Amorphous silicon enhanced metal-insulator-semiconductor contacts for silicon solar cells
Carrier recombination at the metal-semiconductor contacts has become a significant obstacle to the further advancement of high-efficiency diffused-junction silicon solar cells. This paper provides the proof-of-concept of a procedure to reduce contact recombination by means of enhanced metal-insulator-semiconductor (MIS) structures. Lightly diffused n(+) and p(+) surfaces are passivated with SiO2/a-Si:H and Al2O3/a-Si:H stacks, respectively, before the MIS contacts are formed by a thermally activated alloying process between the a-Si: H layer and an overlying aluminum film. Transmission/scanning transmission electron microscopy (TEM/STEM) and energy dispersive x-ray spectroscopy are used to ascertain the nature of the alloy. Idealized solar cell simulations reveal that MIS(n(+)) contacts, with SiO2 thicknesses of similar to 1.55 nm, achieve the best carrier-selectivity producing a contact resistivity rho(c) of similar to 3 m Omega cm(2) and a recombination current density J(0c) of similar to 40 fA/cm(2). These characteristics are shown to be stable at temperatures up to 350 degrees C. The MIS(p(+)) contacts fail to achieve equivalent results both in terms of thermal stability and contact characteristics but may still offer advantages over directly metallized contacts in terms of manufacturing simplicity. (C) 2014 AIP Publishing LLC.