A recent study published in the journal Light | Science & Applications explores how edge semi-metallic contacts can enhance the bulk photovoltaic effect (BPVE) in transition metal dichalcogenides (TMDs), addressing limitations in conventional solar cells and improving their photovoltaic performance.
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Advances in solar power generation technology
BPVE is a phenomenon in which current is generated by irradiation in non-centrosymmetric materials, independent of the internal electric field. This effect is not limited by the Shockley-Queisser efficiency limit (~33%) that applies to conventional solar cells. Traditionally, BPVE research has focused on ferroelectric oxides, but advances in two-dimensional (2D) materials, especially TMDs, have expanded its possibilities.
TMDs such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2 ) are important for photovoltaic applications due to their unique electronic and optical properties. Their layered structure allows efficient charge carrier transport and their polarizability increases the BPVE. However, challenges such as non-ohmic contacts and low photocurrent generation limit their practical implementation.
In this work , we address these limitations by exploring the use of edge semimetallic contacts, specifically using bismuth (Bi) and gold (Au), to improve the BPVE performance of 3R -MoS2 .
About the Research
In this study, two types of devices, top contact (TC) and edge contact (EC), were fabricated to investigate the effect of electrode configuration on the BPVE of 3R-MoS2.
Exfoliated 3R-MoS2 flakes were transferred onto silicon dioxide substrates. Long pieces of uniform thickness and width are used for consistency. The armchair orientation of the fragments and the alignment of the device channels were verified using second harmonic generation (SHG). Electron beam lithography was used to pattern the electrodes, and high-resolution transmission electron microscopy (HRTEM) was used to analyze the device structure.
The photovoltaic performance was evaluated using current-voltage (IV) measurements in dark and light conditions, and a linearly polarized laser was used as the illumination source to evaluate the photocurrent response and laser polarization.
Key findings and observations
This study demonstrates a significant improvement in the BPVE of 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 Isc of the TC device is 48.11 nA and Voc is 1.65 mV. These results highlight the superior performance of the EC configuration.
Furthermore, the researchers analyzed the relationship between the thickness of 3R-MoS₂ and BPVE. They observed that the photocurrent of the EC device increased linearly as the material thickness increased, reaching a maximum of 6.36 µA at 40 nm.
This behavior corresponds to the absorption characteristics of the material, suggesting that the EC configuration allows for more efficient carrier collection and transport. Furthermore, the low contact resistance between Bi and 3R-MoS₂ improves the charge transfer efficiency.
The authors also investigated the interplay between BPVE and the conventional photovoltaic effect (PVE) by engineering 3R-MoS2 or WSe2 heterojunctions. BPVE was shown to contribute significantly to the overall photocurrent, highlighting its potential integration into hybrid photovoltaic designs.
Advanced BPVE Applications
The advances in BPVE demonstrated in this work provide the foundation for next-generation photovoltaic devices. The use of edge semi-metallic contacts will enable the development of high-performance solar cells that exceed traditional performance limits. TMDs have many potential applications in optoelectronic devices such as photodetectors and energy harvesting systems, especially if the electrode configuration is optimized.
Future Directions
This work highlights the potential to enhance the BPVE of TMDs via edge semi-metallic contacts to significantly improve their electro-optical and photovoltaic performance. Future efforts should focus on refining the electrode materials and configurations to further optimize the BPVE. Furthermore, exploration of other 2D materials and heterostructures may reveal new mechanisms to improve photovoltaic performance and facilitate advances in sustainable energy technologies.
Reference magazines
Qiao, S., et al . (2025). Enhancement of bulk photovoltaic effect in transition metal dichalcogenides by edge semimetal contacts. Photonics Applications DOI: 10.1038/s41377-024-01691-z, https://www.nature.com/articles/s41377-024-01691-z
