Combining chlorination and sulfuration strategies for high-performance all-small-molecule organic solar cells

Three small-molecule donors based on dithieno[2,3-d:2ʹ,3ʹ-dʹ]-benzo[1,2-b:4,5-bʹ] dithiophene (DTBDT) unit were designed and synthesized by side chain regulation with chlorinated or/and sulfurated substitutions (namely ZR1, ZR1-Cl, and ZR1-S-Cl respectively), along with a crystalline non-fullerene acceptor IDIC-4Cl with a chlorinated 1,1-dicyanomethylene-3-indanone (IC) end group. Energy levels, molar extinction coefficients and crystallinities of three donor molecules can be effectively altered by combining chlorination and sulfuration strategies. Especially, the ZR1-S-Cl exhibited the best absorption ability, lowest higher occupied molecular orbital (HOMO) energy level and highest crystallinity among three donors, resulting in the corresponding all-small-molecule organic solar cells to produce a high power conversion efficiency (PCE) of 12.05% with IDIC-4Cl as an acceptor.