Introduction: Chen Shuming and others from Southern University of Science and Technology have developed a series connected quantum dot light-emitting diode by using transparent conductive indium zinc oxide as the intermediate electrode. The diode can operate under positive and negative alternating current cycles, with external quantum efficiencies of 20.09% and 21.15%, respectively. In addition, by connecting multiple series connected devices, the panel can be directly driven by household AC power without the need for complex backend circuits. Under the drive of 220 V/50 Hz, the power efficiency of the red plug and play panel is 15.70 lm W-1, and the adjustable brightness can reach up to 25834 cd m-2.
Light emitting diodes (LEDs) have become the mainstream lighting technology due to their high efficiency, long lifespan, solid-state and environmental safety advantages, meeting the global demand for energy efficiency and environmental sustainability. As a semiconductor pn diode, LED can only operate under the drive of a low-voltage direct current (DC) source. Due to unidirectional and continuous charge injection, charges and Joule heating accumulate within the device, thereby reducing the operational stability of the LED. In addition, the global power supply is mainly based on high-voltage alternating current, and many household appliances such as LED lights cannot directly use high-voltage alternating current. Therefore, when LED is driven by household electricity, an additional AC-DC converter is required as an intermediary to convert high-voltage AC power into low-voltage DC power. A typical AC-DC converter includes a transformer for reducing the mains voltage and a rectifier circuit for rectifying the AC input (see Figure 1a). Although the conversion efficiency of most AC-DC converters can reach over 90%, there is still energy loss during the conversion process. In addition, to adjust the brightness of the LED, a dedicated driving circuit should be used to regulate the DC power supply and provide the ideal current for the LED (see Supplementary Figure 1b).
The reliability of the driver circuit will affect the durability of LED lights. Therefore, introducing AC-DC converters and DC drivers not only incurs additional costs (accounting for about 17% of the total LED lamp cost), but also increases power consumption and reduces the durability of LED lamps. Therefore, developing LED or electroluminescent (EL) devices that can be directly driven by household 110 V/220 V voltages of 50 Hz/60 Hz without the need for complex backend electronic devices is highly desirable.
In the past few decades, several AC driven electroluminescent (AC-EL) devices have been demonstrated. A typical AC electronic ballast consists of a fluorescent powder emitting layer sandwiched between two insulating layers (Figure 2a). The use of insulation layer prevents the injection of external charge carriers, so there is no direct current flowing through the device. The device has the function of a capacitor, and under the drive of a high AC electric field, the electrons generated internally can tunnel from the capture point to the emission layer. After obtaining sufficient kinetic energy, electrons collide with the luminescent center, producing excitons and emitting light. Due to the inability to inject electrons from outside the electrodes, the brightness and efficiency of these devices are significantly lower, which limits their applications in the fields of lighting and display.
In order to improve its performance, people have designed AC electronic ballasts with a single insulation layer (see Supplementary Figure 2b). In this structure, during the positive half cycle of AC drive, a charge carrier is directly injected into the emission layer from the external electrode; Efficient light emission can be observed by recombination with another type of charge carrier generated internally. However, during the negative half cycle of AC drive, the injected charge carriers will be released from the device and therefore will not emit light.Due to the fact that light emission only occurs during the half cycle of driving, the efficiency of this AC device is lower than that of DC devices. In addition, due to the capacitance characteristics of the devices, the electroluminescence performance of both AC devices is frequency dependent, and optimal performance is usually achieved at high frequencies of several kilohertz, which makes them difficult to be compatible with standard household AC power at low frequencies (50 hertz/60 hertz).
Recently, someone proposed an AC electronic device that can operate at frequencies of 50 Hz/60 Hz. This device consists of two parallel DC devices (see Figure 2c). By electrically short circuiting the top electrodes of the two devices and connecting the bottom coplanar electrodes to an AC power source, the two devices can be alternately turned on. From a circuit perspective, this AC-DC device is obtained by connecting a forward device and a reverse device in series. When the forward device is turned on, the reverse device is turned off, acting as a resistor. Due to the presence of resistance, the electroluminescence efficiency is relatively low. In addition, AC light-emitting devices can only operate at low voltage and cannot be directly combined with 110 V/220 V standard household electricity. As shown in Supplementary Figure 3 and Supplementary Table 1, the performance (brightness and power efficiency) of reported AC-DC power devices driven by high AC voltage is lower than that of DC devices. So far, there is no AC-DC power device that can be directly driven by household electricity at 110 V/220 V, 50 Hz/60 Hz, and has high efficiency and long lifespan.
Chen Shuming and his team from Southern University of Science and Technology have developed a series connected quantum dot light-emitting diode using transparent conductive indium zinc oxide as the intermediate electrode. The diode can operate under positive and negative alternating current cycles, with external quantum efficiencies of 20.09% and 21.15%, respectively. In addition, by connecting multiple series connected devices, the panel can be directly driven by household AC power without the need for complex backend circuits.Under the drive of 220 V/50 Hz, the power efficiency of the red plug and play panel is 15.70 lm W-1, and the adjustable brightness can reach up to 25834 cd m-2. The developed plug and play quantum dot LED panel can produce economical, compact, efficient, and stable solid-state light sources that can be directly powered by household AC electricity.
Taken from Lightingchina.com
Post time: Jan-14-2025