Effects of Additives on Crystallization in Thin Organic Films

Controlling the shape and growth of crystals in molecular organic solids has ramifications impacting diverse fields, but remains challenging to fully exploit. Here, crystal shapes in organic thin films are manipulated from aspect ratios of 1 to over 50, with corresponding growth rates decreased by an order of magnitude simply by mixing a structurally dissimilar minority species into the film. These effects are mapped with composition and temperature in mixtures of two model small-molecular-weight organic compounds, revealing a continuous variation in crystal shape and growth rate. Other combinations of molecules are discussed, showing additive shape selection in multicomponent mixtures and enabling customization of crystal shape.