Summary:
UCLA researchers in the Department of Chemistry & Biochemistry have developed a novel method for implementation of Van der Waals contact on commercial CdTe wafers for improved photovoltaic and solar panel production.
Background:
Cadmium Telluride (CdTe) is a common absorber used for thin-film optoelectronics and photovoltaics, including next-generation solar panels. CdTe accounts for over half of the thin-film photovoltaic market due to its rapid energy payback time. However, current CdTe solar cells are limited by their low open-circuit voltage (Voc), which directly constrains power conversion efficiency (PCE) and potential device performance. This is largely due to the intrinsic Fermi level pinning (FLP) effect caused by interfacial defects between CdTe and metal electrodes, leading to suboptimal contact. While Van der Waals (vdW) contacts have shown promise in overcoming the FLP effect, they are incompatible with the high surface roughness of commercial thin-film CdTe wafers. Attempts to polish the surface can damage the material, further reducing Voc and PCE. Additionally, conventional contacts are deeply integrated into existing manufacturing workflows, making the adoption of alternative methods difficult without scalable processes. Since incremental efficiency improvements lower cost per watt and increase commercial competitiveness, there is a need for a scalable method that enables vdW-contact formation on commercial thin-film CdTe wafers with high surface roughness.
Innovation:
To address these limitations, researchers at UCLA have developed a selenium-based buffer method that enables the formation of vdW contacts on CdTe wafers with high surface roughness. A selenium layer is utilized as a buffer to protect the substrate from metal-deposition induced damage and vaporization of the layer allows for bond-free semiconductor-metal vdW-contact. Using this approach, gold contacts applied to commercial CdTe wafers delivered meaningfully higher device performance than today’s standard designs, enabling greater power output without sacrificing the fast energy payback that makes CdTe solar technology economically attractive. Importantly, the selenium buffer layer methodology is simple, scalable, and compatible with current manufacturing infrastructure, showcasing its potential for widespread industrial adoption. Beyond photovoltaics, this approach is applicable to other delicate semiconductor applications that experience surface degradation from metallization, including III–V and II–VI compound semiconductors such as GaAs, InP, and HgCdTe. This invention demonstrates a scalable method for integrating vdW contacts onto rough, commercial semiconductor wafers, enabling damage-free metallization for high-performance CdTe solar cells and other surface-sensitive compound semiconductor devices using industry-compatible processes.
Potential Applications:
● Thin-film CdTe solar cells
● Next-generation photovoltaics
● IIIV & II-VI compound semiconductor devices
○ GaAs, InP, HgCdTe
● Optoelectronic devices (with fragile substrates)
○ Thin-film photodetectors, LEDs, sensors
● Rough surface semiconductor devices
Advantages:
● Reduced interfacial defect states
● Enhanced open-circuit voltage and power conversion efficiency
● Compatibility with commercial wafers
● Minimizes metallization process
● Scalable
○ Simple processing and integration with current manufacturing workflows
● Short energy payback time
● Broad applicability
○ Applicable to other delicate semiconductor systems
Development-To-Date: First successful demonstration of the invention completed.
Related Papers:
● Liu, Y., Guo, J., Zhu, E., Liao, L., Lee, S. J., Ding, M., Shakir, I., Gambin, V., Huang, Y., & Duan, X. (2018). Approaching the Schottky-Mott limit in van der Waals metal-semiconductor junctions. Nature, 557(7707), 696–700. https://doi.org/10.1038/s41586-018-0129-8
● Liu, Y., Huang, Y. & Duan, X. Van der Waals integration before and beyond two-dimensional materials. Nature 567, 323–333 (2019). https://doi.org/10.1038/s41586-019-1013-x
Reference:
UCLA Case No. 2025-173
Lead Inventors:
Yu Huang, Xiangfeng Duan