Ishizuka Hiroaki, Nagaosa Naoto
Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139;
Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan.
Proc Natl Acad Sci U S A. 2021 Mar 9;118(10). doi: 10.1073/pnas.2023642118.
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.
无序导致的波函数局域化会使导电材料在零温度下成为电导率消失的绝缘体。对于半导体 p-n 结中的光电流，预计会有类似的结果，因为光激发载流子无法在器件中漂移。相比之下，我们在此通过数值计算表明，体光伏效应（非中心对称体材料中的光伏效应）发生在所有本征态都局域化的非中心对称、无序的一维绝缘体中。我们发现，即使随机势的能量尺度大于带宽，这种光电流仍然存在。另一方面，当激发是局域的，即仅器件的一部分被光照时，光电流呈指数衰减。如果弛豫仅通过与电极接触发生，光电流也会消失。我们的结果表明，光伏电流与变程跳跃产生的直流电流之比会随着温度降低而增加。这些结果为设计高效太阳能电池和光电探测器提供了一条途径。
