Design and application of ion-implanted polySi passivating contacts for interdigitated back contact c-Si solar cells

Ion-implanted passivating contacts based on poly-crystalline silicon (polySi) are enabled by tunneling oxide, optimized, and used to fabricate interdigitated back contact (IBC) solar cells. Both n-type (phosphorous doped) and p-type (boron doped) passivating contacts are fabricated by ion-implantation of intrinsic polySi layers deposited via low-pressure chemical vapor deposition and subsequently annealed. The impact of doping profile on the passivation quality of the polySi doped contacts is studied for both polarities. It was found that an excellent surface passivation could be obtained by confining as much as possible the implanted-and-activated dopants within the polySi layers. The doping profile in the polySi was controlled by modifying the polySi thickness, the energy and dose of ion-implantation, and the temperature and time of annealing. An implied open-circuit voltage of 721mV for n-type and 692mV for p-type passivating contacts was achieved. Besides the high passivating quality, the developed passivating contacts exhibit reasonable high conductivity (Rshn-type = 95 Omega/square and Rshp-type = 120 Omega/square). An efficiency of 19.2% (V-oc = 673mV, J(sc) = 38.0mA/cm(2), FF = 75.2%, and pseudo-FF = 83.2%) was achieved on a front-textured IBC solar cell with polySi passivating contacts as both back surface field and emitter. By improving the front-side passivation, a V-OC of 696mV was also measured. (C) 2016 AIP Publishing LLC.