Low Frequency and Low Temperature Behavior of Si, Solar Cell by AC Impedance Measurements

In this work, the DC measurements and AC measurements (impedance spectra) have been used to characteristic the Si-module solar cell 6×6 (36 cells), 3.8 V and 85 mA. From the I-V characteristics under dark conditions for different temperatures (300 - 350 K) and by using the ARREHENIUS diagrams defined by Ln(I)=f(1/T) v=const, we have obtained the barrier height ψ(eV), ideal factor A, and the reverse saturation current Io(μA) eV, 2.83 and 0.831 The AC measurement impedance [X(ω)=f(R(ω))] has been employed to measure the parameters of the Si- module solar cell such as: heterogeneity factor, β, DC resistance Rdc, the bulk resistance Rb, activation energy E (eV), donor density Nd (cm-3), and density states Ns (cm-2). The solar cell module was exposed to thermal stress within the range (300 - 350° K), the diagram of complex impedance in the dark, was obtained. This plot gives arcs of a semicircle, their centers lie below the real axis R(ω),corresponding to the appearance of the depression angle (θ≠0), which represents,β(β=2θπ) which is in good agreement with the Cole-Cole diagram. It is noted that,, increases with temperature. The intersection of the circle arcs from the right with x axis (i.e. at very low frequency) gives Rdc the intersection from the left gives Rb, of the sample (2.77KΩ)(i.e. at very high frequency). By using ARREHENIUS diagrams defined by Ln(f)=f(1/T), we have obtained the parameters E (eV), Nd (cm-3), and Ns (cm-2), which equal to 0.354 eV, 1.38×1013 cm-3 and 6.93×109 cm-2 respectively.