Performance Investigation of Alkali Metal Fluorides as Alternate Electron Selective Contacts for TOPCon Solar Cells

The recombinations at metallized contacts are the final hurdles before reaching the Shockley Queisser limit in silicon solar cells. The domination of market by silicon cells calls for developing techniques and methodologies to overcome these bottlenecks and induce additional life to silicon based designs. A myriad of contact schemes targeting this limitation have evolved in the last decade. The fundamental of these contacts is based on carrier selectivity, passivation and resistivity they provide to the two types of carriers. One of the emerging contact design is the TOPCon (Tunnel Oxide Passivating contact) configuration which uses polysilicon layers separated by thin oxide to induce selective extraction of carriers. However the use of polysilicon layers leads to higher parasitic absorption thus restricting their use at the front contact of the solar cell. Keeping this in mind, we herein have investigated the performance of an emerging class of materials called Alkali Metal Fluorides (AMF) as alternate front side electron selective contacts for TOPCon solar cells. For this study, Lithium Fluoride (LiFx) has been chosen due to its wide bandgap and low work function which make it a potential electron selective candidate. The electrostatics and transport of the carriers in the proposed design is studied and numerical simulations are performed to understand the effect of parameter variations on the figures of merit. It is deduced that the cell using LiFx as the front electron selective layer shows improved performance parameters in comparison to double sided TOPCon design, making AMF interesting contenders for high efficiency photovoltaics.