Highly efficient halogen-free solvent processed small-molecule organic solar cells enabled by material design and device engineering

Low bandgap small molecules, BDTTNTTR and BDTSTNTTR, with benzo[1,2-b:4,5-b′]dithiophene (BDT) as the central donor unit and naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT) as the second acceptor block, which were also π-bridged with terthiophenes on both sides, and end-capped with 3-ethylrhodanine electron-accepting groups, have been successfully synthesized for highly efficient small molecule solar cells (SM-OSCs). Based on tactful material design and device engineering, the resulting SM-OSCs processed with a halogen-free solvent of CS₂ exhibited a high efficiency of 11.53% with a very small energy loss of 0.57 eV.