Improvement of Surface Passivation of Tunnel Oxide Passivated Contact Structure by Thermal Annealing in Mixture of Water Vapor and Nitrogen Environment

Abstract

The effects of post-crystallization annealing within various atmospheres on the surface passivation quality of tunnel oxide passivated contact (TOPCon) for crystalline silicon (c-Si) solar cells are studied. The results provide an innovative method for improving the surface passivation of the as-crystallized TOPCon structure by annealing at moderate temperatures ranging from 300 to 700 C within a mixture of water vapor and nitrogen atmosphere. The wet nitrogen improves the implied open-circuit voltages (iV oc ) from 700-710 to %730 mV on average and reduces the single-side reverse saturated recombination current density (J 0 ) to 3.8 fA cm À2 , which is much more effective than the so-called forming-gas annealing. In addition, the contact resistivity remains in low values of %5 mΩ cm 2 , ensuring its application in the high-efficiency c-Si solar cell. Secondary ion mass spectroscopy provides the evidence that the enhanced surface passivation by the water vapor annealing results from the hydrogen incorporation, which is logically believed to passivate the defects in the oxide and c-Si interface region. This study proposes a simple and cost-effective technique to improve the surface passivation of TOPCon structure, which is suitable for the high-efficiency c-Si solar-cell manufacture.

Hydrogenation Mechanisms of Poly‐Si/SiOx Passivating Contacts by Different Capping Layers

“…Hydrogenation treatments in c‐Si solar cell technology are often performed via forming gas annealing (FGA) of samples in a mixture of H 2 and inert gas, by annealing the samples without any capping layers in a mixture of water vapor and N 2 , or by depositing hydrogen‐rich capping layers such as AlO x :H or SiN x :H and annealing them in N 2 or FGA. Previously, we have noticed that in the case of low‐resistivity substrates (1 Ω cm), FGA of poly‐Si/SiO x passivating contacts resulted in little performance improvement, whereas others have reported a noticeable improvement .…”

Progress in p‐type Tunnel Oxide‐Passivated Contact Solar Cells with Screen‐Printed Contacts

“…[ 34 ] Alternatively, also, annealing of polysilicon layers in mixtures of water vapor and nitrogen has been reported to be effective in reducing overall carrier recombination. [ 35 ] The high iV oc level close to 700 mV reveals that the bulk lifetime for the p‐type wafer remains high despite the use of two thermal processes in the sequence, annealing of the polysilicon layer and POCl 3 diffusion. PL images did not show indication for ring structures; thus, the minority carrier lifetime in the bulk seems to not be strongly affected by oxygen precipitation.…”

Rapid‐Thermal‐Annealing‐Induced Passivation Degradation and Recovery of Polysilicon Passivated Contact with Czochralski and Cast Multicrystalline Silicon Substrates

“…Subsequently, the samples coated by the bifacial P-doped a-Si:H/SiO x layers were divided into three groups. Group1: the samples were annealed for crystallization in a conventional tube furnace at 820 C for 30 min followed by a slow cooling process and then hydrogenated with the moisture/nitrogen annealing at 450 C. [19] Afterward, the industrial belt-furnace firing procedure was simulated using an RTA process. Finally, the samples were subjected to the 820 C N 2 annealing, 450 C N 2 annealing, and 450 C moisture/nitrogen annealing, respectively.…”

“…Afterward, a single-sided SiN x capping layer was deposited at 450 C using PECVD. [12,17,19] Then, the samples were subjected to the RTA processes. Finally, the samples were also subjected to 820 C N 2 annealing, 450 C N 2 annealing, and 450 C moisture/nitrogen annealing, respectively.…”

“…[18] The poly-Si layer is normally formed by the high-temperature crystallization of nonhydrogenated amorphous silicon (a-Si) by LPCVD or sputtering, or a-Si:H by PECVD followed by a hydrogenation treatment to passivate the defects. [19,20] Moreover, an additional advantage of the industrial TOPCon SCs is the use of identical Al/Ag or Ag pastes as the PERC SCs in the metallization, which could simplify the manufacturing process. However, with the high-temperature rapid firing, equivalent to a process of rapid thermal annealing (RTA) to cure the metal pastes during the metallization, it is easy to cause a notable degradation in the passivation quality, [21,22] especially for the case with the PECVD-deposited poly-Si.…”