Passivation property of ultrathin SiOx:H / a-Si:H stack layers for solar cell applications

A stacked layer of ultrathin hydrogenated silicon oxide (SiOx:H) and hydrogenated amorphous silicon (a-Si:H) has been developed to passivate the crystalline silicon (c-Si) surface (see graphical abstract). Silicon oxide has the advantage of excellent optical and passivation properties. The SiOx:H layer is deposited on the c-Si surface by atomic layer deposition (ALD), with its thickness precisely controlled below 2 nm. The a-Si:H layer is deposited on the SiOx:H layer by plasma-enhanced chemical vapor deposition (PECVD) with a specific doping property, i.e. intrinsic, n- or p-type. The samples are then annealed in the range of 100 degrees C to 950 degrees C to study the fundamental passivation properties. We find that a combination of an ultrathin SiOx:H and (p) a-Si:H layers shows a favorable passivation compared to a neat (p) a-Si:H layer. The effective minority carrier lifetime, measured by quasi steady-state photoconductance (QSSPC), is similar to 0.5 ms after low temperature annealing at 300 degrees C. The passivation property is discussed in terms of hydrogen concentration, bond configurations, stoichiometry x of SiOx:H, and material microstructure, characterized by Fourier transform infra-red (FTIR) and Raman spectroscopy. It is suggested that a reorganization of both the SiOx:H, and the (p) a-Si:H layers, associated with hydrogen diffusion, plays an important role in improving the passivation.