A recent study in Light | Science & Applications explores how edge semimetal contacts can enhance the bulk photovoltaic effect (BPVE) in transition metal dichalcogenides (TMDs), addressing the limitations of conventional solar cells and advancing photovoltaic efficiency.
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Advancements in Photovoltaic Technology
The BPVE is a phenomenon where electric current is generated under illumination in non-centrosymmetric materials, independent of an internal electric field. This effect is not constrained by the Shockley-Queisser efficiency limit (approximately 33 %) that applies to traditional solar cells. Historically, BPVE research focused on ferroelectric oxides, but advancements in two-dimensional (2D) materials, particularly TMDs, have expanded its potential.
TMDs like molybdenum disulfide (MoS2) and tungsten disulfide (WS2) possess unique electronic and optical properties that make them important for photovoltaic applications. Their layered structures enable efficient charge carrier transport, and their polarization enhances the BPVE. However, challenges like non-Ohmic contacts and low photocurrent generation limit their practical implementation.
This study addresses these limitations by exploring the use of edge semimetal contacts, specifically with bismuth (Bi) and gold (Au), to enhance BPVE performance in 3R-MoS2.
About the Research
The study investigated the impact of electrode configurations on BPVE in 3R-MoS2 by fabricating two device types: top contact (TC) and edge contact (EC).
Exfoliated 3R-MoS2 flakes were transferred onto a silicon dioxide substrate. Long flakes with uniform thickness and widths were used to ensure consistency. The alignment of the armchair direction of the flakes with the device channel was verified using second harmonic generation (SHG). Electron beam lithography was used to pattern electrodes, and high-resolution transmission electron microscopy (HRTEM) analyzed the device structures.
Photovoltaic performance was evaluated using current-voltage (I-V) measurements under dark and illuminated conditions, with a linearly polarized laser as the illumination source to assess photocurrent responses relative to laser polarization.
Key Findings and Insights
The study demonstrated significant enhancement in the BPVE for the EC configuration compared to the TC configuration. Under laser illumination, the EC device achieved a short-circuit photocurrent (Isc) of 1.26 µA and an open-circuit photovoltage (Voc) of 39.44 mV. In comparison, the TC device exhibited an Isc of 48.11 nA and a Voc of 1.65 mV. These outcomes highlight the superior performance of the EC configuration.
Additionally, the researchers analyzed the relationship between the thickness of 3R-MoS₂ and the BPVE. They observed a linear increase in photocurrent for the EC device with increasing material thickness, reaching a maximum of 6.36 µA at 40 nm.
This behavior corresponded with the material's absorption characteristics, indicating that the EC configuration facilitates more effective carrier collection and transport. Furthermore, the low contact resistance between Bi and 3R-MoS₂ enhanced charge transfer efficiency.
The authors also explored the interaction between BPVE and conventional photovoltaic effects (PVE) by designing a 3R-MoS2 or WSe2 heterojunction. BPVE was shown to significantly contribute to overall photocurrent, highlighting its potential for integration into hybrid photovoltaic designs.
Applications of Enhanced BPVE
The advancements in BPVE demonstrated in this study provide a foundation for next-generation photovoltaic devices. The use of edge semimetal contacts enables the development of high-efficiency solar cells capable of surpassing traditional efficiency limits. TMDs, particularly with optimized electrode configurations, have broad potential applications in optoelectronic devices such as photodetectors and energy harvesting systems.
Future Directions
This research highlights the potential of enhancing BPVE in TMDs through edge semimetal contacts, with significant improvements in photocurrent and photovoltage performance. Future efforts should focus on refining electrode materials and configurations to further optimize BPVE. Additionally, exploring other 2D materials and heterostructures could uncover new mechanisms to improve photovoltaic efficiency and drive advancements in sustainable energy technologies.
Journal Reference
Qiao, S., et al. (2025). Boosting bulk photovoltaic effect in transition metal dichalcogenide by edge semimetal contact. Light Sci Appl. DOI: 10.1038/s41377-024-01691-z, https://www.nature.com/articles/s41377-024-01691-z
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