Enhancing the Photovoltaic Performance of Directional-Growing Two-Dimensional Perovskites by Out-of-Plane Polarization

Two-dimensional (2D) perovskites have great application potential in the photovoltaic field, but the carriers can only be transmitted in-plane due to the limitation of the quantum well structure. It is usually necessary to induce a vertical orientation in photovoltaic devices to overcome this limitation. Here we find that the carrier limitation of 2D perovskites can be overcome by out-of-plane polarization. 4-(Aminomethyl)piperidiniumPbI₄ (4-AMPI) is a low-band-gap 2D perovskite ferroelectric with out-of-plane polarization. In this work, 4-AMPI was annealed at different temperatures to fabricate photovoltaic devices growing along different crystal planes. Under the irradiation of AM 1.5G, the parallel-grown 4-AMPI films exhibit a photocurrent density comparable to that of vertically grown films, indicating that out-of-plane polarization can help carriers overcome quantum well constraints. Compared with the nonferroelectric 3-(aminomethyl)piperidiniumPbI₄ (3-AMPI), the photocurrent density of 4-AMPI with out-of-plane polarization is significantly higher, which is attributed to the advantage of out-of-plane polarization for the generation and transport of carriers. This work suggests that 2D molecular ferroelectrics with out-of-plane polarization are potential candidates for the fabrication of photovoltaic devices.