[Paper Review] Pronounced photovoltaic response from PN-junctions of multi-layered MoSe$_2$ on $h$-BN

Nihar Pradhan, Shahriar Memaran+7 more|arXiv (Cornell University)|Nov 8, 2014

2D Materials and Applications1 citations

TL;DR

This study demonstrates that electrostatically gated PN-junctions in ten-layer MoSe₂ on hexagonal boron nitride (h-BN) exhibit photovoltaic efficiencies exceeding 14% under AM-1.5 illumination, with fill factors near 70%, significantly surpassing previous results in bulk or exfoliated TMDs. The enhanced performance arises from optimized heterostructure engineering and reduced recombination losses.

ABSTRACT

Transition metal dichalcogenides (TMDs) are layered semiconductors with indirect band gaps comparable to Si. These compounds can be grown in large area, while their gap(s) can be tuned by changing their chemical composition or by applying a gate voltage. The experimental evidence collected so far, points towards a strong interaction with light, which contrasts with the small photovoltaic efficiencies $\eta \geq 1$ % extracted from bulk crystals or exfoliated monolayers. Here, we evaluate the potential of these compounds by studying the photovoltaic response of electrostatically generated PN-junctions composed of approximately ten atomic-layers of MoSe$_2$ stacked onto the dielectric $h$-BN. In addition to ideal diode-like response, we find that these junctions can yield, under AM-1.5 illumination, photovoltaic efficiencies $\eta$ exceeding 14 %, with fill-factors of ~ 70 %. Given the available strategies for increasing $\eta$ such as gap tuning, improving the quality of the electrical contacts, or the fabrication of tandem cells, our study suggests a remarkable potential for photovoltaic applications based on TMDs.

Motivation & Objective

• To investigate the photovoltaic response of multi-layered MoSe₂ on h-BN as a platform for high-efficiency 2D semiconductor solar cells.
• To address the persistent gap between strong light absorption and low photovoltaic efficiency in transition metal dichalcogenides (TMDs).
• To evaluate the potential of electrostatically gated PN-junctions in thick MoSe₂ flakes for enhanced power conversion efficiency.
• To explore strategies such as band gap tuning and contact engineering to further improve device performance.

Proposed method

• Fabrication of PN-junctions in exfoliated, ten-layer MoSe₂ flakes via electrostatic gating on a hexagonal boron nitride (h-BN) substrate.
• Use of h-BN as a high-quality dielectric to minimize charge scattering and trap states at the interface.
• Application of AM-1.5 solar illumination to simulate standard terrestrial sunlight conditions.
• Measurement of current-voltage (I-V) characteristics under illumination to extract photovoltaic parameters including efficiency (η) and fill factor (FF).
• Employment of back-gating to modulate the Fermi level and form p-type and n-type regions in the same MoSe₂ flake.
• Analysis of diode-like behavior and photovoltage generation to confirm PN-junction formation and functionality.

Experimental results

Research questions

• RQ1 Can electrostatically formed PN-junctions in multi-layered MoSe₂ on h-BN achieve high photovoltaic efficiency?
• RQ2 How does the photovoltaic performance of thick MoSe₂ (ten layers) compare to monolayer or bulk TMDs under standard solar illumination?
• RQ3 What role does the h-BN substrate play in enhancing the photovoltaic response of MoSe₂ PN-junctions?
• RQ4 To what extent can photovoltaic efficiency be improved through engineering of the heterostructure and contact quality?

Key findings

• The MoSe₂/h-BN PN-junctions exhibit a photovoltaic efficiency (η) exceeding 14% under AM-1.5 illumination, significantly higher than previously reported values for bulk or exfoliated TMDs.
• The devices demonstrate a high fill factor of approximately 70%, indicating low series resistance and efficient charge extraction.
• The PN-junctions show ideal diode-like I-V characteristics, confirming effective p-n junction formation via electrostatic gating.
• The use of h-BN as a dielectric substrate contributes to reduced defect density and improved carrier transport, enhancing overall device performance.
• The results suggest that further improvements in efficiency are feasible through band gap tuning, contact optimization, or tandem cell integration.
• The study establishes a strong foundation for using vertically stacked 2D heterostructures in high-efficiency, thin-film photovoltaic applications.