Organic Light Emitting Diodes by Molecular Beam Epitaxy

The dream of using organic materials in high performance optoelectronic devices is rapidly becoming a reality. These include, but are not limited to, organic light emitting devices (OLEDs); photovoltaic cells; and photo detectors. Such organic devices have reached performance levels comparable to or, in some cases, even better than their inorganic counterparts. They are inexpensive, can be fabricated on flexible substrates and can be easily modified with the addition of a large variety of chemical functional groups.

My project was focused on the fabrication of organic light emitting diodes and Fullerene based photocells grown by molecular beam epitaxy. To this end we put together a high-vacuum chamber for thermal evaporation of organic compounds, which was optically coupled to a remote diode-array spectrophotometer. This allows for acquisition of absorption spectra during thin film deposition and thus provides immediate feedback regarding the film thickness and composition. Typical device geometry consists of a transparent, yet conductive, indium-tin-oxide substrate on which we deposit an active organic layer sandwiched between a hole-transport layer and an electron-transport layer. The active layer is a strongly luminescent organic material (in the case of OLEDs), or a strongly absorbing material (in the case of photocells). On top of this we deposit a thin aluminum electrode layer. The OLEDs would emit bright light when a small voltage is applied across it, while photocells produce a couple of volts when exposed to sunlight.
Our research will aid in the optimization of these organic layers.