Crucial Contribution of Polarity for the Bulk Photovoltaic Effect in a Series of Noncentrosymmetric Two-Dimensional Organic-Inorganic Hybrid Perovskites

The bulk photovoltaic effect (BPVE) is a promising optoelectronic phenomenon that produces a steady-state photocurrent in homogeneous bulk materials without the application of an electric field. In principle, the BPVE is allowed to be observed in noncentrosymmetric systems. However, guidelines on the effectiveness of crystal symmetry for the BPVE, such as chirality and polarity, remain unknown because of the lack of systematically controllable materials. For this reason, three types of noncentrosymmetric two-dimensional organic-inorganic hybrid perovskites (2D-OIHPs) of lead iodides with the formula A2PbI4 and chiral ammonium cations (A+) were used in the experiments. These were classified as (i) achiral-polar systems, (ii) chiral-nonpolar systems, and (iii) chiral-polar systems. All systems showed a strong current enhancement under light irradiation and an electric field. However, only (i) and (iii) systems showed the BPVE. Furthermore, direction reversal of the detected zero-bias photocurrent (I0) was observed when the direction of the electric polarization was changed. The absence of the detected BPVE in the (ii) system can be attributed to the zero net electric polarization (P) of the crystal structure, whereas (i) and (iii) systems possess nonzero P. Based on these observations, the features of the BPVE in 2D-OIHP lead iodides demonstrated in this work could be interpreted using the shift current mechanism.