Electron reflector strategy for CdTe solar cells

Incorporation of an electron reflector is a proposed strategy to improve V_oc for CdTe solar cells by reducing electron contact with the back surface. An electron reflector is a conduction band barrier, which can be formed by a back layer with an expanded band gap, a reversed back barrier, or a heavily doped back surface. These approaches to electron reflectors in CdTe solar cells are investigated with numerical simulations. The expanded band gap is shown to be the more efficient and practical way to create a CdTe electron reflector. For optimal improvement with an electron reflector, reasonable lifetime (1 ns or above) and full depletion are required. Without full depletion, bulk recombination limits the improvement. Theoretically, a 200 mV increase in voltage and 3% in efficiency are achievable for a 2-micron CdTe cell with 10¹³-cm^-3 hole density, 1-ns lifetime, and a 0.2-eV electron reflector barrier.