CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No. 10-2019-0096286 filed on Aug. 7, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

Technical Field

The present disclosure relates to an organic light emitting display device, and more particularly, to a transparent organic light emitting display device.

Description of the Related Art

Recently, as it enters an information era, a display field which visually expresses electrical information signals has been rapidly developed and in response to this, various display devices having excellent performances such as thin-thickness, light weight, and low power consumption have been developed.

Specific examples of such a display device include a liquid crystal display device (LCD), a field emission display device (FED), and an organic light emitting display device (OLED).

Each of a plurality of pixels which configures an organic light emitting display device (OLED) includes an organic light emitting diode configured by an organic light emitting layer between an anode and a cathode and a pixel circuit which independently drives the organic light emitting diode. The pixel circuit includes a switching thin film transistor (hereinafter, abbreviated as a TFT), a driving TFT, and a capacitor. Here, the switching TFT charges a data voltage to the capacitor in response to a scan pulse and the driving TFT controls a driving current amount which is supplied to the organic light emitting diode (OD) in accordance with a data voltage charged in the capacitor to adjust an emission amount of the organic light emitting diode.

Recently, in order to implement a head up display (HUD) for a vehicle, a transparent organic light emitting display device (transparent OLED) is being developed. Transparent substrates may be applied to both an upper substrate and a lower substrate of the transparent OLED.

BRIEF SUMMARY

The inventors have realized that according to the conventional art, when the transparent substrate is applied to the organic light emitting display device (OLED), external light such as sunlight may be irradiated onto a plurality of TFTs included in the pixel circuit through the transparent substrate. Specifically, external light may be irradiated onto a respective active layer of the plurality of TFTs through the transparent substrate.

When external light is irradiated to the respective active layer of the plurality of TFTs, a light leakage current is generated in the active layer of the plurality of TFTs. This further causes to change an S-factor of the plurality of TFTs and a threshold voltage of the plurality of TFTs. As a result, a gray-level expressiveness of the organic light emitting display device (OLED) may be degraded. Further, a driving current at a start timing and a driving current at an end timing are changed in one frame so that even in one frame, a constant gray-level cannot be expressed. Based on the inventors work in fully locating and appreciating these issues, they have proposed solutions as described herein.

The present disclosure provides an organic light emitting display device that includes a transparent substrate but that blocks a light leakage current of a plurality of TFTs. In addition, a transparent organic light emitting display device according to the present disclosure maintains a constant gray-level in one frame. This is made possible because a driving current at a start timing and a driving current at an end timing are not changed in the frame.

Other benefits of the present disclosure will be readily understood by those skilled in the art and other benefits not mentioned above would will be understood by those skilled in the art from the following descriptions.

In one or more embodiments, an organic light emitting display device includes a display panel including a plurality of pixels disposed on a substrate, and each of the plurality of pixels includes an organic light emitting diode and a pixel circuit which controls the driving of the organic light emitting diode. The pixel circuit includes: a driving TFT which supplies a driving current to the organic light emitting diode; a sampling TFT which samples a threshold voltage of the driving TFT; a first initializing TFT which supplies an initialization voltage to one electrode of the organic light emitting diode; and a storage capacitor which stores a voltage applied to the driving TFT, and at least one of the driving TFT, the sampling TFT, and the first initializing TFT includes a shielding electrode disposed between the substrate and the respective active layer of the various transistors. Therefore, even though the external light is irradiated onto a transparent substrate, a full white gray-level and a full black gray-level can be expressed so that the gray-level expressiveness may not be degraded.

In one or more embodiments, an organic light emitting display device includes an organic light emitting diode formed over a substrate and a pixel circuit which controls the driving of the organic light emitting diode. The pixel circuit includes: a driving TFT which is connected to one electrode of the organic light emitting diode; a switching TFT which is connected to a gate electrode of the driving TFT and a data line; and an initializing TFT which is connected to one electrode of the organic light emitting diode and an input terminal of an initialization voltage. At least one of the driving TFT, the switching TFT, and the initializing TFT includes a gate electrode disposed above the active layer and a shielding electrode disposed below the active layer. Therefore, even though external light is irradiated, a gray-level expressed for one frame may be constantly maintained.

Other detailed matters of the embodiments are included in the detailed description and the drawings.

According to the organic light emitting display device of the present disclosure, the shielding electrode is disposed between the transparent substrate and the active layer to block a light leakage current of the plurality of TFTs. Accordingly, in the organic light emitting display device of the present disclosure, a change in an S-factor of the plurality of TFTs and a change in a threshold voltage of the plurality of TFTs are suppressed to enhance a gray-level expressiveness.

According to the organic light emitting display device of the present disclosure, the shielding electrode is disposed between the transparent substrate and the active layer to stably maintain a gray-level expressed for one frame.

The effects according to the present disclosure are not limited to the contents exemplified above, and more various effects are included in the present specification.

