Defect Density Profiling in Light-Soaked and Annealed Hydrogenated Amorphous Silicon Solar Cells

ABSTRACTThe fundamental ingredient lacking in solar cell modeling is the spatial distribution of defects. To gain this information, we use drive-level capacitance profiling (DLCP) on hydrogenated amorphous silicon solar cells. We find the following: Near the p-i interface the defect density is high, decreasing rapidly into the interior, reaching low values in the central region of the cell, and rising rapidly again at the n-i interface. The states in the central region are neutral dangling-bond defects whose density agrees with those typically found in similar films. However, those near the interfaces with the doped layers are charged dangling bonds in agreement with the predictions of defect thermodynamics. We correlate the changes in solar cell efficiency owing to intense illumination with changes in the defect density throughout the cell. Defects in the central region of the cell increase to values typically found in companion films. We describe the measurements and interpretation of DLCP for solar cells with the aid of a solar cell simulation.