Three-phase electric power driven electoluminescent devices

Current power supply networks across the world are mostly based on three-phase electrical systems as an efficient and economical way for generation, transmission and distribution of electricity. Now, many electrically driven devices are relying on direct current or single-phase alternating current power supply that complicates utilization of three-phase power supply by requiring additional elements and costly switching mechanisms in the circuits. For example, light-emitting devices, which are now widely used for displays, solid-state lighting etc. typically operate with direct current power sources, although single-phase alternating current driven light-emitting devices have also gained significant attention in the recent years. Yet, light-emitting devices directly driven by a three-phase electric power has never been reported before. Benefiting from our precious work on coplanar electrodes structured light-emitting devices, in this article we demonstrate proof of a concept that light-emitting components can be driven by three-phase electric power without utilizing intricate back-end circuits and can compose state detection sensors and pixel units in a single device inspiring from three primary colors. Here we report a three-phase electric power driven electroluminescent devices fabricated featuring of flexibility and multi-functions. The design consists of three coplanar electrodes with dielectric layer(s) and light emission layer(s) coated on a top of input electrodes. It does not require transparent electrodes for electrical input and the light emission occurs when the top light-emitting layers are connected through a polar bridge. We demonstrate some applications of our three-phase electric power driven electroluminescent devices to realize pixel units, interactive rewritable displays and optical-output sensors. Furthermore, we also demonstrate the applicability of three-phase electrical power source to drive organic light-emitting devices with red, green and blue-emitting pixels and have shown high luminance (up to 6601 cd/m2) and current efficiency (up to 16.2 cd/A) from fabricated three-phase organic light-emitting devices. This novel geometry and driving method for electroluminescent devices is scalable and can be utilized even in a wider range of other types of light-emitting devices and special units.


globally.
In terms of power generation, a three-phase generator of the same size produces higher power than a single-phase generator. In the case of a three-phase balanced load, the generator torque is constant, which is beneficial for operation of the generator. In terms of power consumption, a three-phase electric power easy generates a rotating magnetic field making a three-phase motor to rotate smoothly. Finally, in terms of transmission, the three-phase system uses fewer wires compared to the single-phase system and the ratio of a conductor material to capacity is halved by using TP system. Importantly, it can be verified in theory that when the electric transmitting system for loads of equal capacity is changed from single-phase system to three-phase system, the line loss can be reduced by 6 times (when the three-phase load reaches equilibrium), as described below.
Assume that the three-phase load reaches equilibrium, all conductive wires are the same and the resistance of a single conductive wire is R, the current values in a single-phase power transmitting system and in a three-phase four-wire transmitting system are denoted by Isingle and Ithree, respectively. When the total power of the load in a single-phase power transmitting system is equal to that in a three-phase power transmitting system, the relationship between Isingle and Ithree follows Supplementary eq. 1:

Isingle= 3Ithree
(Supplementary eq. 1) When the three phases are balanced, the current in the neutral line is zero. Therefore, the line loss (Wsingle) of two conductive wires in a single-phase power transmitting system is expressed by Supplementary eq. 2: Wsingle = 2·Isingle 2 ·R = 2·(3Ithree) 2 ·R = 18·Ithree 2 ·R (Supplementary eq. 2) where R is the resistance of a single conductive wire.
At the same time, the total line loss when using a three-phase four-wire transmitting system (Wthree) is described by Supplementary eq. 3: Therefore, the line losses in a single-phase power transmitting system are 6 times higher of that in a three-phase transmitting system.

Supplementary Note 2: Distribution of electric field intensity between the phosphor layer
and the dielectric layer.
The TPEL device can be simulated by a two-layer dielectric model under uniform electric field as shown in Supplementary Fig. 2 (a,b). The thickness, dielectric constant and electric field intensity of the phosphor layer are denoted as d1, ε1 and E1, respectively. Similarly, the thickness, dielectric S3 constant and electric field intensity of the dielectric layer are d2, ε2 and E2, respectively. In such two-layer dielectric model under uniform electric field, the relationship Supplementary eq. 4 is true and the total voltage U in the two-layer dielectric model can be expressed by Supplementary eq. 5: (Supplementary eq. 5) Therefore, the distribution of the electric field intensity between the phosphor layer and the dielectric layer can be easily deduced as a function of ε1, ε2 and d1, d2 (Supplementary eq. 6 and Supplementary eq. 7): (Supplementary eq. 6) (Supplementary eq. 7) In order to increase the electric field intensity in the phosphor layer, we need the dielectric layer to be thinner and/or with higher dielectric constant.

