Practical challenges of achieving high efficiency boron back surface field solar cells

This work examines two challenges facing the commercialization of boron diffused crystalline silicon solar cells - unintentional iron contamination and the passivation of a textured boron diffused surface. We find that when Fe is introduced into silicon wafers by boron diffusion, the Fe often remains trapped in the boron surface layer and undetectable using bulk lifetime measurements. However this trapped Fe is still a threat to bulk lifetime since subsequent thermal processes can inject this Fe into the bulk. Importantly, POCl₃ appears to be ineffective at gettering the trapped Fe; POCl₃ gettering works only when the trapped Fe is injected into the bulk prior to POCl₃ deposition. An alternate strategy is to directly getter the trapped Fe by using a negatively charged dielectric that is placed on the boron diffused surface. Random pyramid texturing was found to be detrimental to the spin-on SiO₂ induced passivation of a boron doped surface. This passivation loss can be minimized by removing the texture with a KOH etch and ~650 mV V_OC could be achieved on both FZ and Cz material.