Plasma‐immersion ion implantation: A path to lower the annealing temperature of implanted boron emitters and simplify PERT solar cell processing

Abstract

AbstractIon implantation is a suitable and promising solution for the massive industrialization of boron doping, which is a crucial process step for most next‐generation solar cells based on crystalline silicon (c‐Si). However, the use of ion implantation for boron doping is limited by the high temperature (in the 1050°C range) of the subsequent activation anneal, which is essential to dissolve the boron clusters and reach a high‐emitter quality. In this work, we propose the use of plasma‐immersion ion implantation (PIII) from B2H6 gas precursor instead of the standard beamline ion implantation (BLII) technique to decrease this temperature down to 950°C. PIII and BLII boron emitters were compared with annealing temperatures ranging from 950°C to 1050°C. Contrary to BLII, no degradation of the emitter quality was observed with PIII implants annealed at 950°C along with a full activation of the dopants in the emitter. At 1000°C, emitter saturation current densities (J0e) below 21 fA/cm2 were obtained using the PIII technique regardless of the tested implantation doses for sheet resistances between 110 and 160 Ω/sq. After metallization steps, the metal/emitter contact resistances were assessed, indicating that these emitters were compatible with a conventional metallization by screen‐printing/firing. The PIII boron emitters' performances were further tested with their integration in n‐type passivated emitter rear totally diffused (PERT) solar cells fully doped by PIII. Promising results already show a conversion efficiency of 20.8% using a lower annealing temperature than with BLII and a reduced production cost.