GaAs/Si tandems for next generation high efficiency solar cells

This paper argues that GaAs/Si tandem solar cells are the most promising approach for next generation PV for reasons of efficiency and long-term performance stability. Although low-cost mass production of GaAs cells has not been established, a similar manufacturing challenge with single crystal Si has been solved. The theoretical limiting efficiency of GaAs/Si depends on device configuration, number of electrical terminals and layer thicknesses, and exceeds 40%. Current matching in the tandem sub-cells is difficult to achieve in practice and is not needed with 4-terminal electrical connections. Calculated limits and many years of experience with single crystal Si suggest that a GaAs/Si module efficiency of 35% is achievable. The extra efficiency available with tandems is particularly beneficial in residential applications where the balance of systems costs are high and space is constrained.