Defect study in amorphous silicon/crystalline silicon solar cells by thermally stimulated capacitance

Interface traps created by amorphous silicon (a-Si) deposition using dc magnetron sputtering or a microwave plasma-enhanced chemical vapor deposition method onto p-type crystalline silicon (c-Si) substrates in solar cell structures were studied by thermally stimulated capacitance. The trap properties (type, energy, and concentration) have been estimated as a function of various cell fabrication conditions. Plasma deposition of a-Si is seen to induce electron traps when the c-Si substrates are pretreated with hydrofluoric acid, and hole traps when a thin oxide layer is initially present on the c-Si. A strong correlation is observed between the trap activation energies when electron trapping centers are present and the corresponding photoresponse of these solar cells. Solar cells with 10% efficiency fabricated by a-Si sputtered at 64 W of power, exhibit 3 × 10¹⁴ cm^-3 trapping centers with an activation energy of 0.44 eV.