Strain-Engineered Quasiparticle Band Structure and Electron–Hole Excitation in Hittorf’s Phosphorene for Efficient Photon-to-Electricity Conversion

Exciton-driven strong light–matter interactions in two-dimensional materials have displayed their advantages in applications in optoelectronics and photonics. However, the large exciton binding energy prohibits the efficient separation of photoexcited electron–hole pairs and is unfavorable for the application of photoelectrics and photovoltaics. Here, based on density-functional theory with the many-body perturbation method, we study the evolution of quasiparticle band structure, exciton, and optical properties with biaxial strain in 2D Hittorf's phosphorene. The pristine and +1% strained Hittorf's phosphorene are direct-band-gap semiconductors with the valence band maximal and the conduction band minimal located at the X point. When strain is approaching +2%, the conduction band minimal changes from the X point to the Γ point, resulting in a transition to the indirect band gap. This kind of indirect band gap persists to +5%. For the optical gap, we observe a modulation threshold of 0.33 eV over a +5% strain range. It is revealed that a p–n junction with efficient electron–hole excitation and separation is naturally formed in inhomogeneously strained 2D membrane. The transition from direct-band-gap to indirect-band-gap semiconductor, the strongly enhanced exciton lifetime, and the spatial separation of photoexcited electron–hole pairs under a moderate electric field will further inhibit the recombination. Together with the efficient visible light absorption which guarantees the absorption of solar spectra, these findings provide an effective avenue toward solar energy harvesting.