Investigation of the Effect of Resistivity and Thickness on the Performance of Cast Multicrystalline Silicon Solar Cells

Abstract

A low resistivity of 0.2-0.3 Omegacm has been shown to be optimum for high quality single crystal silicon for solar cells. However, for lower quality cast mc-Si, this optimum resistivity increases owing to a dopant-defect interaction, which reduces the bulk lifetime at lower resistivities. In this study, solar cells fabricated on 225 mum thick cast multicrystalline silicon wafers showed very little or no enhancement in efficiency with the decrease in resistivity. However, Voc enhancement was observed for the lower resistivity cells despite significantly lower bulk lifetimes compared to higher resistivity cells. After gettering (during P diffusion) and hydrogenation (from SiNx) steps used in cell fabrication, the bulk lifetime in 225 mum thick wafers from the middle of the ingot decreased from 253 mus to 135 mus when the resistivity was lowered from 1.5 Omegacm to 0.6 Omegacm. This paper shows that solar cells fabricated on 175 mum thick, 1.5 Omegacm, wafers showed no appreciable loss in the cell performance when compared to the 225 mum thick cells, consistent with PC1D modeling