Abstract
The performance of solar cells with dual n(+) emitter and p base contacts at the back side fabricated on industrial (cost effective) silicon solar cell material is investigated by means of circuit modelling. The model is based on dividing the structure into sections which are modelled as distributed circuit segments each consisting of a diode, a current source and appropriate segment series resistances. The parameters of the circuit elements are determined from one dimensional simulations using the device simulator PC-1D. The circuit analysis is carried out analytically and confirmed by computer simulations using the circuit simulator HSPICE. The effects of the cell thickness, surface recombination velocity and diffusion length are investigated. Finally, the back side n(+)/p area aspect ratio that optimally resolves the trade-off between maximum n(+) area and minimum series resistance is determined. It is shown that the efficiency of back emitter cells with a standard thickness is 1.5% smaller than that of front emitter cells. On the other hand, the back emitter cell appears to be a serious contender for silicon cells thinner than 50 mu m. The analysis demonstrates that the back emitter cell should have good bulk quality and good surface passivation. It is also shown that the optimum separation between the n and p back metal contact is as large as 1.5-1.8 mm. Moreover, it is shown that the best performance is obtained with minimum back emitter contact width, and with two extra emitter contact stripes added parallel to the central emitter contact.