Multilayer emitter of molybdenum oxide/silver/molybdenum oxide thin films for silicon heterojunction solar cells: Device fabrication and electrical characterization

Abstract

In a simplified heterojunction crystalline silicon (c-Si) solar cell, a molybdenum oxide/silver/molybdenum oxide (MoOx/Ag/MoOx) stack has been investigated as an alternative to the well-known p-type amorphous silicon hydrogenated (a-Si: H) layer or a single layer of MoOx. The optical characteristics of the MoOx/Ag/MoOx multilayer were studied and found to have acceptable features for embedding on the solar cell's front side. Using a straightforward fabrication technique, thermal evaporation, a device structure composed of Al/Ag/MoOx/Ag/MoOx/n-Si/MoOx/Mg/Al has been fabricated. Impedance spectroscopy measurements were performed and Nyquist plots revealed single semicircles in the frequency range (102 Hz - 106 Hz) and at different temperatures, indicating the formation of a junction between MoOx/Ag/MoOx and n-Si substrate and the establishment of good Ohmic contacts for the front/rear electrodes. Moreover, capacitance-voltage characteristics were used to determine the temperature dependency of the built-in potential, doping concentration, and depletion width. The temperature-dependent current-voltage plots for the cell suggested that the predominant carrier transport mechanisms in the forward bias regime are trap-assisted tunneling at V> 0.35 V and e-h pair recombination at 0.35–0.75 V. For the reverse bias regime, carriers transport is dominated by the current generation in the space-charge region. Additionally, the photovoltaic performance of the solar cell was measured under illumination.