Impact of boron doping on electrical performance and efficiency of n-TOPCon solar cell

A big challenge to improve the conversion efficiency of n-type solar cell is the recombination and electrical contacting of boron (B)-doped emitters in n-TOPCon solar cells. This work investigates the emitter dark saturation current density under the passivation layer (J0e, passivated), the metallization-induced recombination current density under the metal contact (J0e, metal), and the I–V parameters, including short-circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) and efficiency (Eff) as functions of the peak concentration (Nmax) and junction depth of B-doped profile. We introduced the profile with the peak concentration of 1–1.5 × 1019 atoms/cm3 and a junction depth of 0.75–1.0 μm to improve the conversion efficiency of 23.4%. The results revealed that Jsc, implied Voc (iVoc) and the contact resistance (ρc) were negative correlated with the Nmax and junction depth. However, J0e, passivated had a positive correlation with the same. The results from ρc, J0e along with the I–V showed the junction depth of emitter doping profiles need to exceed the corroded depth of Ag/Al paste to get a low ρc, meanwhile, a low J0e should be ensured. The results suggested theB-selective emitters were developed with a low ρc and a low J0e. After optimizing B-selective emitters and passivation processes, we obtained industry-grade TOPCon cells with Eff, Voc, Jsc, and FF as high as 23.7%, 709 mV, 40.8 mA/cm2, and 82%, respectively. This optimized B-doped and simplified B-selective emitters processes can be commercially applied in photovoltaics.