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The influence of the thickness of silicon solar cells has been investigated using neighbouring multicrystalline silicon wafers with thickness ranging from 150 to 325 μm. For silicon solar cell structures with a high minority‐carrier diffusion length one expects that Jsc would decrease as the wafer becomes thinner due to a shorter optical path length. It was found experimentally that Jsc is nearly independent of the thickness of the solar cell, even when the minority‐carrier diffusion length is about 300 μm. This indicates that the Al rear metallisation acts as a good back surface reflector. A decrease in Jsc is observed only if the wafer thickness becomes less than about 200 μm. The observed trend in Voc as a function of the wafer thickness has been explained with PC1D modelling by a minority‐carrier diffusion length in the Al‐oped BSF which is small in relation to the thickness of the BSF. This effectively increases the recombination velocity at the rear of the cell. We have shown that the efficiency of solar cells made with standard industrial processing is hardly reduced by reducing the wafer thickness. Solar cell efficiencies might be increased by better rear surface passivation. Copyright © 2002 John Wiley & Sons, Ltd.

a b s t r a c tSeveral industrial n-type Czochralski silicon ingots were analysed on wafer and cell levels with ECN's bifacial n-type solar cell process. In some of the ingots, the solar cell performance in the very top drop of about 1% absolute with respect to cell from the middle part of the ingot. These cells show typical ring shaped pattern. After receiving a post-process anneal treatment at 200 1C, the efficiency nearly completly recover. We demonstrated that the improvement is due to bulk lifetime enhancement. The recovery is stable in storage conditions, under illumination and high temperature treatments up to 600 1C. The same effect cannot be reproduced in p-type Cz silicon solar cells with similar ring shaped patterns. This indicates that the defects responsible for lifetime and efficiency degradation in wafers affected by ring patterns differ in n-type and p-type.

Current bottlenecks for industrialization of Al2O3 deposited by Atomic Layer Deposition (ALD) for crystalline silicon solar cell applications are low growth rate and stability of thin and uncapped layers during co-firing. First results on the performance of a high throughput ALD prototype , the Levitrack, are presented. Excellent passivation properties have been obtained after firing, for 12 nm thick films deposited on p-Cz (2.3 Ω.cm) with Seff <15cm/s (∆n=3x10 15 cm-3). These layers are compatible with solar cells that operate at a maximum open-circuit voltage of 720mV. Furthermore, we report on the passivation of 20nm uncapped aluminum oxide layers on the rear of ptype mc-Si bifacial cells. LBIC measurements unveiled excellent passivation properties on areas covered by 20nm of Al2O3 characterized by an IQE of 91% at 980nm. Remarkably, these lifetime and cell results were obtained without lengthy post-treatments like forming gas anneal.