Development of a Conductive Distributed Bragg Reflector for Heterojunction Solar Cells Using N -Doped Microcrystalline Silicon and Aluminum-Doped Zinc Oxide Films

We report on the feasibility of integrating two conductive thin-film materials-n-doped hydrogenated microcrystalline silicon μc-Si:H(n) and Al-doped zinc oxide ZnO:Al-to form a conductive distributed Bragg reflector (DBR) at the rear of a silicon heterojunction solar cell, which simultaneously possesses high electrical conductance and high optical reflectance in the 900 ± 200 nm wavelength range. An optimization of the DBR is undertaken, considering the parasitic absorption in the thin films. Although an increased absorption loss is observed using the thicker films proposed by the DBR optimization, a significant increase in internal rear reflectance will compensate for this effect. If a full-area rear metal contact is used, in combination with a single DBR unit block, the rear´s sheet resistance decreases from 100 to 40 Ω/□, and the weighted average reflection from 700 to 1100 nm increases from 79.5% to 88.2% as compared with the nonoptimized thicknesses for the conductive films.