Optimization of self-doping Ag paste firing to achieve high fill factors on screen-printed silicon solar cells with a 100 Ω/sq. emitter

Self-aligned selective-emitter cells have been fabricated using a self-doping paste by co-firing the front and back contacts. Good ohmic contacts with ∼0.774 fill factor were obtained on 100 Ω/sq. emitters after alloying the self-doping Ag grid by a 900°C spike firing in a belt furnace. Screen-printed selective emitter Fz Si cells gave an efficiency of 16.4%. Selective-emitter cells with effective front-surface passivation produced almost 0.4% higher absolute efficiency than the conventional 45 Ω/sq. homogeneous-emitter cell co-fired at 850°C. IQE data showed a 23% higher spectral response at 400 μm wavelength for the passivated selective-emitter cell over the conventional 40-45 Ω/sq. emitter cell. This is due to lower front-surface recombination velocity and reduced heavy doping effects. Long-wavelength response of the selective-emitter cell was also slightly superior due to the improved back-surface field. As a result, the selective-emitter cell shows a much higher J_sc and V_oc than a cofired conventional-emitter cell. Rapid firing of the self-doping paste was found to be more effective than the slow firing process.