Optimization of Boron Spin on Dopant (BSoD) Diffusion for Emitter Formation in n-type c-Si Solar Cells

Abstract

Boron spin on dopant (BSoD) is an alternative boron source to BBr3 liquid dopant for p+ emitter formation in n-type solar cells. In this work, we have used different process control steps to lower the BSoD diffusion issues to have a uniform sheet resistance of p+ emitters. After eliminating the boron (B) precipitates formed during the process of diffusion by control process steps, the emitters have been optimized for sheet resistance values ≤60Ω/□ with variation less than ±5Ω/□. The corresponding junction depth is less than 800nm as measured by SIMS analysis. All the experiments are carried out with Czochralski n-type c-Si wafers which showed an improvement of effective minority carrier lifetimes by more than 2 times in controlled process steps. The measured Sun’s Voc and implied Voc are in the range 575- 600mV without any passivation. The PC1D simulation shows the efficiency of the solar cell without any passivation is 14.8%. This indicates the BSoD as a promising source for the p+ emitter formation in n- type c-Si solar cells.