Numerical modeling of an amorphous-silicon-based p-i-n solar cell

A simulation program for amorphous-silicon-based p-i-n solar cells which allows for accurate calculation of single-junction or multijunction cell response under monochromatic or global AM1.5 illumination is discussed. The device model is based on a complete set of Poisson and current continuity equations describing the amorphous intrinsic and microcrystalline or amorphous n⁺ and p⁺ contacts. It predicts solar cell behavior with uniform and nonuniform optical (mobility) bandgaps, spatially dependent doping densities, and various layer thicknesses, as demonstrated by the very good agreement between the experimental and simulated current-voltage characteristics of single cells, with the bandgaps in the range of 1.75 to 1.47 eV. The material parameters used in the simulation have been obtained from experimental results reported in the literature. The possibility of obtaining higher efficiencies using novel cell designs has also been investigated. Calculations have been carried out on cell structures in which the bandgap of the intrinsic layer is profiled to help hole transport. The most efficient structure, also confirmed by recent experimental data, incorporates normal profiling throughout the bulk of the intrinsic layer with a thin graded buffer at the p⁺ -intrinsic junction