Electroabsorption measurements and built-in potentials in amorphous silicon p–i–n solar cells

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Abstract
We present a technique for using modulated electroabsorption measurements to determine the built‐in potential in semiconductor heterojunction devices. The technique exploits a simple relationship between the second‐harmonic electroabsorption signal and the capacitance of such devices. We apply this technique to hydrogenated amorphous silicon (a‐Si:H)‐based solar cells incorporating microcrystalline Si p+ layers. For one set of cells with a conventional plasma‐deposited intrinsic (i) layer we obtain a built‐in potential of 0.98±0.04 V; for cells with an i layer deposited using strong hydrogen dilution we obtain 1.25±0.04 V. We speculate that interface dipoles between the p+ and i layers significantly influence the built‐in potential.