Seed-induced Nanostructuring of Heteroepitaxial Molecular Semiconductor Thin Films for Enhanced Optoelectronic Response

Controlled growth of molecular semiconductor thin films with specific ordering and nanostructuring is crucial for devising next-generation organic optoelectronics with enhanced performance. A highly ordered crystalline organic thin films can be an ideal active layer for electronic devices owing to its improved charge transport ability. Despite tremendous efforts to achieve high quality crystalline active layers, most superior performances were realized in single crystal states rather than films, even though the film is more desirable for the device applications. This is critical for most molecular semiconductors with complicated molecular structure, such as twisted conformation or with bulky side chains, which show greater electronic properties in its crystalline phase, but it is particularly difficult to form crystalline films directly on inert substrates. Here, we demonstrate an unprecedented approach by the incorporation of nucleation seed layer that creates crystalline nanostructures of a molecular semiconductor that is observed to have an intrinsic proclivity to form amorphous films; our technique is also readily adaptable to scale-up ultrahigh vacuum deposition processes and can be immediately integrated into existing diode manufacturing routines to create uniform crystalline nanostructure over large areas. Crystalline films exhibited enhanced photophysical and electronic characteristics, compared to the amorphous counterparts. Finally, we show that large-area flexible optoelectronic devices including organic solar cells and light emitting diodes can be realized.