Scanning light spot analysis of faulty solar cells

Laser scanning measurements on solar cell test pattern NBS-22

“…The application of the laser scanner to the study of solar cells initiated by Sawyer [1][2][3][4] at the National Bureau of Standards (NBS) has continued in a program to quantify its measurement potential and to evaluate its use in the detection of specific cell defects. The principal thrust of this report is to describe experimental verification of the theoretical photoresponse curves predicted by Lehovec and Fedotowsky [5] of the University of Southern California.…”

“…In order to provide the reader with a more nearly self-contained report, the results of previous work which were used in the measurements reported here are briefly described. They are 1) the solar cell test pattern [4] on which the measurements are made and 2) the theoretical results of Sawyer [3] and of Lehovec and Fedotowsky [5] on which the analysis is based.…”

“…An analysis of the photoresponse of a solar cell to a line of light parallel to a metallization line while the cell is uniformly forward biased by background illumination was made by Sawyer and Kessler [3] and extended to a spot of light by Lehovec and Fedotowsky [5] .…”

“…With the identification of g in eq ( 1 ) as the inverse of the attenuation length, the two expressions (1) and (5) become equivalent. It should be noted that the dependence of the photocurrent collected on the position of the laser spot is solely in the numerator of each egression.…”

“…The photoresponse of a cell containing a step change in sheet resistance, as introduced in cells C and D of figure 1, was calculated numerically by Lehovec and Fedotowsky [5] assuming that this is the only parameter that has changed in this portion of the solar cell. The lower doping concentration results in a higher sheet resistance which produces slightly greater curvature in the center region as seen in figure 5 for a sheet resistances of 45 fl/O in the center region and 31 fl/O in the side regions next to the metallization.…”