Experimental study of flat light-scattering substrates in thin-film silicon solar cells

In this work, a novel type of substrate for thin-film silicon solar cells is studied. The substrate has the advantage of being physically flat to allow the growth of cells with excellent material quality while being optically rough for enhanced light trapping that leads to high short-circuit current density. The substrate is made of rough zinc oxide (ZnO) which is grown on a flat silver reflector. The ZnO is then covered with amorphous silicon and the stack is polished to expose the tips of the pyramidal ZnO surface. The ZnO embedded in the amorphous matrix provides the desirable scattering of light while the surface onto which the cell is deposited is flat and allows for the growth of good-quality material. We present results of ∼4 μm thick microcrystalline silicon solar cells prepared on such substrates with high open-circuit voltages of 520 mV. We also demonstrate a large relative efficiency gain of 10% compared to a state-of-the-art cell which is grown directly on an optimized textured substrate.