Progress of hydrogenation engineering in crystalline silicon solar cells: a review

Abstract

Crystalline silicon solar cells are always moving towards “high efficiency and low cost”, which requires continuously improving the quality of crystalline silicon materials. Nevertheless, crystalline silicon materials typically contain various kinds of impurities and defects, which act as carrier recombination centers. Therefore these impurities and defects must be well controlled during the solar cell fabrication processes to improve the cell efficiency. Hydrogenation of crystalline silicon is one important method to deactivate these impurities and defects, which is so-called “hydrogenation engineering” in this paper. Hydrogen is widely reported to be able to passivate diverse defects like crystallographic defects, metallic impurities, boron-oxygen related defects and etc, but the effectiveness of hydrogen passivation depends strongly on the processing conditions. Moreover, in this decade, advanced hydrogenation technique has been developed and widely applied in the photovoltaic industry to significantly improve the performance of silicon solar cells. As the research on hydrogenation study has made a significant progress, it is the right time to write a review paper on introducing the state-of-the-art hydrogenation study and its applications in photovoltaic industry. The paper first introduces the fundamental properties of hydrogen in crystalline silicon and then discusses the applications of hydrogen on deactivating/inducing typical defects (e.g. dislocations, grain boundaries, various metallic impurities, boron-oxygen related defects and LeTID) in p- and n-type crystalline silicon, respectively. At last, the benefits of hydrogenation engineering on the next-generation silicon solar cells (e.g. TOPCon and HJT solar cells) are discussed. Overall, it was found that hydrogen can deactivate most of typical defects (sometimes induce defect) in n- and p-type crystalline silicon, leading to a significant efficiency enhancement in PERC, TOPCon and HJT solar cells. In conclusion, the paper aims to assist young researchers to better understand hydrogenation research and shed light on the future development of hydrogenation study.

Dramatic Reduction of Silicon Surface Recombination by ALD TiOx Capping Layer from TiCl4 and H2O: The Role of Chlorine

“…In general, a combination of both is highly desirable for achieving outstanding passivation and, hence, high-efficiency Si solar cells. Currently, thin-film-passivated silicon surfaces are known to be able to achieve a high level of chemical passivation through hydrogenation, fluorination, or a combination of the two. In this study, we present novel findings that highlight the role of chlorination as an additional and previously less-known chemical passivation mechanism with broad applicability.…”

Passivating Silicon Tunnel Diode for Perovskite on Silicon Nip Tandem Solar Cells

“…Annealing the tunnel diode at 400 • C induces H diffusion (and/or exodiffusion) and depletes the H concentration in the nc-Si (n + ) layer, with still high H content at the tunnel diode oxide. Thus, we believe that the passivation recovery observed after such annealing could be explained by hydrogenation of the buried poly-Si/SiO x stack [23]. Annealing at 600 • C led to complete H effusion from the stacks, thus explaining why no passivation gain was observed for such a temperature.…”

A review of defect mitigation strategies for UMG-Si wafers

“…In recent years, significant progress has been made in developing a variety of defect mitigation strategies that target a wide range of defects and impurities. Detailed information on the progress of defect strategies can be found elsewhere (Wright et al, 2021;Liu et al, 2022;Song et al, 2022). This review will first examine a brief history and purification processes of UMG-Si.…”