High open-circuit voltage in transition metal dichalcogenide solar cells

TL;DR

This paper reports a record-high open-circuit voltage of 1.02 V in a 120 nm MoS2 homojunction solar cell, highlighting the potential of layered TMDCs for ultra-thin, high-efficiency photovoltaics.

Contribution

It demonstrates a high open-circuit voltage in doped MoS2 homojunctions, surpassing typical values, and explains the role of band alignment and doping in achieving this performance.

Findings

Achieved 1.02 V open-circuit voltage in MoS2 homojunctions.

Doped MoS2 exhibits electroluminescence despite indirect bandgap.

Illumination of contacts reduces open-circuit voltage, indicating photoactivity.

Abstract

The conversion efficiency of ultra-thin solar cells based on layered materials has been limited by their open-circuit voltage, which is typically pinned to a value under 0.6 V. Here we report an open-circuit voltage of 1.02 V in a 120 nm-thick vertically stacked homojunction fabricated with substitutionally doped MoS2. This high open-circuit voltage is consistent with the band alignment in the MoS2 homojunction, which is more favourable than in widely-used TMDC heterostructures. It is also attributed to the high performance of the substitutionally doped MoS2, in particular the p-type material doped with Nb, which is demonstrated by the observation of electroluminescence from tunnelling graphene/BN/MoS2 structures in spite of the indirect nature of bulk MoS2. We find that illuminating the TMDC/metal contacts decreases the measured open-circuit voltage in MoS2 van der Waals homojunctions because they are photoactive, which points to the need of developing low-resistance, ohmic contacts to doped MoS2 in order to achieve high efficiency in practical devices. The high open-circuit voltage demonstrated here confirms the potential of layered transition-metal dichalcogenides for the development of highly efficient, ultra-thin solar cells.