Exploration of sub-bandgap states in 2D halide perovskite single-crystal photodetector

Abstract

Greater stability of low-dimensional halide perovskites as opposed to their three-dimensional counterparts, alongside their high extinction coefficient and thus excellent emission properties, have made them popular candidates for optoelectronic applications. Topological edges are found in two-dimensional perovskites that show distinct electronic properties. In this work, using Kelvin Probe Force Microscopy, performed on butylammonium lead bromide (BA2PbBr4) single crystals with optical bandgap of ~413 nm, we elucidate the electronic response of the edges and their potential impact on photodetector devices. We show that the charge-carriers are accumulated at the edges, increasing with the edge height. Wavelength-dependent surface photovoltage (SPV) measurements reveal that multiple sub-bandgap states exist in BA2PbBr4. As the edge height increases, the SPV amplitude at the edges reduces slightly more as compared to the adjacent regions, known as terraces, indicating relatively less reduction in band-bending at the surface due possibly to increased de-population of electrons from sub-bandgap states in the upper bandgap half. The existence of sub-bandgap states is further confirmed by the observation of below-bandgap emission (absorption) peaks characterised by spectral photoluminescence and photothermal deflection spectroscopy measurements. Finally, we fabricated a photodetector using a millimetre size BA2PbBr4 single crystal. Noticeable broadband photodetection response was observed in the sub-bandgap regions under green and red illumination, which is attributed to the existence of sub-bandgap states. Our observations suggest edge-height dependence of charge-carrier behaviour in BA2PbBr4 single crystals, a potential pathway that can be exploited for efficient broadband photodetector fabrication.

Pin hole free 2D Ruddlesden-Popper Perovskite layer with closed packed large crystalline grains, suitable for fast response and high sensitive MSM photodetection

“…Figure S2 shows the I-V characteristics of the fabricated Au/RPP/Au photodetector at the dark and green-illumination conditions. The measured linear I-V characteristics reveal an ohmic contact between Au and RPP layer that is in agreement with the relating previous reports [7,[27][28][29][30][51][52][53]. On the other hand, the measured high dark current diminishes the detectivity for the realized Au/RPP/Au photodetector.…”

FACILE AND CONTROLLED SYNTHESIS OF 2D ORGANOMETAL HALIDE PEROVSKITE PURE BA2MAPb2I7 AND HETEROSTRUCTURED BA2PbI4/BA2MAPb2I7 SINGLE CRYSTALS

“…Owing to the same situation, similar results were observed for the BA 2 PbI 4 and BA 2 PbI 4 /BA 2 MAPb 2 I 7 perovskites, as shown in Figure 2 reported that high intensity XRD peaks of BA2MAPb2I7 crystals were obtained at the angles of 5.09°, 9.62°, 14.12°, 18.65°, 23.23°, 27.80° and 32.44° [33]. In addition, due to the continuity of the inorganic-organic-inorganic layer in the crystal structure of 2D OHP single crystals, the angle values at which XRD peaks increase regularly according to the d gap distance between the crystal planes [34][35][36]. Accordingly, the distance between the crystal planes of the synthesized 2D OHP single crystals was measured to be d=1.964nm and, using the Bragg equation (n𝜆 = 2𝑑𝑠𝑖𝑛𝜃), it was calculated that the difference between the angle values between each peak should be approximately 2𝜃=4.5°, which is consistent with the obtained results.…”

Navigating the Site-Distinct Energy Conversion Properties of Perovskite Quantum Wells

“…Such non-trivial electrical properties were attributed to a higher Fermi level of the terrace edges than the terraces, which renders a band bending at the terrace edges to accumulate the electrons . Later, such band bending and charge accumulation were also confirmed by Choi et al . The band bending at the terrace was visualized by the contact potential difference (CPD) characterization (Figure d,e).…”

“…E V is the valence band edge. Reproduced with permission from ref . Published by Springer Nature 2022.…”

“…Such non-trivial electrical properties were attributed to a higher Fermi level of the terrace edges than the terraces, which renders a band bending at the terrace edges to accumulate the electrons. 147 Later, such band bending and charge accumulation were also confirmed by Choi et al 145 The band bending at the terrace was visualized by the contact potential difference (CPD) characterization (Figure 15d,e). Holes rather than electrons were found to be the accumulating charges (Figure 15f), which hints at an electrical tunability of the terrace edges, as the situation is contrary to that in Wang's report.…”