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

摘要

We have developed a new technique to characterize the individual layers of highhyphen;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 quantumhyphen;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 twoponnGaAs solar cells with AlxGa1minus;xAs passivation, we determined minorityhyphen;carrier hole diffusion lengths of 1.0plusmn;0.2 and 0.2plusmn;0.05 mgr; in the Tehyphen;dopednlayers for first and second samples, respectively. We found lower limits for the minorityhyphen;carrier electron diffusion lengths in the topplayers of 2.0 mgr; in the carbonhyphen;doped first sample and 4.0 mgr; in the Mghyphen;doped second sample. We determined interface recombination velocities of 4.0plusmn;0.5 (105) cm/s at the carbonhyphen;dopedplayerrsquo;s interface with its Al0.45Ga0.55As passivation layer, and between 500 and 104cm/s for the Mghyphen;doped layerrsquo;s interface with its Al0.9Ga0.1As passivation layer. After stripping the AlxGa1minus;xAs layer away, we measured surface recombination velocities of 8.0plusmn;2.0 (106) cm/s on the carbonhyphen;doped sample, and 1.0plusmn;0.2 (107) cm/s on the Mghyphen;doped sample.