Investigation of Rear Localized Back Surface Field Formed from Boron Laser Doping and Screen-printed Aluminum Paste in High-Efficiency Solar Cells

A localized back surface field (LBSF) cell was developed using boron laser doping (LD) and screen-printed aluminum paste firing to produce p-type passivated emitter, rear locally diffused cells with the objective of further enhancing the efficiency of the cell. After LD, the B dopant depth was over 6.0 μm and the B surface concentration was 1 × 1019 atoms/cm3. The Al paste was screen-printed and fired to form electrodes, and the LBSF composed of Al and B was observed using scanning capacitance microscopy. Secondary ion mass spectrometry was used to detect the B dopant in the LBSF area after firing the Al paste to clarify the reason for the improvement in the performance of the cell, and the ratio of B/Al was determined to be more than 0.9 wt%. The LBSF cell had an efficiency of 19.5%, which exceeded that of the reference cell by ∼1.1%, and the open circuit voltage of the cell improved remarkably. This indicated that the B content resulting from LD influenced Al diffusion and enhanced the LBSF effect.