On March 14, a joint research team from DAS Solar, Hebei University led by Professor Jianhui Chen, and Germany's Forschungszentrum Jülich published a major study in Nature Communications titled "Passivating pinholes for large-area and high-efficiency TOPCon solar cells".
Following years of focused research, the team reports the first identification of a previously unrecognized physical phenomenon at the TOPCon interface, termed passivating pinholes. These structures enable efficient carrier transport while maintaining strong surface passivation. The discovery resolves a longstanding question in TOPCon interface physics and provides both a theoretical foundation and a practical pathway for further efficiency gains, marking a significant advance in high-efficiency silicon photovoltaics.
The work brings new clarity to one of the most critical aspects of TOPCon device design. As tunnel oxide passivated contact (TOPCon) technology has become the dominant high-efficiency architecture—accounting for the majority of global crystalline silicon production by 2025—its performance has been closely tied to the properties of the ultrathin SiOₓ layer and the heavily doped polysilicon (Poly-Si) contact stack. For years, microscopic pinholes in the SiOₓ layer were widely regarded as detrimental defects, believed to compromise passivation quality, reduce open-circuit voltage, and ultimately limit efficiency. Because such pinholes were also considered unavoidable, they were seen as an intrinsic constraint on further TOPCon improvements.
This study challenges that assumption. Leveraging complementary strengths in industrial-scale cell development, advanced materials characterization, and simulation, the joint team demonstrates that not all pinholes are equal. Instead, their impact depends on their atomic configuration and chemical environment.
Using aberration-corrected transmission electron microscopy (AC-TEM), the researchers conducted atomic-level imaging of the SiOₓ/Poly-Si interface and identified two distinct types of pinholes. The first, referred to as recombination pinholes, are characterized by oxygen depletion and direct contact between polysilicon and crystalline silicon, resulting in a high density of dangling bonds and increased carrier recombination.
The second type—passivating pinholes—was observed and defined for the first time in this study. Although these regions involve localized thinning or disruption of the oxide layer, they retain sufficient oxygen to effectively passivate dangling bonds while simultaneously allowing carriers to tunnel through efficiently. This dual functionality overturns the conventional view that pinholes are inherently harmful. Instead, the findings show that properly passivated pinholes can improve interface properties, suppress recombination, and enhance both open-circuit voltage and overall cell efficiency.
By establishing that the key factor is not the presence of pinholes per se, but whether they are passivated, the study provides a new framework for interface engineering in TOPCon cells. This insight offers clear guidance for process optimization and opens a viable route toward further performance improvements in large-area devices.
The research was supported in part by a provincial-level R&D program focused on key TOPCon technologies for mass production, aimed at bridging the gap between fundamental research and industrial deployment. In early 2024, DAS Solar and Hebei University also established a joint photovoltaic research center to address critical challenges in device physics and manufacturing, creating a collaborative model that integrates academic research with industrial application and accelerates technology transfer.
Dr. Dengyuan Song, CTO of DAS Solar and corresponding author of the paper, commented that the breakthrough highlights the value of close collaboration between industry and academia. He noted that the company continues to advance a multi-path technology strategy anchored in TOPCon, alongside back-contact architectures and tandem technologies. To date, TOPCon mass-production cell efficiency has exceeded 27%, while its DBC technology has reached cell efficiencies above 27.77% and module efficiencies beyond 24.8%.
Publication in Nature Communications underscores the growing maturity of research into TOPCon interface physics and its relevance to industrial performance. Looking ahead, DAS Solar plans to continue investing in core photovoltaic technologies while expanding applications across diverse environments, supporting the broader transition toward higher-efficiency, lower-cost, and more sustainable solar energy systems worldwide.