Surface Passivation of CdTe Single Crystals

Low open-circuit voltages (850-870 mV), due to excessive bulk and surface recombination, currently limit CdTe photovoltaic efficiencies. Here, we study surface recombination in single crystals with single-photon excitation time-resolved photoluminescence (1PE-TRPL) to measure minority carrier lifetimes. Typically, minority carrier lifetimes of untreated undoped CdTe material as measured by 1PE-TRPL are ∼100 ps or less, even though their bulk lifetimes as measured by two-photon excitation TRPL can reach 100 ns. Such short 1PE-TRPL lifetimes indicate very high surface recombination velocities exceeding 100 000 cm/s. Here, we examine treatments that can reduce surface recombination and discuss different ways of evaluating their efficacy.