circuit.
Suppose the voltage applied to the capacitor as a function of time (t) follows the Supplementary eq. 8: (Supplementary eq. 8) Then, the current can be expressed by Supplementary eq. 9: (Supplementary eq. 9) Thus, the current in a capacitance only circuit is always 90 ° ahead of the voltage applied.
However, our measurements ( Fig. 2a)   As demonstrated for TPEL devices, the effect of AC frequency on the performance of devices is also significant. Therefore, we investigated the dependencies of frequency on luminance and current efficiency of TP-OLEDs (at a fixed voltage of 53 V) (Fig. 6g,h). For all TP-OLEDs, the luminance increased with a frequency, with saturation at high frequencies and approaching the maximum values at the frequencies above ca 2 kHz. No decrease in luminance was observed even at high frequencies of 10 kHz (in contrast to TPEL devices, Supplementary Fig. 6). The current efficiencies showed peak values around 500 -2000 Hz, with dropping the efficiency at higher frequencies. It should be noted that only for pixel formed TPEL devices we need an extra electrode connected to the PEN (protective neutral) line and unless stated otherwise, we used three-phase three-wire system to drive TPEL devices. c, Schematic diagram of impedance triangle. Here, R is the impedance introduced by resistive component, X c is the impedance introduced by capacitive component, Z is the total impedance and α indicates the angle of total impedance (that is the angle between the current and voltage in the circuit).

Supplementary Figure 4 | Simple TPEL devices with no substrate and ubiquitous electrodes. a,
Photographs and inserted schematic structure of TPEL devices fabricated using tinfoil as an electrode (with no additional substrate on the bottom). DI water and copper wire (left) or hydrogel (right) were used as a polar electrode bridge between the lines. A blade coating method was used in this case and we did not deliberately control the thickness of each layer. b, Flexibility of the tinfoil based TPEL unit in (a). c, Photograph and inserted schematic cartoon of fibrous TPEL devices fabricated using copper wire as an electrode. DI water was used as a polar bridge. We used a dip coating method in this case without deliberately controlling the thickness of each layer. and sandwich (c) electric system driven devices. d, Luminance performance comparison between the three driving systems using the same device, in which X axis represents the phase voltage for a three-phase system and voltmeter readings in (b) and (c) for single-phase and sandwich systems, respectively. e, Luminance performance comparison of the three driving systems versus the line voltage. For the three-phase electric system, the actual voltage between the two arbitrary electrodes is the line voltage. So, the X axis of the three-phase driving system was modified into the line voltage (multiplying the phase voltage by √3). For a single-phase driving system, the actual voltage between two electrodes is a phase voltage, so it was kept unchanged. For a sandwich driving system, we used a conductive tape connected to the polar bridge layer to build up the top electrode. The theoretical value of the voltage driven by a sandwich system should be about 1/2 of the voltage driven by a single-phase system under the same conditions, so the X axis of the sandwich driving system was modified by multiplying the phase voltage by 2 for proper comparison. Commercial bath gel was used to form the polar bridge in this part. Source data are provided as a Source Data file. Glass-ITO was used as substrate / electrodes, with a light emitting area of 3 × 2 cm. Commercial phosphor (GG65, Leuchtstoffwerk Breitungen GmbH) was used in the light-emitting layer. The current efficiency is increased with an increase of the frequency to ca. 500 -1000 Hz and then decreased.
Source data are provided as a Source Data file. Here we used DI water as polar bridge in each part, which are connected by copper wires. b,c, The photographs of three separate units placed into the beakers with DI water, each of them is connected to one single-phase AC supply of the three-phases electric power: (b) without copper electrode bridges between the units (no light emission), (c) copper wires are used as bridges (each unit emits the light from its phosphor layer). The phosphors used as emissive layers on (b,c) are GG65, GG14 and GG45 (purchased from Leuchtstoffwerk Breitungen GmbH) from the left to the right. PET-ITO was used as substrate / electrode.

Supplementary Figure 12 | Schematic diagram of TPEL panel (lollipop-type electrode is shown as an example).
The conductive ITO film on PET substrate was divided into three uniform parts and three separated electrodes are shown in the schematic diagram as green, red and blue. It should be noted that we used ITO as electrodes, so all three electrodes are transparent. Three different colors are used in the schematic diagram just to distinguish the different electrodes visually. A three-phase three-wire system was used to drive the TPEL panel. Three electrodes were connected to three different live wires, respectively. DI water, hydrogel, water-based fluorescent pen or graphite pencil can be used to provide ink (acting as a polar electrode bridge) to create arbitrary light emitting pattern. Thus, only ink-covered areas will emit the light.
Supplementary Figure 13 | Photographs of multi-functional TPEL panels using lollipop-type electrodes (schematic diagram of which is shown in Supplementary Fig. 12), applied to the simulated environment of (a) snow, (b) frozen rain, (c) dew, (d) extremely wet environment (heavy fog, relative humidity 100%), (e) rain and (f) ice accretion. TPEL panels respond strongly to all these extreme environments starting to emit the light from the phosphor and raise an optical alarm remotely.  Figure S20) . Luminance (a,b), current efficiency (c,d) and power efficiency (e,f) performance comparison between the three driving systems using the same device at fixed frequencies of 1 kHz (a,c,e) and 10 kHz (b,d,f). X axes represent the phase voltage for three-phase system and voltmeter readings for single-phase and sandwich systems (see Figure  20), respectively. Device structure: