Novel 2-hexylthieno[3,2-b]thiophene-containing conjugated molecules have been synthesized via a reduction reaction using tin chloride in an acidic medium. They exhibited good solubility in common organic solvents and good self-film and crystal-forming properties. The single-crystalline objects were fabricated by a solvent slow diffusion process and then were employed for fabricating field-effect transistors (FETs) along with thinfilm transistors (TFTs). TFTs made of 5 and 6 exhibited carrier mobility as high as 0.10-0.15 $cm^2V^{-1}s^{-1}$. The single-crystal-based FET made of 6 showed 0.70 $cm^2V^{-1}s^{-1}$ which was relatively higher than that of the 5-based FET (${mu}=0.23cm^2V^{-1}s^{-1}$). In addition, we fabricated organic photovoltaic (OPV) cells with new 2-hexylthieno [3,2-b]thiophene-containing conjugated molecules and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester ($PC_{61}BM$) without thermal annealing. The ternary system for a bulk heterojunction (BHJ) OPV cell was elaborated using $PC_{61}BM$ and two p-type conjugated molecules such as 5 and 7 for modulating the molecular energy levels. As a result, the OPV cell containing 5, 7, and $PC_{61}BM$ had improved results with an open-circuit voltage of 0.90 V, a short-circuit current density of 2.83 $mA/cm^2$, and a fill factor of 0.31, offering an overall power conversion efficiency (PCE) of 0.78%, which was larger than those of the devices made of only molecule 5 (${eta}$~0.67%) or 7 (${eta}$~0.46%) with $PC_{61}BM$ under identical weight compositions.