1. Field of the Invention
The present invention relates to a donor film for a laser induced thermal imaging method, a light emitting device using the same, and a method of manufacturing the light emitting device, and more particularly to, a donor film for a laser induced thermal imaging method capable of improving optical efficiency and optical extraction by forming a pattern having a predetermined step difference on a light to heat conversion layer (LTHC), a light emitting device using the same, and a method of manufacturing the light emitting device.
2. Description of the Related Art
In general, a light emitting device includes a first electrode, a second electrode, and an active layer interposed between the first electrode and the second electrode. An active layer includes an emission layer, a hole injecting layer, a hole transporting layer, an electron transporting layer, and an electron injecting layer. The light emitting device having the above structure is divided into an organic light emitting device and an inorganic light emitting device according to whether the active layer is made of an organic material or an inorganic material. The organic light emitting device is divided into a high molecular organic light emitting device and a low molecular organic light emitting device.
In order to realize the full color of the above-described organic light emitting device, the active layer that constitutes the organic light emitting device must be patterned by each color. In order to pattern the active layer, an inkjet printing method or a laser induced thermal imaging (LITI) method is mainly used. In the above-described patterning methods, the LITI method is a dry process and the inkjet printing method is a wet process. It is possible to more precisely pattern the active layer using the LITI process that is the dry process.
In order to form an organic active layer using the LITI process, a substrate (hereinafter, referred to as an acceptor substrate) on which a first electrode is formed, a donor film provided on the acceptor substrate to transcribe the organic active layer, and a laser that provides light on the donor film.
The manufacturing processes of laminating a transfer layer on an acceptor substrate using a donor film for a laser induced thermal imaging method according to a conventional art is described below.
A donor film includes a base substrate, a light to heat conversion layer (LTHC), a buffer layer, and a transfer layer in the form of a film made of an organic material. The transfer layer includes an emission layer, a hole transporting layer, a hole injecting layer, an electron transporting layer, and an electron injecting layer.
In order to laminate the transfer layer on an acceptor substrate using the LITI process, first, the donor film on which the transfer layer is formed is positioned on the acceptor substrate. To be specific, the donor film is positioned so that the transfer layer contacts the first electrode of the acceptor substrate. Next, when laser is radiated onto the base substrate of the donor film, the LTHC layer converts laser radiation into heat to emit heat so that the transfer layer is transcribed onto the first electrode of the acceptor substrate. Through the above-described processes, the transfer layer made of an organic material is laminated on the acceptor substrate so that it is possible to form the organic active layer of an organic light emitting device. As described above, when the transfer layer in the form of the film made of the organic material is transcribed onto the first electrode of the acceptor substrate, it is possible to easily form the hole injecting organic layer, the hole transporting organic layer, the electron transporting organic layer, and the electron injecting organic layer as well as the organic emission layer.
However, recently, it is necessary to easily form the organic active layer using the LITI process and to obtain the lamination pattern of the organic active layer that provides better emission efficiency than the emission efficiency provided by the active layer having an almost flat surface and that facilitates optical extraction.