The realization of stable, high efficiency blue organic light emitting devices (OLEDs) remains
challenging. The efficiency of blue fluorescent OLEDs is fundamentally limited, and blue
phosphors are typically less stable. We discuss potential solutions to these problems. We show
that device engineering can be used to optimize the color of a relatively stable and efficient bluegreen
phosphor. In addition, we demonstrate the ability to manipulate the fraction of excitons
which form as singlets in fluorescent materials by inserting a mixing layer that affects only the
precursors to excitons.