Twisted bilayer blue phosphorene: A direct band gap semiconductor

• Bilayer stacked AA or AB blue phosphorene are indirect band gap semiconductor.
• Two rotated layers of blue phosphorene behave as a direct band gap semiconductor.
• The value of the band gap of two rotated layers of blue phosphorene changes with the angle.

We report that two rotated layers of blue phosphorene behave as a direct band gap semiconductor. The optical spectrum shows absorption peaks in the visible region of the spectrum and in addition the energy of these peaks can be tuned with the rotational angle. These findings makes twisted bilayer blue phosphorene a strong candidate as a solar cell or photodetection device. Our results are based on ab initio calculations of several rotated blue phosphorene layers.