Screening two-dimensional pyroelectric materials based on pentagonal chains with large shift current

The bulk photovoltaic effect (BPVE) of two-dimensional (2D) polar crystals has received considerable attention in recent years due to its potential applications in high-efficiency energy harvesting. Here, we propose a class of pentagonal chain-based 2D pyroelectric $\mathrm{Cu}X{X}^{\ensuremath{'}}Y$ $(X, {X}^{\ensuremath{'}}=\mathrm{S},\mathrm{Se},\mathrm{Te};Y=\mathrm{Cl},\mathrm{Br},\mathrm{I})$ monolayers with in-plane polarization via a high-throughput screening method. By using first-principles calculations, we show that compared to the 2D nonpolar $\mathrm{Cu}{X}_{2}Y$ compounds, the alignment between the averaged transition intensity and shift vector of the polar $\mathrm{Cu}X{X}^{\ensuremath{'}}Y$ materials gives rise to the enhanced shift current responses reaching up to $500\phantom{\rule{0.16em}{0ex}}\textmu{}\mathrm{A}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{--2}$ in the visible range, and the magnitude of the shift current is positively related to the polarity of the $X\ensuremath{-}{X}^{\ensuremath{'}}$ bond. More importantly, we find that all the studied materials have their exfoliation energies comparable to those of existing 2D materials, implying the feasibility for preparing $\mathrm{Cu}X{X}^{\ensuremath{'}}Y$ monolayers by mechanical exfoliation. Our study demonstrates the potential of utilizing pentagonal chains in the design of polar materials with strong BPVE responses.