Application of concentrating luminescent down-shifting structures to CdS/CdTe solar cells with poor short wavelength response

Abstract A method to exploit both the wavelength shifting and light concentrating properties of luminescent plates in order to increase the current output of CdS/CdTe solar cells has been investigated. The application of concentrating luminescent down-shifting structures onto CdS/CdTe solar cells in order to combine the benefits of light concentration and wavelength shifting properties of luminescent plates is proposed. This technique is particularly effective in CdS/CdTe solar cells with a poor short wavelength response. An increase in the current output of close to 10% was measured on application of concentrating luminescent down-shifting structures compared to nearly 5% without light concentration to such solar cells. Concentrating luminescent down-shifting structures containing multiple fluorescent species allowed the absorption ability of the device to be extended to a wider range of wavelengths. This combined with strong energy transfer that red-shifts photons to wavelengths with even better solar cell response is seen to result in increases greater than 20% in the short circuit current output of CdS/CdTe solar cells. A general analytical expression that models different methods of applying of luminescent plates to solar cells is proposed which describes the performance of concentrating luminescent down-shifting structures well and can be used to separate the contributions of luminescence and incident excitation photons on the current output. These expressions can also be used to estimate the transport and reflection losses in these devices.