, high short-circuit current densities (JSC) of 23–25 mA cm−2 were obtained by the CPDT-4Cl and DTPR-4Cl-based devices, indicating the great potential of the electron-donating CPDT and DTPR as promising building blocks to construct high-performance low-bandgap SMAs.