Boosting bulk photovoltaic effect in transition metal dichalcogenide by edge semimetal contact

Oxide materials with a non-centrosymmetric structure exhibit bulk photovoltaic effect (BPVE) but with a low cell efficiency. Over the past few years, relatively larger BPVE coefficients have been reported for two-dimensional (2D) layers and stacks with asymmety-induced spontaneous polarization. Despite these achievements, the full potential of TMDs in the BPVE has not yet been realized, and several fundamental issues remained to be resolved. One is the typical non-Ohmic contacts between metals and TMDs due to the strong pinning effect of the Fermi levels. The 2^nd is that previous devices have typically adopted top contact (TC) electrodes, which may not fully utilize the polarization within TMDs. The 3^rd is that the typical way to break the in-plane symmetry for inducing BPVE in these 2D materials is through non-scalable method to add external strain. Here, we report a crucial breakthrough in boosting the BPVE in 3R-MoS₂ by adopting edge contact (EC) geometry using bismuth semimetal electrode. In clear contrast to the typically used top contact (TC) geometry, the EC metal which strongly adheres to the edges and the subtrates can induce a pronounced tensile strain to the 3R-MoS₂, and the lateral contact geometry allows to completely access to in-plane polarization from underneath layers reachable by light, leading to >100 times of BPVE enhancement in photocurrent. We further design a 3R-MoS₂/WSe₂ heterojunction to demonstrate constructive coupling of BPVE with the conventional photovoltaic effect, indicating their potential in photodetectors and photovoltaic devices.