Influence of post deposition fabrication steps and quantitative estimation of band diagram of Si/MoOX heterojunction for carrier selective solar cells

Abstract

Heterojunction of molybdenum oxide with silicon is used as an effective hole collector in Si based carrier selective solar cells. Although the deposition of MoOX on Si is a low temperature process, the subsequent processes involved in the fabrication of the solar cell can impact the hole collection efficiency of Si/MoOX junction. In this manuscript we address the influence of post-deposition fabrication processes the subsequent processes involved in the fabrication of the solar cell can impact the hole collection efficiency of Si/MoOX junction. In this work we have found that the necessary annealing and sputtering steps have a degrading impact on the heterojunction. The underlying reasons are identified and widely described. Furthermore, to gain insight into the unique transport mechanism of heterojunction, a quantitative band diagram is obtained based on the empirical data (electron spectroscopy, optical and electrical measurements). The workfunction of thermally evaporated MoOX is found to be strongly substrate dependent and the electron affinity is deduced and measured to be 5.09 eV. The doping of MoOX films due to oxygen vacancies is found to be non-uniform as the oxygen content of the film decreases rapidly, from MoOX surface to Si/MoOX interface. Lastly, we report Si/MoOX heterojunction solar cells with high short circuit current of 33.9 mA/cm2, an open circuit voltage (VOC) of 585 mV, and an efficiency of 12.8%.