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Theory of bulk photovoltaic effect in Anderson insulator

Significance Localization and its effect on electronic transport is a key for understanding the properties of disordered systems. In this work, we theoretically study the bulk photovoltaic effect in Anderson insulators, which occurs when a weak dissipation exists. Despite the localization of all wavefunctions, the photocurrent is nearly independent of the impurity strength when it is smaller than the bandwidth. This current vanishes in the absence of dissipation, while it reaches a value comparable to that of the clean limit with a dissipation expected at room temperature, assuming electron–phonon interaction causes the dissipation. These results are consistent with a recent experiment in SbSI. The results open a direction for designing efficient optical devices with a suppressed carrier backflow. The localization of wavefunction by disorder makes a conductive material an insulator with vanishing conductivity at zero temperature. A similar outcome is expected for the photocurrent in semiconductor p-n junctions because the photoexcited carriers cannot drift through the device. In contrast, we here show numerically that the bulk photovoltaic effect—the photovoltaic effect in noncentrosymmetric bulk materials—occurs in a noncentrosymmetric, disordered, one-dimensional insulator where all eigenstates are localized. We find this photocurrent remains, even when the energy scale of random potential is larger than the bandwidth. On the other hand, the photocurrent decays exponentially when the excitation is local, i.e., when only a part of the device is illuminated. The photocurrent also vanishes if the relaxation occurs only by contact with the electrodes. Our result implies that the ratio of the photovoltaic current and the direct current by the variable-range hopping increases with decreasing temperature. These results suggest a route to design high-efficiency solar cells and photodetectors.