TCAD simulation of germanium-based heterostructure solar cell employing molybdenum oxide as a hole-selective layer

Abstract

Molybdenum Oxide (MoOx) has been used as a hole-extraction film for photovoltaic (PV) applications; however, its interaction with Germanium (Ge)-based solar cells is less understood. For the first time, this paper aims to physically model the Ge solar cell that incorporates MoOx for hole transportation at the front side of the PV device facing the sunlight. However, the charge transportation process within the PV device is influenced by several design parameters that need optimization. A higher work function of MoOx increases the barrier height against minority carriers of electrons which is beneficial for extricating holes at the front interface of MoOx/Ge. A progressive reduction in the recombination of charge carriers has been observed by including a passivation layer of amorphous silicon (i-a-Si:H). Similarly, inserting a passivation and back surface field (BSF) stack of i-a-Si:H strengthens the electric field and likewise reduces the recombination at the rear side of the device. An enhanced doping concentration of BSF assists in the favorable alignment of energy bands for improved charge transportation within the solar cell as the rear passivation maintains the field strength for accelerated movement of charge carriers. However, optimizing the thickness of the front-passivation film is challenging due to the parasitic absorption of light at larger thicknesses. A comparative study with the reference device revealed that the proposed device exhibited a step-increase in the conversion efficiency (η) from 4.23% to 13.10%, with a higher Jsc of 46.4 mA cm−2, Voc of 383 mV, and FF of 74%. The proposed study is anticipated to meet the research gap in the physical device modelling of Ge-based solar cells employing high work function MoOx as a carrier-selective layer that could be conducive to the development of highly efficient multijunction solar cells.