Evaluation of molybdenum disulfide (MoS2) as the back layer for the silicon heterojunction solar cell (SHJ)

Abstract

Silicon heterojunction solar cells (SHJ) are one of the promising photovoltaic technologies due to their high efficiency, structural symmetric processibility, and low thermal coefficient. Despite SHJ advantages, free carrier absorption (FCA) and light reflection effects in the near-infrared (NIR) light spectrum demerits SHJ and are reportedly caused by the front and back SHJ's transparent conductive oxides (TCOs). Therefore, this dissertation endeavoured to evaluate Molybdenum disulfide (MoS2) as a back layer in an SHJ to reduce the TCOs NIR free carrier absorption effect (FCA). The simulated and optimized MoS2 thickness on SHJ using Sunsolve raytracing software demonstrated that 2D-MoS2 improves the SHJ's efficiency by about 0.004 % (rel.), which is insignificant. Conversely, a comparative study using Atlas-Silvaco software revealed a similar optical and electronic results trend. However, Atlas showed better electronic results than the Sunsolve model with the (2D)-MoS2 efficiency improvement difference of ~ 3.10% (rel.) over the reference SHJ, thanks to the wellsimulated electronic junctions. In collaborative works, the practical application of twodimensional (2D)-MoS2 underwent contact engineering through n-type doping using Dichloromethane as an n-doping agent, shifting the equilibrium state fermi level towards the conduction edge. In contrast, gold nanoparticles (AuNPs) were employed as a p-doping agent for MoS2. However, where the latter was effective doping, the required Schottky barrier lowering can be achieved only with the n-doping since MoS2 is on the backside of the SHJ solar cell. Furthermore, it offered a better charge carrier extraction lifetime and reduced the Schottky barrier compared with pristine MoS2. As a result of the increased Jsc due to the NIR light management and contact engineering, the power conversion efficiency (PCE) results for SHJ incorporated MoS2 (SHJ/MoS2) was improved from 11.45% to 13.03 %. External quantum efficiency (EQE) and reflectance results suggest MoS2 constructive NIR light interference with back layers improved light current density (Jsc). Overall, the experimental results consented to the simulation results, possibly due to the actual Schottky height barrier lowering. This suggests that the 2D Transition Metal Dichalcogenides (TMDC) materials may have a potential for solar cell applications with effective contact engineering techniques with proper SunsVoc characterization to evaluate the implied Voc and its effects on the cell's performance metrics along the SHJ contact management setup.