Properties And Imaging Of Thick Doped Amorphous Silicon In Direct Contact With Aluminum For Use In Silicon Heterojunction Solar Cells

We present the characterization of amorphous silicon/aluminum carrier-selective contacts in both front- and rear-emitter configurations, where the aluminum makes direct contact with the doped a-Si: H layers in silicon heterojunction solar cells. The resistance and passivation quality of these contacts have been measured using the transmission line measurement and the quasi-steady-state photoconductance techniques, respectively. The thickness of the doped a-Si: H layer in direct contact with the aluminum is 20 nm and post-aluminumsputtering annealing temperature ranges from 150-240 degrees C. Samples with aluminum on an a-Si: H(n) layer annealed at 180 degrees C had a contact resistivity below 1 m Omega cm(2) while the lifetime remained at 4.8 milliseconds-essentially unchanged from the pre-sputtered, passivated sample. These values are superior to those for the traditional silicon heterojunction contact with a transparent conductive oxide layer and can enable devices with low resistive losses and tremendous optical properties through the insertion of a low-refractive index dielectric material at a wellchosen contact fraction.