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 °C. Samples with aluminum on an a-Si:H(n) layer annealed at 180°C had a contact resistivity below 1 mΩcm 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.