Layer-edge device of two-dimensional hybrid perovskites

Abstract

Two dimensional layered organic-inorganic hybrid perovskites (2D perovskites) are potential candidates for next generation photovoltaic device. Especially, the out-of-plane surface perpendicular to the superlattice plane of 2D perovskites (layer-edge surface) has presented several exotic behaviors, such as layer-edge states which are found to be crucial for improving the efficiency of 2D perovskite solar cells. However, fundamental research on transport properties of layer-edge surface is still absent. In this report, we observe the electronic and opto-electronic behavior in layer-edge device of 2D perovskites. The dark and photo currents are demonstrated to strongly depend on the crystallographic orientation in layer-edge device, and such anisotropic properties, together with photo response, are related to the thickness of inorganic layers. Finally, due to the abundant hydroxyl groups, water molecules are easy to condense on the layer-edge surface, and the conductance is extremely sensitive to the humidity environment, indicating a potential application of humidity sensor.

Fig. 1

Layer-edge device. a Schematic diagram of layer-edge surface of 2D perovskite (HOC₂H₄NH₃)₂PbI₄. Blue arrow and red arrow between electrodes indicate the direction of layer-edge 90° and 0°, respectively. b Top view of layer-edge surface. c Optical image of layer-edge surface device. The scale bar is 400 μm. d AFM image of layer-edge surface

Fig. 2

Transport properties of layer-edge device with n = 1. a I–V curve in dark and photo environment under white light with the power of 1 mW cm⁻². I_d is dark current and I_p is photo current for layer-edge 0° and 90° devices. b Photo responsivity vs wavelength. The light power density is 10 mW cm⁻². c Photo current vs photoexcitation density in layer-edge 0° and 90° devices. The bias voltage is fixed at 3 V in b and c

Fig. 3

Thickness-dependent electronic/opto-electronic properties. a Schematic image of 2D perovskites with n = 1, 2, 3, and ∞. Dark and photo current of 2D perovskite with b n = 2 and c n = 3. d Anisotropy of conductance and photo conductance with different n

Fig. 4

Thickness-dependent photo response. a Photo response and b recovery of normalized current in 2D perovskite with n = 1, 2, and 3 and 3D perovskite

Fig. 5

Humidity sensitivity. a Dark current in dry air and with 57% humidity air in 2D perovskite layer-edge 0° device. b Humidity sensitivity and response time for devices on layer-edge 0° surface with different n, in-plane surface in 2D perovskites with n = 1, and (110) surface in 3D perovskites. c Schematic diagram of water absorption in layer-edge surface of 2D perovskites