Comparing the Gettering Effect of Heavily Doped Polysilicon Films and Its Implications for Tunnel Oxide‐Passivated Contact Solar Cells

Abstract

In addition to excellent surface passivation and carrier selectivity, the structure based on the heavily doped polysilicon layer on an ultrathin silicon oxide interlayer also demonstrates strong impurity gettering effects. Herein, the gettering strength of a range of phosphorus‐ or boron‐doped polysilicon films from different fabrication techniques is assessed and compared. Iron, one of the most common metallic impurities in silicon, is used as a tracer impurity to quantify the gettering strength (segregation coefficient). A comparison of the experimental results to the literature, combined with measurements of the electrically active and inactive dopant concentrations, enables us to suggest the main gettering mechanisms in different polysilicon films. The differences in the segregation coefficients of the phosphorus‐doped polysilicon films for iron are within one order of magnitude, in spite of their different combinations of gettering mechanisms. On the other hand, boron‐doped polysilicon films show a large variation in their gettering effects, although the predominant gettering mechanisms are all attributed to electrically inactive boron, according to the current understanding of the gettering mechanisms from the literature. Finally, the impact of different polysilicon gettering effects on the efficiency of tunnel oxide‐passivated contact (TOPCon) cells is simulated and discussed.

A review of defect mitigation strategies for UMG-Si wafers

“…In the case of TOPCon structure, TR was incorporated as a pre-treatment step to mitigate the bulk degradation during subsequent high temperature processes, such as boron diffusion and TOPCon layers formation. Further, gettering effect provided by phosphorus doped polysilicon layers helped to mitigate the impact of metal impurities (Yang et al, 2023), Hayes et al (2019). The combined effect of TR and gettering effects and better passivation by TOPCon layers helped to achieve a similar V oc of 679 mV and 683 mV for solar cells based on UMG-Cz-Si and EG-Cz-Si, respectively.…”

“…Frontiers in Photonics frontiersin.org layers (both polarities) are known to provide strong gettering effects (Yang et al, 2023;Hayes et al, 2019).…”

Dual-purpose tunnel oxide passivated contact on silicon photoelectrodes with high photovoltages for tandem photoelectrochemical devices enabling unassisted water splitting

“…The TOPCon is applied on both sides of n-Si substrate to maximize the passivation effect, and the thickness of the SiO 2 layer is kept to be lower than 2 nm to allow a high probability of tunneling. In addition, when subjected to a high temperature, intrinsic impurities 44 in n-Si wafer (and even extrinsic impurities 43 introduced during device preparation) can diffuse across the SiO 2 and be collected by polycrystalline Si. This gettering of impurities helps further purify the n-Si wafer and increases the lifetime of charge carriers.…”

“…41 In the case of MIS, because of the presence of an insulating layer in the structure which can serve as a diffusion barrier, it exhibits higher thermal stability than other congurations. [41][42][43][44] However, little attention has been paid to achieving both high photovoltage and thermal stability.…”