  Research on organic thin-film transistors tends to focus on improvements in
device performance, but very little is understood about the ultimate limits of
these devices, the microscopic physical mechanisms responsible for their
limitations, and, more generally, the intrinsic transport properties of organic
semiconductors. These topics are now being investigated through the study of
transport in organic transistors realized using molecular single crystals of
unprecedented chemical purity and structural quality. These studies are
elucidating detailed microscopic aspects of the physics of organic
semiconductors and corresponding devices and have also led to unforeseen high
values for carrier mobility in these materials. Here, we discuss developments
in this area and present a brief outlook on future goals that have now come
into experimental reach.
