"Thermal annealing (TA) can lead to very different morphologies that directly impact the organic solar cells (OSCs) efficiency. This temperature treatment could improve bulk morphology, which reduce charge carrier recombination and, therefore, improving the photovoltaic performance of bulk heterojunction (BHJ). Here, very thin solid films (~ 300 pm) of DRCN5T:[70]PCBM blend, were analyzed through scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). DRCN5T is an electro-donor compound used in the OSCs active film, which reach ~10% of power conversion efficiency. These very thin solid films exhibit a worm-like pattern without thermal annealing (amorphous behavior), however after applying TA at 120°C, the small molecule crystallizes: its structural geometry become a well-defined organized one."