Using Spatial Confinement to Decipher Polymorphism in Organic Semiconductors p-DTS(FBTTh2)2

Many molecular semiconductors show a pronounced polymorphism; i.e. they can adopt different crystal arrangements depending, e.g., on temperature, pressure, and selected solidification pathways. This renders reliable fabrication of molecular semiconductor devices challenging, as minute changes in processing can lead to numerous structures and, hence, optoelectronic responses. Here, we demonstrate using the example of p-DTS(FBTTh2)2 that spatial confinement at the nanoscale can be exploited to detect specific polymorphs and the conditions under they form. A new polymorph exhibiting a higher charge-carrier mobility compared to previously reported p-DTS(FBTTh2)2 crystal forms is found at elevated temperatures and high degree of confinement, illustrating the benefit of our approach and promising that spatial confinement will find wide-spread application to understand and control polymorph formation in organic semiconductors.