It is well known that most important electronic devices use Schottky junctions and heterojunctions. Unfortunately there is not an advanced book introducing heterojunctions systematically. This book fills the gap. It is an ideal and valued reference for researchers and graduate students focusing on organic thin film devices like organic light-emitting diodes (OLEDs), organic photovoltaic (OPV) cells, and organic field-effect transistors (OFETs). Instructors can use the book as a supplementary text for a semiconductor physics or organic electronics course, giving students a better feel for the application of organic thin film devices.