Increased efficiencies on CdTe solar cells via luminescence down-shifting with excitation energy transfer between dyes

The external quantum efficiencies of CdTe solar cells fabricated by the atmospheric pressure metal organic chemical vapour deposition (AP-MOCVD) method have been measured with one and two dye doped luminescence down-shifting (LDS) layers on top. Excitation energy transfer between the dyes is used to extend the absorption ability of the LDS layer to λ=350 nm and increase the external quantum efficiency (EQE) of the cells for wavelengths λ<540 nm. The observed increase in the EQE corresponds to a rise in the short circuit current density of 1.88 mA/cm2 under AM1.5G illumination spectra, which is equivalent to a 10% relative solar cell efficiency increase. A simple model is presented, which accounts for the absorption and photon collection efficiencies of the LDS layer.