Effect of high-temperature annealing on ion-implanted silicon solar cells

P-type and n-type wafers were implanted with phosphorus and boron, respectively, for emitter formation and were annealed subsequently at 950∼1050°C for 30∼90min for activation. Boron emitters were activated at 1000°C or higher, while phosphorus emitters were activated at 950°C. QSSPC measurements show that the implied V_oc of boron emitters increases about 15mV and the J₀₁ decreases by deep junction annealing even after the activation due to the reduced recombination in the emitter. However, for phosphorus emitters the implied V_oc decreases from 622mV to 560mV and the J₀₁ increases with deep junction annealing. This is due to the abrupt decrease in the bulk lifetime of the p-type wafer itself from 178μs to 14μs. PC1D simulation based on these results shows that, for p-type implanted solar cells, increasing the annealing temperature and time abruptly decreases the efficiency (Δη _abs =-1.3%), while, for n-type implanted solar cells, deep junction annealing increases the efficiency and V_oc, especially (Δη_abs =+0.4%) for backside emitter solar cells.