A new sequentially etched quantum-yield technique for measuring surface recombination velocity and diffusion lengths of solar cells

Abstract

We have developed a new technique to characterize the individual layers of high-efficiency solar cells. In general, the technique allows one to set lower bounds for diffusion lengths and upper and lower bounds for interface recombination velocity. This is sufficient to determine which parameter limits performance, and often the actual parameter values are also determined accurately. We obtain this information by fitting a theoretical model to quantum-yield spectra measured on a sample in its initial state, and after its window passivation and top active layers are sequentially etched away. With such data on two p on n GaAs solar cells with AlxGa1−xAs passivation, we determined minority-carrier hole diffusion lengths of 1.0±0.2 and 0.2±0.05 μ in the Te-doped n layers for first and second samples, respectively. We found lower limits for the minority-carrier electron diffusion lengths in the top p layers of 2.0 μ in the carbon-doped first sample and 4.0 μ in the Mg-doped second sample. We determined interface recombination velocities of 4.0±0.5 (105) cm/s at the carbon-doped p layer’s interface with its Al0.45Ga0.55As passivation layer, and between 500 and 104 cm/s for the Mg-doped layer’s interface with its Al0.9Ga0.1As passivation layer. After stripping the AlxGa1−xAs layer away, we measured surface recombination velocities of 8.0±2.0 (106) cm/s on the carbon-doped sample, and 1.0±0.2 (107) cm/s on the Mg-doped sample.