Symmetry-breaking-enhanced power conversion efficiency of 2D van der Waals heterostructures

Symmetry-breaking plays a crucial role in determining the property and functionality of materials. Here, we demonstrate that symmetry-breaking can dramatically enhance the power conversion efficiency (PCE) of a two-dimensional (2D) van der Waals (vdW) heterostructure solar cell by taking a γ-phosphorus-carbide (PC)-based vdW heterostructure as a model. Thanks to its four-atom-layer structure of γ-PC, both alternately arranging P and C atoms to form a Janus structure and sliding C atom layer to change space group are two effective methods to break the symmetry. We find that in comparison with a symmetric configuration, the PCE of γ-PC/MoS2N4 with symmetry-breaking could be increased by 257.2% and 270% via forming a Janus structure and the change in space group, respectively. Particularly, the PCE of symmetry-broken γ-PC/MoSi2N4 can be further increased to 21.35% under an appropriate tensile strain, which could be attributed to small conduction band offset between constituent monolayers and suitable donor bandgap. Our study showcases that tuning the symmetry of multi-atom-layer 2D materials is an effective strategy to realize enhancement of the performance for 2D materials-based optoelectronic devices.