OPTOELECTRONICS LETTERS Vol.17 No.10, 15 October 2021 Double co-host emitter based top emitting white organic light emitting diodes with enhanced brightness and ef- ficiency Neha Jain 1,2 *, Sujata Pandey 3 , Rajiv Kr. Singh 4 , and O. P. Sinha 5 1. Department of ECE, Amity School of Engineering and Technology, Amity University, UP, Noida, India 2. Department of EEE, Galgotia College of Engineering and Technology, Greater Noida, India 3. Department of ECE, Amity School of Engineering and Technology, Amity University, UP, Noida, India 4. CSIR- National Physical Laboratory, New Delhi, India 5. Amity Institute of Nanotechnology, Amity University UP, Noida, India 1 (Received 18 November 2020; Revised 11 February 2021) ©Tianjin University of Technology 2021 Novel and simplified bi-layer top-emitting white organic light emitting diodes (OLEDs) with dual co-host emitters have been simulated and analyzed. They consist of yellow-green emitting layer (EML) as electron transport layer (ETL) and blue EML as hole transport layer (HTL). Novelty of the device lies in simplification of tri-layer white OLED to a bi-layered device which is done by merging yellow-green EML with ETL and blue EML with HTL. The simulated devices show Commission Internationale de L’Eclairage (CIE) colour coordinates well within the emission range of white light. The results show that device A with 5,6,11,12-tetraphenylnaphthacene (rubrene) doped ETL has achieved the lowest luminance but longest excited state lifetime. Device D with tris-(8-hydroxyquinoline) aluminum: 4-(dicyanomethylene)-2-t-butyle-6-(1,1,7,7- tetra-methyljulolidyl-9-enyl)4H-pyran (Alq 3 : DCJTB) as ETL which emits yellow light and 2, 7-bis [N, N-bis (4-methoxy-phenyl) amino]-9, 9-spirobifluorene (MS-TPD): bis(2-methyl-8- quninolinato)-4-phenylphenolate alu-minium (BAlq) as HTL which is responsible for blue light emission is found to have best characteristics when compared to other simulated devices. It has a maximum luminance of 10 000 cd/m 2 and current efficiency of 15.25 cd/A, respectively, and CIE coordinates are at (0.329, 0.319). The device is found to be compatible to be used in solid state lighting applications because of the low driving voltage of the device. Document code: A Article ID: 1673-1905(2021)10-0581-5 DOI https://doi.org/10.1007/s11801-021-0183-6                                                               * E-mail: aceneha@gmail.com White organic light emitting diodes (OLEDs) is getting popular because of its tremendous performance in many applications, like full colour flat panel displays, solid state lighting, back light of liquid crystal displays, sub-pixels of organic light emitting diode display etc [1,2] . White OLEDs are getting attention because of its out- standing performance that includes high power conver- sion efficiency, light in weight, its mechanical flexibility, high power efficacy and many more [1] . To increase the power efficacy of white OLEDs, efficient phosphores- cent dyes are generally mixed together to get the desired emission colour [1,2] . The white emission from the OLEDs can be realized by different methods which includes the modelling of different structures. This includes (i) mix- ing of different colour dyes in a single emitting layer, (ii) using multiple emitting layers (EMLs) in a single device, (iii) single or multiple EML which composes of host and guest emitters, (iv) using a single colour emitting OLED along with down conversion layer (v) excimer/exciplex emission. Excimers are the combination of molecules or atoms that can be only formed and can exist in excited states. Exciplexes can act as both emitter and host for phosphorescent and fluorescent emitters. Out of these, mixing of different colour dyes can be categorized into two parts. They are tri-layer emitting layers and dual EMLs. Tri-layer emitting layers consist of primary red, green, and blue colour dyes, whereas dual emitting layers consists of mixing of complementary colours, such as blue and orange, yellow-green and blue etc [1-5] . Out of these two, tri-layer EML have the advantage that they have high luminance and colour rendering index (CRI). But it complicates the device structure because of the large number of emitting layers and hence obscures the fabrication process. In addition, guest emitters if used in the structure affect the CIE coordinates. When we com- pare the two methods (dual and tri-layer emitter struc- tures) in terms of CIE coordinates, dual EML structure is found stable with CIE coordinates and also easy fabrica- tion process as compared to the tri-layer EML structure. Because of the different aging rates of the emitters used