Selective tunnel oxide passivated contact on the emitter of large-size n-type TOPCon bifacial solar cells

This paper reports the application of novel selective tunneling oxide passivated contacts (TOPCon) on the emitter of large-Size n-type TOPCon bifacial solar cells. TOPCon technology is applied to the front surface of n-type TOPCon bifacial cells. The design of the front surface cell TOPCon layer was optimized, and only the SiO2/poly Si passivation layer was applied to metal contact of the emitter in order to avoid parasitic absorption of sunlight by the polysilicon layer. The quasi-steady state photo-conductance (QSSPC) analysis focused on the front-surface conventional n-type PERT cell structure and the front-surface selective TOPCon cell structure, resulting in a saturation current density of 1400 fA/cm2 for the front-surface metal contact recombination of the conventional n-type passivated emitter rear totally-diffused （PERT） cell structure and a saturation current density of 430 fA/cm2 for the front-surface metal contact recombination of the selective TOPCon cell structure. The maximum conversion efficiency of bifacial solar cells with a large area of 252 cm2 prepared using this technique reaches up to 23.21%. This represents an average conversion efficiency improvement of 0.21% compared to solar cells with a conventional PERT structure on the front surface and a TOPCon on the rear surface. Simulation of a cell optimized for this structure can achieve an open circuit voltage of over 720 mV, a short circuit current of 40 mA/cm2, and a cell efficiency of 24%.