  Photogalvanic effect (PGE) occurring in noncentrosymmetric materials enables
the generation of the open-circuit voltage that is much larger than the
bandgap, making it rather attractive in solar cells. However, the magnitude of
the PGE photocurrent is usually small, which severely hampers its practical
application. Here we propose a mechanism to largely enhance the PGE
photocurrent by mechanical strain based on the quantum transport simulations
for the two-dimensional nickel-phosphorene-nickel photodetector. Broadband PGE
photocurrent governed by the Cs noncentrosymmetry is generated at zero bias
under the illumination of linearly polarized light. The photocurrent depends
linearly on the device asymmetry, while nonlinearly on the optical absorption.
By applying the appropriate mechanical tension stress on the phosphorene, the
photocurrent can be substantially enhanced by up to 3 orders of magnitude,
which is primarily ascribed to the largely increased device asymmetry. The
change in the optical absorption in some cases can also play a critical role in
tuning the photocurrent due to the nonlinear dependence. Moreover, the
photocurrent can even be further enhanced by the mechanical bending, mainly
owing to the considerably enhanced device asymmetry. Our results reveal the
dependence of the PGE photocurrent on the device asymmetry and absorption in
transport process through a device, and also explore the potentials of the PGE
in the self-powered low-dimensional flexible optoelectronics.
