Silicon gettering: Some novel strategies for performance improvements of silicon solar cells

摘要

This paper reports the recent performance improvements in crystalline silicon solar cells. These have been achieved by a combination of two mechanisms. One is related to the solar cell design which consists of grooving silicon substrates to obtain a structure suitable to perform an efficient gettering process. The proposed structure consists of buried emitter contacts rear locally diffused. Chemical-vapour etching has been used in the process sequence both to realize buried contacts and opening periodic arrangement of small deep grooving holes, for local aluminum diffusion. The second consists to perform a gettering sequence by Rapid Thermal (RT) heat treatments of p-type silicon in an infrared furnace, in controlled silicon tetrachloride (SiCl4) and N2 gas atmosphere. The resulting silicon shows an increase of minority drift mobility determined by Hall Effect to reach 1417 cm2 V− 1 s− 1, and a decrease in resistivity over 40 μ m on both sides of silicon substrates. Moreover, Light Beam Induced Current (LBIC) investigations show an improvement of diffusion bulk lengths (L n) to ward 210 μ m as compared to silicon starting substrates.