Publication Date: 2003-Dec-18
The IP.com Prior Art Database
The invention relates to an electroluminescent device comprising a combination of a charge-transporting conjugated donor compound and a phosphorescent acceptor compound.
The invention further relates to the use of a charge-transporting conjugated donor compound in such a combination.
An electroluminescent (EL) device is a device which emits light when a suitable voltage is impressed on its electrodes. If the electroluminescent device has an organic material facilitating charge transport and/or light emission it is generally referred to
as an organic electroluminescent device. Organic electroluminescent devices can be made, by suitable choice of emissive material, to produce any color at low voltages. Further they are emissive, thin, light weight, flexible and/or of large area rendering such devices suitable for display, signage and lighting applications. An organic electroluminescent device may comprise organic compounds of relatively low molecular weight, also referred hereinafter as
small molecule electroluminescent devices, or compounds of high molecular weight, hereinafter also referred to as polymer electroluminescent devices.
It is generally held that in organic electroluminescent devices light emission proceeds by relaxation of excited states, in this context generally referred to as excitons, formed in the emissive material. The excitons are formed by recombination of holes and
electrons injected into the EL device by means of electrodes.
In order to achieve light emission upon application of a bias, at least charge transport of holes and electrons, formation of excitons and decay of excitons to the ground state by emission of photons is required. Electroluminescent devices wherein such charge transport and light emission takes place in different species are known as such. See e.g.
WO 01/41512. In such combinations a charge-transporting donor compound, in the art also referred to as a host compound, facilitates charge transport and a phosphorescent acceptor compound, in the art also referred to as a guest compound, facilitates light emission. EL devices comprising such combinations have attracted attention in the art because of their
alleged ability to harvest triplet excitons which in turn holds the promise of achieving high efficiencies. Accordingly, there is a need for providing EL devices having combinations of donor and acceptor compounds which, by selecting the emission level of the acceptor compound, can be made to emit red, yellow or orange light respectively, but also green light or light of higher frequency, such as blue, with high efficiency.
Like any molecular compound, the charge-transporting conjugated donor compound has excited states (excitons) which can be of the triplet or the singlet variety. More particular, there is a lowest-energy singlet and a lowest-energy triplet excited state.
It is an object of the i...