Method and means for a high power solar cell

Abstract

In methods and apparatus for improving the power generated, and thus efficiency of solar cells, a double or triple junction tandem solar cell that has one or two photon filters of the invention in between the solar cell layers, respectively. The photon filter is arranged to reflect photons with wavelength shorter than λ x and arranged to be transparent to photons of wavelength longer than λ x by focussing the lower energy photons out of small area apertures on the other side of the photon filter and arranging the other side of the photon filter to reflect at least some of the photons of wavelength longer than λ x . By using the photon filters of the invention in between the solar cell layers, photons can be trapped between filters to solar cell layers at an energy at which the quantum efficiency of the solar cell layer is the best.

1 . A tandem solar cell, comprising at least two layers of solar cells, the first ( 200 ) and the second ( 201 ) layer,
 a first photon filter ( 100 ) is arranged in between the first solar cell layer ( 200 ) and the second solar cell layer ( 201 ),   the first solar cell layer ( 200 ) is arranged with the photon filter ( 100 ) on the side opposite to the incident side of sunlight,   the photon filter ( 100 ) is arranged to reflect photons of certain energy (λ 2 ) back into the first solar cell layer ( 200 ),   the photon filter ( 100 ) is arranged to be transparent to photons of other energies (λ 1 ) not arranged to be reflected, and these photons are arranged to enter the second solar cell layer ( 201 ), characterised in that,   
       photon filter ( 100 ) is arranged to reflect photons with wavelengths shorter than λ 2  from its first side ( 110 ,  111 ) and arranged to be transparent to photons of wavelengths longer than λ 2  by focussing ( 120 ,  121 ) the said longer wavelength photons out of small area apertures ( 140 ,  141 ) on the other side opposite to the first side ( 150 ,  151 ) of the photon filter ( 100 ,  101 ) and the other side of the photon filter ( 100 ,  101 ) is arranged to reflect ( 150 ,  151 ) at least some of the said photons of wavelength longer than λ 2 . 
     
     
         2 . A tandem solar cell as claimed in  claim 1 , characterised in that, the said certain energies (λ 2 ) are energies where the first solar cell layer ( 200 ) has higher quantum efficiency (QE) than the second solar cell layer ( 201 ), and/or the said other energies (λ 1 ) are energies where the second solar cell layer ( 201 ) has higher quantum efficiency (QE) than the first solar cell layer ( 200 ). 
     
     
         3 . A tandem solar cell as claimed in  claim 1 , characterised in that, the second solar cell ( 201 ) is arranged with a photon reflector on the side opposite to the incident side of sunlight ( 111 ) and on the sunlight incident side ( 150 ). 
     
     
         4 . A tandem solar cell as claimed in  claim 1 , characterised in that, the photon filter ( 100 ,  101 ) is arranged to focus ( 120 ,  121 ) the said photons of other energies, and the said photons enter through small apertures ( 140 ,  141 ) from the photon filter ( 100 ,  101 ) side opposite to the incident side of sunlight ( 150 ,  151 ). 
     
     
         5 . A tandem solar cell as claimed in  claim 1 , characterised in that, the photon filter ( 100 ,  101 ,  102 ,  103 ) is a dielectric stack and/or Rugate filter and/or a combination of both filters. 
     
     
         6 . A tandem solar cell as claimed in  claim 1 , characterised in that, the second solar cell layer ( 201 ) is arranged with a second photon filter ( 101 ) on the side opposite to the incident side of sunlight. 
     
     
         7 . A tandem solar cell as claimed in  claim 6 , characterised in that,
 the second photon filter ( 101 ) is arranged to reflect photons back into the second solar cell ( 201 ) with energies that are energies where the second solar cell layer ( 201 ) has a high quantum efficiency,   the first photon filter ( 100 ) is also arranged to reflect photons back into the second solar cell layer ( 201 ) with energies that are energies where the second solar cell layer ( 201 ) has a high quantum efficiency with a photon reflector ( 150 ) that is on the side opposite to the incident side of sunlight in the first photon filter ( 100 ),   the photon filters ( 100 ,  101 ) are arranged to entrap photons into the second solar cell layer ( 201 ) that are at energies where the second solar cell layer ( 201 ) has a high quantum efficiency (QE).   
     
