Performance of organic light-emitting devices using spin-dependent processes

Abstract

The maximum luminous efficiency of organic light-emitting materials is increased through spin-dependent processing. The technique is applicable to all electro-luminescent processes in which light is produced by singlet exciton decay, and all devices which use such effects, including LEDs, super-radiant devices, amplified stimulated emission devices, lasers, other optical microcavity devices, electrically pumped optical amplifiers, and phosphorescence (Ph) based light emitting devices. In preferred embodiments, the emissive material is doped with an impurity, or otherwise modified, to increase the spin-lattice relaxation rate (i.e., decrease the spin-lattice time), and hence raise the efficiency of the device. The material may be a polymer, oligomer, small molecule, single crystal, molecular crystal, or fullerene. The impurity is preferably a magnetic or paramagnetic substance. The invention is applicable to IR, UV, and other electromagnetic radiation generation and is thus not limited to the visible region of the spectrum. The methods of the invention may also be combined with other techniques used to improve device performance.

We claim:  
     
         1 . A method of increasing the efficiency of a luminescent material having current carriers with a spin flip rate, an emissive singlet recombination channel, and a non-emissive triplet recombination channel, and wherein the singlet recombination cross section is greater than the triplet recombination cross section, the method comprising: 
 processing the luminescent material so as to increase the spin flip rate of the current carriers.    
     
     
         2 . The method of  claim 1 , wherein the processing includes adding an impurity to the luminescent material.  
     
     
         3 . The method of  claim 1 , wherein the processing includes a magnetic field.  
     
     
         4 . The method of  claim 1 , wherein the processing includes an increase in effective spin temperature.  
     
     
         5 . The method of  claim 1 , wherein the material is a polymer.  
     
     
         6 . The method of  claim 1 , wherein the material is an oligomer  
     
     
         7 . The method of  claim 1 , wherein the material is a molecular crystal.  
     
     
         8 . The method of  claim 1 , wherein the material is a fullerene.  
     
     
         9 . The method of  claim 1 , wherein the impurity is magnetically active.  
     
     
         10 . The method of  claim 1 , wherein the impurity is a paramagnetic.  
     
     
         11 . The method of  claim 1 , wherein the impurity facilitates low-frequency vibrations.  
     
     
         12 . A light-emitting device incorporating the material of  claim 1 .  
     
     
         13 . A method of improving the efficiency of an organic light-emitting material having carriers which exhibit a spin-lattice relaxation rate, the method comprising: 
 adding an impurity to the material so as to increase the spin-lattice relaxation rate of the carriers.    
     
     
         14 . The method of  claim 13 , wherein the material is a polymer.  
     
     
         15 . The method of  claim 13 , wherein the material is an oligomer.  
     
     
         16 . The method of  claim 13 , wherein the material is a molecular crystal.  
     
     
         17 . The method of  claim 13 , wherein the material is a fullerene.  
     
     
         18 . The method of  claim 13 , wherein the impurity is magnetically active.  
     
     
         19 . The method of  claim 13 , wherein the impurity is a paramagnetic.  
     
     
         20 . The method of  claim 13 , wherein the impurity facilitates low-frequency vibrations.  
     
     
         21 . A light-emitting device incorporating the material of  claim 13 .  
     
     
         22 . An material for use in a high-efficiency light-emitting device, the material comprising: 
 an electro-luminescent compound in which useful light emission occurs only through the recombination of singlet excitons; and    an impurity, added so as to increase the spin flip rate of carriers propagating through the material.    
     
     
         23 . An electro-luminescent device, comprising: 
 a first electrode;    an electro-luminescent layer supporting the flow of current carriers having a spin-flip rate;    a second electrode; and    an organic electro-luminescent material and an impurity added the electro-luminescent layer so as to increase the spin flip rate of the current carriers.    
     
     
         24 . A laser, comprising: 
 a light-emissive layer from which light is emitted through the injection of current carriers having a spin-flip rate;    an optical resonator;    an organic electro-luminescent material and an impurity added to the light-emissive layer so as to increase the spin flip rate of the current carriers.