A quadrupole diketopyrrolopyrrole (DPP)-based small molecule (DPP4T-Cz) was designed and synthesized to enhance absorption coefficient, and then employed as the third component to improve the light harvesting of polymer solar cells based on a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Because of an enhanced absorption coefficient of more than 105 cm−1, the photon harvesting efficiency was improved effectively in the near infrared (near-IR) range by using only a small amount of DPP4T-Cz (3.4 wt%) into the P3HT:PCBM binary blend polymer solar cells. Interestingly, the photocurrent generation was also enhanced in the visible range by the long-range energy transfer from P3HT to DPP4T-Cz molecules. As a result, the short-circuit current density (JSC) and power conversion efficiency (PCE) of P3HT:PCBM:DPP4T-Cz ternary blend devices were enhanced by more than 30% compared to those of P3HT:PCBM binary control devices. These findings suggest that quadrupole DPP-based molecules are one of the effective light-harvesting materials for ternary blend polymer solar cells.