Broadband antireflection coatings under coverglass using ion gun assisted evaporation

Abstract

The present disclosure generally relates to broadband antireflective coatings for reducing reflection of light in the infrared without compromising visible light reflectance in multijunction solar cells bonded to coverglass, and methods of forming the same. The antireflective coatings include a high index, one or more intermediate index, and low index of refraction dielectric layers. The high index dielectric layer utilizes an ion beam assisted deposition to maximize the density and index of refraction. The intermediate index layer(s) increase the bandwidth of the antireflection coating, thereby improving the performance of the antireflective coating in the infrared spectrum.

1 . An antireflective coating, comprising:
 a first layer comprising a first material and having a first index of refraction within a range of about 2.3 to about 2.7, wherein the first material comprises titanium oxide;   an intermediate layer comprising the first material disposed on the first layer, the intermediate layer having an index of refraction and a density less than the first layer;   a second layer disposed on the intermediate layer, the second layer having an index of refraction less than the intermediate layer and within a range of about 1.8 to about 2.1; and   a third layer disposed on the second layer, the third layer having an index of refraction within a range of about 1.6 to about 1.8.   
     
     
         2 - 4 . (canceled) 
     
     
         5 . The antireflective coating of  claim 1 , wherein the titanium oxide is deposited using an ion beam-assisted deposition technique. 
     
     
         6 . The antireflective coating of  claim 5 , wherein the second layer comprises tantalum oxide. 
     
     
         7 . The antireflective coating of  claim 6 , wherein the third layer comprises aluminum oxide. 
     
     
         8 . The antireflective coating of  claim 1 , wherein the first layer has a thickness within a range of about 20 nanometers to about 60 nanometers. 
     
     
         9 . The antireflective coating of  claim 1 , wherein the second layer has a thickness of about 1 nanometer to about 50 nanometers. 
     
     
         10 . The antireflective coating of  claim 1 , wherein the third layer has a thickness within a range of about 50 nanometers to about 100 nanometers. 
     
     
         11 . A solar cell, comprising:
 a multijunction cell; and   an antireflective coating disposed on the multijunction cell, the antireflective coating comprising:
 a first layer comprising a first material and having a first index of refraction within a range of about 2.3 to about 2.7, wherein the first material comprises titanium oxide; 
 an intermediate layer comprising the first material disposed on the first layer, the intermediate layer having an index of refraction and a density less than the first layer; 
 a second layer disposed on the first layer, the second layer having an index of refraction within a range of about 1.8 to about 2.1; and 
 a third layer disposed on the second layer, the third layer having an index of refraction within a range of about 1.6 to about 1.8. 
   
     
     
         12 . The solar cell of  claim 11 , further comprising a glass coversheet and index matched adhesive disposed over the antireflective coating. 
     
     
         13 - 15 . (canceled) 
     
     
         16 . The antireflective coating of  claim 11 , wherein the second layer comprises tantalum oxide, and the third layer comprises aluminum oxide. 
     
     
         17 . The antireflective coating of  claim 11 , wherein the second layer comprises hafnium oxide, and the third layer comprises aluminum oxide. 
     
     
         18 - 20 . (canceled) 
     
     
         21 . The antireflective coating of  claim 1 , wherein the first layer has a first index of refraction between about 2.4 and about 2.5. 
     
     
         22 . The solar cell of  claim 11 , wherein the first layer has a first index of refraction between about 2.4 and about 2.5. 
     
     
         23 . The solar cell of  claim 11 , wherein the solar cell has an average reflectance of about 5 to about 5.5 percent in the infrared region.