Modelling of the influence of dislocations on effective diffusion length and photocurrent of polycrystalline silicon cells

Green´s function is used to establish a three-dimensional model to obtain a detailed rigorous analytical expression of the effect of dislocations. The predictions of the model were verified by measuring the photocurrent, the spectral response, and the effective diffusion lengths of minority carriers (L_eff) and by evaluating the dislocation etch pit density. Three materials are considered, POLYX, SILSO, and SEMIX, which differ by the value of the diffusion length (L_n) in the homogeneous regions of the bulk. It is found that the values of J_sc and L_eff are dependent on N_dis and S_d provided they are greater than 10⁴ cm^-2 and 10⁴ cm-s^-1, respectively. The computed variations also depend on the value of the diffusion length in the homogeneous region of the bulk material. A reasonable agreement is found with experimental results obtained with large-grained polycrystalline materials such as SILSO and POLYX.