Abstract
MoS2 is a layered two-dimensional semiconductor with a direct band gap of 1.8 eV. The MoS2/bulk semiconductor system offers a new platform for solar cell device design. Different from the conventional bulk p-n junctions, in the MoS2/bulk semiconductor heterostructure, static charge transfer shifts the Fermi level of MoS2 toward that of bulk semiconductor, lowering the barrier height of the formed junction. Herein, we introduce hexagonal boron nitride (h-BN) into MoS2/GaAs heterostructure to suppress the static charge transfer, and the obtained MoS2/h-BN/GaAs solar cell exhibits an improved power conversion efficiency of 5.42%. More importantly, the sandwiched h-BN makes the Fermi level tuning of MoS2 more effective. By employing chemical doping and electrical gating into the solar cell device, PCE of 9.03% is achieved, which is the highest among all the reported monolayer transition metal dichalcogenide based solar cells.
Highlights
Tunable Fermi level is one of the unique physical properties of 2D materials, which can be finely tuned by chemical doping or electrical gating[27,28,29,30]
Different from the traditional p-n junctions and metal/semiconductor Schottky junctions, the charge transfer between MoS2 and the GaAs substrate can greatly influence the position of Fermi level in the 2D material, which leads to a much lower barrier height than the ideal value originated from the Fermi level difference
The barrier height is a key factor for the electrical properties of electronic and optoelectronic devices
Summary
Tunable Fermi level is one of the unique physical properties of 2D materials, which can be finely tuned by chemical doping or electrical gating[27,28,29,30]. Different from the conventional bulk p-n junctions, there is static charge transfer between 2D materials and bulk semiconductor, which could severely lower the Fermi level difference between bulk semiconductor and 2D material[31], and lead to a decreased junction barrier height. The photovoltaic performance of the heterojunction is greatly influenced by the junction barrier height, which means suppressing the static charge transfer between 2D materials and semiconductor substrate are highly desirable. The inserted h-BN layer makes the tuning of Fermi level of MoS2 more effective, which greatly improves the performance of solar cells. Based on the interface band structure designing and Fermi level tuning of MoS2, 9.03% of PCE has been achieved
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