Key materials and device structures of crystalline silicon heterojunction solar cells.

As photovoltaics (PVs) made out of crystalline silicon (c-Si) have become more commonplace, the past decade has witnessed leaps and bounds in performance advances, the majority of which have been focused on lowering the losses associated with the directly metallized and/or heavily doped regions seen in typical devices. There are a number of recent developments that have the potential to greatly enhance the efficiencies of commercially available thin-film c-Si solar cells, including passivating contact featuring stacks of polysilicon (poly-Si)/SiO_x, commonly abbreviated as TOPCon (tunnel oxide passivated contacts), which has led to efficiencies of over 26% and 24% being achieved by lab-based and industrial cells, respectively. This paper provides an outline of the evolution of this structure, which dates back to the 1980s, and a description of the present status of this technique in the lab and in industry. While the future of poly-Si junctions seems to be bright, as predicted by the International Technology Roadmap for Photovoltaics, various difficulties remain unresolved, such as the preparation of poly-Si and metallization issues. Additionally, this review discusses the remaining hurdles and the potential for poly-Si junctions to revolutionize the PV industry.

Due to stable and high power conversion efficiency (PCE), it is expected that silicon heterojunction (SHJ) solar cells will dominate the photovoltaic market. So far, the highest PCE of the SHJ‐interdigitated back contact (IBC) solar cells has reached 26.7%, approximately approaching the theoretical Shockley–Queisser (SQ) limitation of 29.4%. To break through this limit, multijunction devices consisting of two or three stacked subcells have been developed, which can fully utilize the sunlight by absorbing different parts of the solar spectrum. This article provides a comprehensive overview of current research on SHJ‐based tandem solar cells (SHJ‐TSCs), including perovskite/SHJ TSCs and III–V/SHJ TSCs. Firstly, we give a brief introduction to the structures of SHJ‐TSCs, followed by a discussion of fabrication processes. Afterwards, we focus on various materials and processes that have been explored to optimize the electrical and optical performance. Finally, we highlight the opportunities and challenges of SHJ‐TSCs, as well as personal perspectives on the future development directions in this field.

In this review, the morphology, composition and microstructure of buried interface are discussed, and the effective passivation strategies and corresponding mechanisms are summarized systematically.