Nanoscale SiO_x Tunnel Oxide Deposition Techniques and Their Influence on Cell Parameters of TOPCon Solar Cells

The main goal of solar cell technology is to attain high efficiency, long durability, mass-production, cost-effectiveness, and made with eco-friendly materials. Among the various crystalline silicon solar cell technologies, Tunneling Oxide Passivated Contact (TOPCon) solar cell has its unique style in terms of the structure and carrier transport manner, which predominately decreases the metal contact recombination and gives 1-D carrier transport. A very high efficiency of 26% for TOPCon solar cells has been achieved with the industrial screen print technology and obtained high cell parameter values of V_oc and fill factor as 732.3 mV and 84.3% respectively. The tunnel oxide thickness (maintaining < 2 nm) in the TOPCon has its prior impact on the efficiency and electrical parameters of the cell. To obtain the preferable thickness of the tunnel oxide layer various deposition techniques have been reported in the literature. SiO_x is the most widely used tunnel oxide material for TOPCon solar cells to date. In this review, different deposition methods that were used for the SiO_x tunnel oxide layer such as chemical oxidation, ozone oxidation, thermal oxidation, and plasma-enhanced chemical vapor deposition (PECVD) are elaborated. Moreover, the effect of the deposition conditions on the cell parameters in different techniques are also discussed briefly. Furthermore, the development of TOPCon solar cells and the latest reports that were used different tunnel oxide materials in finding an alternative to SiO_x tunnel oxide is discussed.