Abstract
In this work, we propose an analysis approach to determine the individual surface recombination velocities (S1 and S2) on each surface of an unequally passivated wafer, which precludes the crude assumption of S1=S2 in conventional methods. Taking advantage of the surface distributed excess charge carriers relatively sensitive to the surface recombination, we probe the sample using quasi-steady-state illumination of the xenon flash lamp equipped with a short pass filter (FSP1). A set of samples passivated by SiO2 and SiNx, as well as bare silicon wafers, are prepared in the experiment. On the basis of fitting the measured time-dependent-excess charge carriers, S1 and S2 are determined based on our analysis approach. The spatial and the temporal distributions of excess charge carrier density are presented. The dependence of τeff on the wavelength, S and τbulk is also discussed in detail. The reliability of this method is finally verified with a long pass filter (FLP2).
Highlights
In the industrial context of photovoltaics, the surface recombination velocity (S) is one of the most important parameters relevant to the solar cell design strategies and the process optimization.[1]S can not be directly obtained from measurements, and it is always in a combination with the bulk lifetime reflected by the minority carrier effective lifetime measured from lifetime measurements
Inspired by the modelling in Ref. 14, which described the possibility of using front and back illumination to discriminate between the front and rear surface recombination velocities of a solar cell, we experimentally demonstrate a method to determine the respective surface recombination velocities of a silicon wafer based on measurements of the photoconductance under the short wavelength illumination
This approach employs the QSSPC technique, using the xenon flash lamp equipped with a short wavelength filter (FSP1), to generate an asymmetrically distributed excess charge carriers throughout the wafer
Summary
S can not be directly obtained from measurements, and it is always in a combination with the bulk lifetime (τbulk) reflected by the minority carrier effective lifetime (τeff) measured from lifetime measurements. S is based on the simple approximation: 1 τeff =1 τbulk +. Where τeff, τbulk and W denote the effective lifetime, the bulk lifetime and the thickness of wafers, respectively.[5,6] it is assumed that the excess charge carrier density (∆n) is constant throughout the wafer and the sample must be very well passivated (S
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