A new thiazolo[5,4-d]thiazole-core organic chromophore with furan spacer (TP-FTzF-TP) was synthesized and PEDOT:PSS buffer layer was modified by graphene (Gr) for the efficient solution-processed bulk-heterojunction (BHJ) small molecule organic solar cells (SMOSCs). The introduction of furan as spacer in the thiazolo[5,4-d]thiazole-core based organic chromophore tuned the absorption and the electrochemical properties. The synthesized TP-FTzF-TP chromophore exhibited good optical parameters and a suitable HOMO/LUMO values of - 5.33 eV/-3.15 eV. The synthesized organic chromophore with triphenylamine as a strong electron-donor and furan spacer promoted the charge transfer and charge extraction in fabricated SMOSCs. The modification of PEDOT:PSS by Gr considerably increased the roughness of thin film. The power conversion efficiency (PCE) of similar to 3.63% was achieved by fabricated SMOSC device with ITO/Gr-PEDOT:PSS/TP-FTzF-TP:PC60BM (1:2, w/w)/Au architecture. It was found that the Gr-PEDOT:PSS as a buffer layer significantly enhanced PCE by two time factor as compared to the SMOSC device (PCE = similar to 2.13%) with pristine PEDOT:PSS layer.