We introduce a novel method to easily fabricate nanopatterns at ambient conditions using solvent-assisted soft nanolithography. For this purpose, a P3HT/PCBM bilayer, one of well-known standard models of solar cell systems, was chosen to optimize bilayer solar cells using the new lithographic technique. The nanopatterns of P3HT made using this method have improved device efficiency compared to planar bilayer heterojunction of the solar cell. The new patterning process creates solar cell devices with a greater than 2-fold increase in power conversion efficiency (PCE) compared to an otherwise equivalent, flat device. This improvement in efficiency is due to the increased interfacial area created by the patterning process. This result demonstrates the feasibility of extensive applications toward nanolithography, relevant to device fabrication, such as electronic devices.