An efficient strategy was provided by adopting different numbers of electron-deficient units (pyrimidyl and quinolyl) into parent coumarin sensitizers to obtain excellent absorption in the short-wavelength region (B2 band), which eventually improves the performance of DSSCs. Density functional theory calculations were performed on both free dyes and dye–TiO₂ complexes. As expected, introducing a single electron-deficient unit results in a positive influence on the power conversion efficiency (η) of DSSCs because of the larger short-circuit current density (J_sc is proportional to optical absorption (φ_LHE), charge separation, dye regeneration (φ_reg) and electron injection (φ_inject)) and the higher open circuit voltage (V_oc). The introduction of more pyrimidine facilitates charge separation and favors effective electron injection, whereas the second quinoline displays the opposite effect. The results give guidance to design promising candidates for future DSSCs applications.