Patent ID: 8198530

Claim:
A tandem solar cell, comprising: at least two layers of solar cells, a first layer and a second layer stacked upon one another in a light incident direction, a photon filter arranged in between the first solar cell layer and the second solar cell layer, the photon filter comprising a reflecting cover ( 110 ) on a light incident side, means for focusing disposed underneath the reflective cover and a photon reflector ( 150 ) on a side opposite the light incident side, the first solar cell layer arranged with the photon filter on a side opposite to the light incident side, the photon filter arranged to reflect photons of certain energies (λ 2 ) back into the first solar cell layer, the photon filter arranged to be transparent to photons of other energies (λ 1 ) not arranged to be reflected, and these photons arranged to enter the second solar cell layer, wherein the photon filter focuses said photons of other energies (λ 1 ), and the said photons enter through small apertures embedded in the photon reflector ( 150 ) from the photon filter side opposite to the light incident side, said side opposite to the light incident side being a photon reflector ( 150 ).