Analysis of features of recombination mechanisms in silicon solar cells

Abstract

Investigated in this paper are theoretical and experimental spectral dependences of the short-circuit current as well as small-signal photo-e.m.f. in silicon solar cells. The authors have considered two constructions of solar cells. The first construction is a solar cell with contacts on the front and back surfaces, and the second – solar cells with back barriers and contact metallization. Analyzed in the work are spectral dependences of the internal quantum efficiency for the short-circuit current and smallsignal photo-e.m.f. It has been shown that the short-wave drop of the short-circuit current is related with recombination on deep centers at the front surface as well as inter-band Auger recombination in the heavily doped emitter. At the same time, availability of the shortwave drop in the small-signal photo-e.m.f. is related with limitation of the efficient rate of surface recombination Seff(l) due to diffusion inflow. The latter takes place when a layer with the thickness dp and increased recombination is available near illuminated surface. In this case, the mechanism providing decrease in the small-signal photo-e.m.f. in the area of strong light absorption is related with increasing the efficient rate of surface recombination near the front surface, when the dominant amount of electro-hole pairs is generated in the layer with the increased recombination rate. The same mechanism is responsible for the short-circuit current drop in solar cells with back barriers and contact metallization. Juxtaposition of theoretical and experimental results enabled to determine parameters that characterize sub-surface properties of solar cells, namely: the thickness of the surface layer with increased recombination, lifetime of carriers in it, and dependences Seff(l).