Low Reverse Saturation Current Density of Amorphous Silicon Solar Cell Due to Reduced Thickness of Active Layer

One of the most important characteristic curves of a solar cell is its current density-voltage (J-V) curve under AM1.5G insolation. Solar cell can be considered as a semiconductor diode, so a diode equivalent model was used to estimate its parameters from the J-V curve by numerical simulation. Active layer plays an important role in operation of a solar cell. We investigated the effect thicknesses and defect densities (Nd) of the active layer on the J-V curve. When the active layer thickness was varied (for N d = 8×10 17 cm -3 ) from 800 nm to 100 nm, the reverse saturation current density (J o ) changed from 3.56×10 -5 A/cm2 to 9.62×10 -11 A/cm 2 and its ideality factor (n) changed from 5.28 to 2.02. For a reduced defect density (N d = 4×10 15 cm -3 ), the n remained within 1.45≤n≤1.92 for the same thickness range. A small increase in shunt resistance and almost no change in series resistance were observed in these cells. The low reverse saturation current density (J o = 9.62×10 -11 A/cm 2 ) and diode ideality factor (n = 2.02 or 1.45) were observed for amorphous silicon based solar cell with 100 nm thick active layer.