this is a 39 down emitting oled structure 0023 fig2 is the energy level diagram 200 of the conventional organic stack shown in fig1 in equilibrium condition if a voltage is applied to the stack the band bending takes place and that is not shown in fig2 the lumo lowest unoccupied molecular orbital levels are shown as top horizontal steps 21 for various materials of the stack and the homo highest occupied molecular orbital are shown as bottom horizontal steps 22 for various materials of the stack the vacuum level is the top most stair case structure electron transport takes place at lumo levels and hole transport takes place at homo levels there is a barrier for electrons as could be seen from the step in lumo levels between the cathode 23 and electron transport layer 28 a similar barrier for electrons exists between the lumo levels of host layer 27 and hole transport layer 26 in the same way there is a barrier for holes that exists between the homo levels of anode 24 and hole injection layer 25 holes also face a barrier between hole injection layer 25 and hole transport layer 26 and again between hole transport layer 26 and the host layer 27 it can be noted that there is no barrier for holes between host layer 27 and the electron transport layer 28 like the one that exists for electrons between host layer 27 and hole transport layer 26 under the action of the electric field substantial number of holes can leak through the host layer because of the absence of any barrier and thus not take part in useful recombination with electrons 0024 fig3 is the cross section of thin film organic stack 300 of prior art which has an additional layer.