We have synthesized and characterized two low molecular weight organic molecules, namely, CS01 and CS03 having the benzo[c][1,2,5]thiadiazole-4,7-diamino core but differing in the number of aromatic rings at the amino groups. The molecules, when processed to make thin organic films, display absorbance up to the near-IR region (∼750 nm) and good hole mobility values. Upon mixing each organic semiconductor molecule with the fullerene derivative PC71BM, we monitored a strong quenching of the fluorescence emission. We assigned such a process to efficient charge transfer from the CS01 and CS03 molecules to the fullerenes. Moreover, fueled by this observation, we prepared organic solar cells and obtained, as a first attempt, efficiencies over 2% under 1 sun light simulated solar radiation. Furthermore, the film optimization through a careful solvent annealing process increased further the efficiencies up to 4.80% for CS01 and 5.12% for CS03. The observed increase in efficiency is due to a better morphology obtained through solvent annealing of the thin films. However, an in-depth analysis reveals that the solvent annealing led to a better hole mobility, but the electron mobility remains similar.