Organic electroluminescent devices are disclosed. A representative device incorporates a substrate that comprises a control area and a sensitive area. A switch device and a driving device are disposed overlying the control area. A photo sensor is disposed overlying the sensitive area. An OLED element is disposed in the sensitive area and illuminating to the photo sensor. A capacitor is coupled to the photo sensor and the driving device, wherein a photo current corresponding to the brightness of the OLED element is generated in the photo sensor responsive to the OLED element illuminating the photo sensor such that a voltage of the capacitor is adjusted by the photo current to control the current passing through the driving device, thus changing the illumination of the OLED element.