     
         8 . A tandem solar cell as claimed in  claim 6 , characterised in that,
 the second photon filter ( 101 ) is arranged to be transparent to photons that are not at energies where the second solar cell ( 201 ) has a high quantum efficiency (QE),   the said transparent photons are arranged to enter a third solar cell ( 202 ).   
     
     
         9 . A method of producing the solar cell of  claim 1 . 
     
     
         10 . A tandem solar cell, comprising at least two solar cell layers, characterised in that, the said tandem solar ( 20 ,  30 ) cell is arranged to transport an incoming photon to a solar cell layer ( 200 ,  201 ,  202 ,  203 ) that has the highest quantum efficiency (QE) at the energy of the said incoming photon in comparison to the other said solar cell layers in the tandem solar cell. 
     
     
         11 . A tandem solar cell as claimed in  claim 6 , characterised in that, the said transported photons are arranged to be trapped into the said solar cell layer ( 200 ,  201 ,  202 ,  203 ) with the best quantum efficiency (QE). 
     
     
         12 . A tandem solar cell, comprising at least two layers of solar cells, the first ( 200 ) and the second ( 201 ) layer, characterised in that,
 a first photon filter ( 110 ) is arranged in between the first solar cell layer ( 200 ) and the second solar cell layer ( 201 ),   an antireflection layer ( 160 ,  165 ) is arranged between the said first photon filter ( 110 ) and the second solar cell layer ( 201 ),   a second photon filter ( 170 ) is arranged between the said antireflection coating ( 160 ) and the second solar cell layer ( 201 ).   
     
     
         13 . A tandem solar cell as claimed in  claim 12 , characterised in that, the antireflection layer ( 160 ,  165 ) is established by coarsening the surfaces in the interface between the first photon filter ( 110 ) and the second photon filter ( 170 ). 
     
     
         14 . A tandem solar cell as claimed in  claim 12 , characterised in that, the antireflection layer ( 160 ) is established with a quarter wavelength antireflection layer. 
     
     
         15 . A tandem solar cell as claimed in  claim 12 , characterised in that, photons are arranged to be trapped into the solar cell layer with the best relative quantum efficiency (QE). 
     
     
         16 . A tandem solar cell comprising at least two layers of solar cells, the first solar cell layer ( 200 ) and the second solar cell layer ( 201 ), characterised in that, at least one unidirectional photon filter ( 100 ) is arranged between the said first ( 200 ) and the second ( 201 ) solar cell layers. 
     
     
         17 . A tandem solar cell as claimed in  claim 16 , characterised in that, photons are arranged to be trapped into the solar cell layer ( 200 ,  201 ,  202 ,  203 ) with the best relative quantum efficiency (QE). 
     
     
         18 . A tandem solar cell comprising at least two layers of solar cells, the first solar cell layer ( 200 ) with a band gap energy of E bg  and the second solar cell layer ( 201 ), characterised in that, the second solar cell ( 201 ) has a lower refractive index than the first solar cell layer ( 200 ) at photon energies equal or higher than E bg . 
     
     
         19 . A tandem solar cell as claimed in  claim 18 , characterised in that, the second solar cell ( 201 ) has a higher refractive index than the first solar cell layer ( 200 ) at photon energies lower than E bg . 
     
     
         20 . A tandem solar cell comprising at least two layers of solar cells, the first solar cell layer ( 200 ) and the second solar cell layer ( 201 ), characterised in that, at least one solar cell layer ( 200 ,  201 ) is arranged to have its quantum efficiency (QE) vs. wavelength function and its refractive index vs. wavelength functions to reach peak and/or high values at the same wavelengths. 
     
     
         21 . A portable electronic device comprising at least one solar cell, characterised in that, said portable electronic device features at least one piezoelectric crystal and/or at least one mechanical means arranged to generate electricity from mechanical movement of said portable electronic device. 
     
     
         22 . A portable electronic device comprising at least one solar cell, said portable electronic device comprising at least one piezoelectric crystal and/or at least one mechanical means arranged to generate electricity from mechanical movement of said portable electronic device, characterised in that, the said solar cell is a tandem solar cell as claimed in  claim 1 .