Thin polymer films for organic LED (OLED) and organic photovoltaic (OPV) applications are traditionally fabricated through "wet" processing methods such as spin-coating. In preparing spin-cast films, the presence of solvent can negatively impact the final product; as the solvent evaporates, pinholes and defects remain, acting as charge traps. Step-growth polymerization through vacuum co-deposition provides a solventless method for fabricating these devices. Through CVD, film composition and thickness can be precisely controlled, allowing for smooth, defect-free thin films.
Our goal is to vapor deposit a naphthalene-derived polyimide film (n-type organic semiconductor) supporting copper phthalocyanine (CuPc) particles (p-type organic semiconductor). A schematic showing our approach is provided below. By varying the deposition rates, and thereby controlling film morphology, a bulk p-n junction can be formed. This enables a mechanically stable polymer based OPV device without solvent defects. The presence of a bulk heterojunction may enhance hole and electron transport, allowing for increased efficiency compared to existing polymer-based OPVs.
