[Show abstract][Hide abstract] ABSTRACT: Increasing the area of interdigitated back-contact (IBC) solar cells featuring a busbar contact geometry requires the use of longer fingers. The finger resistance will, thus, be increased if the thickness of the metallization is kept constant. In order to maintain a thin metallization, it is beneficial to increase the num-ber of busbars per contact. However, using more than one busbar for each polarity implies an asymmetric contact geometry. As a consequence, under operation, the busbars of the same polarity carry different currents. Due to voltage drops over unavoidable electrical resistances, this may lead to significant potential differ-ences between these busbars. Since current–voltage characteristics are usually measured using separate sense contacts for the voltage measurement, the position and number of these contacts may con-siderably affect the shape of the resulting current–voltage charac-teristic and, thus, the fill factor. By means of simulations with the circuit simulator LTSpice, we show that a permanent contacting with soldered tabs allows for a correct determination of the fill fac-tor. A chuck used for temporary contacting should feature at least one sense contact per busbar and pin contacting resistances below 30 mΩ in order to keep the fill factor error below 0.5% absolute. Index Terms—Current–voltage characteristics, fill factor, inter-digitated back-contact (IBC) solar cell.
[Show abstract][Hide abstract] ABSTRACT: We report in detail on the luminescence imaging setup developed within the last years in our laboratory. In this setup, the luminescence emission of silicon solar cells or silicon wafers is analyzed quantitatively. Charge carriers are excited electrically (electroluminescence) using a power supply for carrier injection or optically (photoluminescence) using a laser as illumination source. The luminescence emission arising from the radiative recombination of the stimulated charge carriers is measured spatially resolved using a camera. We give details of the various components including cameras, optical filters for electro- and photo-luminescence, the semiconductor laser and the four-quadrant power supply. We compare a silicon charged-coupled device (CCD) camera with a back-illuminated silicon CCD camera comprising an electron multiplier gain and a complementary metal oxide semiconductor indium gallium arsenide camera. For the detection of the luminescence emission of silicon we analyze the dominant noise sources along with the signal-to-noise ratio of all three cameras at different operation conditions.
Full-text · Article · Mar 2011 · The Review of scientific instruments
[Show abstract][Hide abstract] ABSTRACT: We report on calibration-free photoluminescence carrier lifetime imaging for the examination of crystalline silicon wafers. The photoluminescence measurements are performed using an indium gallium arsenide (InGaAs) camera. The carrier lifetime is determined from the time dependent luminescence emission for a modulated optical excitation. A ratio, including four photoluminescence images, acquired at different times during the modulated excitation, is calculated and found to depend only on the camera integration time and the effective carrier lifetime. Therefore, the carrier lifetime is unambiguously determined by this ratio without the knowledge of any additional wafer properties. The carrier lifetime is obtained locally by comparing the experimentally determined ratio with the simulated ratio for every image pixel. We demonstrate the applicability of the dynamic photoluminescence lifetime imaging technique to multicrystalline silicon wafers by comparison with microwave-detected photoconductance decay and quasi steady-state photoconductance decay measure-ments.