Backside texturing by cusps to improve ir response of silicon solar cells and photodetectors

Abstract

The absorption coefficient of silicon for infrared light is very low and most solar cells absorb very little of the infrared light energy in sunlight. Very thick cells of crystalline silicon can be used to increase the absorption of infrared light energy but the cost of thick crystalline cells is prohibitive. The present invention relates to the use of less expensive microcrystalline silicon solar cells and the use of backside texturing with diffusive scattering to give a very large increase in the absorption of infrared light. Backside texturing comprises a plurality of cusped features providing diffusive scattering. Constructing the solar cell with a smooth front surface results in multiple internal reflections, light trapping, and a large enhancement of the absorption of infrared solar energy.

1 - 29 . (canceled) 
     
     
         30 . A semiconductor solar cell or photodetector having improved incident radiation absorption of visible and infrared light wavelengths, comprising:
 a silicon substrate having a first surface available to the incident radiation being textured to provide internal Lambertian diffusive reflective scattering at least of the infrared light wavelengths and having a second surface;   a first layer disposed at said first surface, said first layer being transparent to the visible light and infrared light wavelengths of the incident radiation; and   a reflecting layer disposed adjacent said second surface, whereby said infrared light wavelengths are returned by the reflecting layer toward said textured first surface and into said silicon substrate.   
     
     
         31 . The semiconductor solar cell or photodetector of  claim 30  wherein said first layer is antireflective to visible and infrared light of the incident radiation. 
     
     
         32 . The semiconductor solar cell or photodetector of  claim 30  wherein said silicon substrate further comprises single crystalline silicon or multi-crystalline silicon substrate having a thickness in a range of 5 micrometers to 500 micrometers. 
     
     
         33 . The semiconductor solar cell or photodetector of  claim 30  wherein said silicon substrate further comprises deposited microcrystalline silicon having a thickness in a range of 1 micrometers to 10 micrometers. 
     
     
         34 . The semiconductor solar cell or photodetector of  claim 30  wherein said silicon substrate further comprises deposited amorphous silicon having a thickness in a range of 1 micrometer to 10 micrometers. 
     
     
         35 . The semiconductor solar cell or photodetector of  claim 30  wherein said silicon substrate further comprises both deposited microcrystalline silicon and deposited amorphous silicon having a thickness in a range of 1 micrometer to 10 micrometers, arranged as one of either (a) an amorphous layer and then a microcrystalline layer and an amorphous layer, or (b) an amorphous layer and a microcrystalline layer. 
     
     
         36 . The semiconductor solar cell or photodetector of  claim 30  wherein said silicon substrate further comprises both deposited amorphous silicon having a thickness in a range of 1 micrometer to 10 micrometers, and multicrystalline silicon having a thickness in the range 5 micrometers to 500 micrometers. 
     
     
         37 . The semiconductor solar cell or photodetector of  claim 30  wherein said silicon substrate further comprises both deposited amorphous silicon having a thickness in a range of 1 micrometer to 10 micrometers, and crystalline silicon having a thickness in the range 5 micrometers to 500 micrometers. 
     
     
         38 . The semiconductor solar cell or photodetector of  claim 30  wherein said reflecting layer further comprises a metallic layer. 
     
     
         39 . The semiconductor solar cell or photodetector of  claim 30  wherein said reflecting layer further comprises a layer having a thickness in a range of 0.05 micrometers and 5.0 micrometers. 
     
     
         40 . A semiconductor solar cell or photodetector having improved incident radiation absorption of visible and infrared light wavelengths, comprising:
 a silicon substrate having a first surface available to the incident radiation being textured by cusped features to provide internal Lambertian diffusive reflective scattering at least of the infrared light wavelengths and having a second surface;   a first layer disposed at said first surface, said first layer being transparent to the visible light and infrared light wavelengths of the incident radiation;   a second layer disposed at said second surface, said second layer being transparent to the infrared light wavelengths of the incident radiation; and   a reflecting layer disposed at said second layer and spaced apart from said second surface by said second layer, whereby said infrared light wavelengths are returned through said second layer toward said textured first surface.   
     
     
         41 . The semiconductor solar cell or photodetector of  claim 40  wherein the first surface having a plurality of cusped features, each having a shape of an inverse Fourier transform of a Lorentzian intensity pattern and disposed with bases of said plurality of cusped features arranged away from said second surface, adapted to form a diffusive radiation forward scattering layer for infrared wavelengths of radiation. 
     
     
         42 . The semiconductor solar cell or photodetector of  claim 40  wherein said textured layer further comprises one of a regular array of cusped features and a random array of cusped features. 
     
     
         43 . The semiconductor solar cell or photodetector of  claim 40  wherein said first layer is antireflective to visible and infrared light of the incident radiation. 
     
     
         44 . The semiconductor solar cell or photodetector of  claim 40  wherein said silicon substrate second substantially planar surface returns infrared light wavelengths returned from said reflective layer through said silicon substrate. 
     
     
         45 . The semiconductor solar cell or photodetector of  claim 40  wherein said silicon substrate further comprises single crystalline silicon or multi-crystalline silicon substrate having a thickness in a range of 5 micrometers to 500 micrometers. 
     
     
         46 . The semiconductor solar cell or photodetector of  claim 40  wherein said silicon substrate further comprises deposited microcrystalline silicon having a thickness in a range of 1 micrometer to 10 micrometers. 
     
     
         47 . The semiconductor solar cell or photodetector of  claim 40  wherein said silicon substrate further comprises deposited amorphous silicon having a thickness in a range of 1 micrometer to 10 micrometers. 
     
     
         48 . The semiconductor solar cell or photodetector of  claim 40  wherein said silicon substrate further comprises both deposited microcrystalline silicon and deposited amorphous silicon having a thickness in a range of 1 micrometer to 10 micrometers, arranged as one of either (a) an amorphous layer and then a microcrystalline layer and an amorphous layer, or (b) an amorphous layer and a microcrystalline layer. 
     
     
         49 . The semiconductor solar cell or photodetector of  claim 40  wherein said silicon substrate further comprises both deposited amorphous silicon having a thickness in a range of 1 micrometer to 10 micrometers, and multicrystalline silicon having a thickness in the range 5 micrometers to 500 micrometers. 
     
     
         50 . The semiconductor solar cell or photodetector of  claim 40  wherein said silicon substrate further comprises both deposited amorphous silicon having a thickness in a range of 1 micrometer to 10 micrometers, and crystalline silicon having a thickness in the range 5 micrometers to 500 micrometers. 
     
     
         51 . The semiconductor solar cell or photodetector of  claim 40  wherein said reflecting layer further comprises a layer having a thickness in a range of 0.05 micrometers and 5.0 micrometers.