Direct solar energy conversion to electricity by the photovoltaic effect is limited by the energy spectrum of the solar irradiation. It is therefore essential to minimize the energy losses associated with the mismatch between the photon energies and the active materials in the cell.

Third generation solar cells (dye-sensitized, organic, and polymer cell types) suffer from an additional fundamental difficulty. They are limited to thin layers of the photoactive materials. These limitations arise from the charge separation mechanism and from the charge transport resistance of the layers. Consequently, the optical density of these cells is lower than the optimum for efficient solar spectrum utilization.

We research a generic configuration of photovoltaic systems for efficient energy conver-sion over the whole solar spectrum. Our design involves elements that collect the incom-ing solar radiation and enforce spectral selective absorption of the radiation by a series of individual cells, each optimized for a different part of the solar spectrum. While splitting the solar radiation into different solar cells, illumination within our system does not suffer from either the need for current matching or the multiple reflection losses associated with presently known tandem and spectral splitting photovoltaic systems.

In third generation solar cells, the new design increases the optical path thus resulting in high effective optical density even with ultra-thin layers of the photoactive material. Consequently, a significantly larger fraction of the solar radiation can be used than is possible now.

Results of dye-sensitized and organic solar cells of the new design will be presented.