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Sub-millimetre light detection and ranging using perovskites

Abstract

Light detection and ranging (LiDAR) technology is an active remote-sensing system used in autonomous vehicles, machine vision and augmented reality. Improvements in the speed and signal-to-noise ratio of photodetectors are needed to meet these demanding ranging applications. Silicon electronics have been the principal option for LiDAR photodetectors in the range of 850–950 nm. However, its indirect bandgap leads to a low absorption coefficient in the near-infrared region, as well as a consequent trade-off between speed and efficiency. Here we report solution-processed lead–tin binary perovskite photodetectors that have an external quantum efficiency of 85% at 850 nm, dark current below 10–8 A cm–2 and response time faster than 100 ps. The devices are fabricated using self-limiting and self-reduced tin precursors that enable perovskite crystallization at the desired stoichiometry and prevent the formation of interfacial defects with the hole transport layer. The approach removes oxygen from the solution, converts Sn4+ to Sn2+ through comproportionation, and leaves neither metallic tin nor SnOx residues. To illustrate the potential of these solution-processed perovskite photodetectors in LiDAR, we show that they can resolve sub-millimetre distances with a typical 50 µm standard deviation.

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Fig. 1: Si and Pb–Sn photodetectors.
Fig. 2: Reducing strategy for Sn precursor.
Fig. 3: Performance of Pb–Sn photodetectors.
Fig. 4: Speed measurements for Pb–Sn devices.
Fig. 5: ToF measurements.

Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

This work was supported by the Natural Sciences and Engineering Research Council (NSERC) Alexander Graham Bell Canada Graduate Scholarships (CGS-D), Materials for Enhanced Energy Technologies (MEET) scholarships and the NSERC Collaborative Research and Training Experience (CREATE) program (grant no. 466083). F.P.G.A. acknowledges funding from CEX2019- 000910-S (MCIN/ AEI/10.13039/501100011033), Fundació Cellex, Fundació Mir-Puig, Generalitat de Catalunya through CERCA.

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Contributions

A.M.N., F.P.G.A. and E.H.S. conceived the idea and designed the experiments. M.W. contributed to the initial fabrication and speed measurements. A.M.N. and M.V. modelled the device performance and also fabricated the devices. M.V. measured the EQE and dark current of the device. A.M.N. performed the TPC measurement and LiDAR demo. T.Z. performed the theoretical calculation for SnOx energy level. E.H.S., S.H., M.I.S. and Y.H. provided advice. A.M.N., A.J., M.V., F.P.G.A. and E.H.S. composed the manuscript. All the authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Amin Morteza Najarian PhD or Edward H. Sargent.

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Nature Electronics thanks the anonymous reviewers for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Performance modeling of the photodetector.

Equations are provided in Methods section. a, Percentage of absorbed light vs. thickness at indicated absorption coefficients. EQE and bandwidth of b, Silicon and c, PbSn perovskite vs. film thickness. d, Comparison of silicon and PbSn perovskite from the last two panels. Parameters used for the modeling are given in Extended Data Fig. 2a.

Extended Data Fig. 2 Combined speed × efficiency characteristic of the photodetector.

a, Parameters used in the modeling of PbSn and Silicon photodetectors. b, Combined speed × efficiency modeling of silicon and PbSn PVK. c, Comparison between estimated performance and actual devices.

Extended Data Fig. 3 Performance of NiOx vs PEDOT:PSS HTL.

a, EQE comparison between PEDOT:PSS and NiOx using tin-powder reduced precursor (TPRP) strategy. b, Representative current density vs. voltage (JV curves) under the dark condition for the mentioned HTLs. Tin wire-reduced precursor strategy is used for all three shown cases. c, Comparison of dark current density at 50 mV for devices fabricated with PEDOT:PSS, NiOx, and without HTL with different Sn reducing strategy.

Extended Data Fig. 4 Possibility of interfacial SnOx formation.

a, Diagram comparing the formation energy of different form of oxide for Ni and Sn. Electrostatic potential (in eV) at the cores of oxygen atoms along the longitudinal direction of the b, DFT simulated structure of formed SnO layer on top of NiO HTL. c, NiO/SnO (001) and d, NiO/SnO2 (001) longitudinally lattice-matched supercell calculated by DFT-PBE within spin-polarized treatment for Ni. In each subplot, the top are the atomic structures of a (001)-oriented NiO/(SnO/SnO2) superlattice; Ni atoms are shown in grey, Sn atoms are purple, and O atoms are red. Schematic plots of the band alignment for e, NiO/SnO and f, NiO/SnO2 interface. The bandgap values are obtained according to a bulk calculation with HSE06 functional. g, Energy level diagram for different layers of fabricated devices, including SnO.

Extended Data Fig. 5 Citation for the data used in the manuscript.

a, Fig. 3a; b, Fig. 3b; c, Fig. 4c. The numbers shown in the Figure, refer to the raw number in Extended Data Tables 1 and 2.

Extended Data Fig. 6 Geometrical capacitance effect in photodetectors time response.

Measured fall time of the pixels is plotted vs. pixel area (mm2). The area for direct probe connection is estimated with the extension of the capacitance-limited regime. The area could be smaller than the estimated one. Area effect on response time of silicon photodetector is also compared with PbSn. Silicon below 0.1 mm2 reaches the plateau, and further decrease in the area does not decrease the response time. This behaviour indicates that the relatively poor carrier mobility limits the speed of Si PIN PDs.

Extended Data Fig. 7 Impedance measurement of the PbSn device.

a, Impedance plot measured in the dark under short-circuit conditions. b, Capacitance spectra obtained under the same condition as panel a. Black lines correspond to fits. c, Modified Randles equivalent circuit used for the fitting with Rs, Cg, and Cs related to series resistance, geometrical capacitance, and interface accumulation capacitance and R2 and R1 as surface recombination resistance. d, Parameters obtained by fitting the impedance data with Randles equivalent circuit.

Extended Data Fig. 8 Mapping of the distance using PbSn photodetector.

a, The input for the mirror’s position in the ToF setup shown in Fig. 5a for 105 individual measurements. The motorized stage controls the position of the mirror (distance in respect to the light source). The distance of zero is arbitrary, and it means that light is traveling the same distance as the reference pathway toward the InGaAs detector in the interferometer. b, Graph showing the response when the mirror has moved by 1.0, 3.0, 5.0, and 7.0 mm. For better visualization of peak positions, the response magnitude has multiplied by a power of 400. Averages and standard deviations of estimated depths based on the response time are shown on right side c, The output of the estimated distances using the peak position of PbSn photodetector response. The 3D visualization of these results is shown in Fig. 5d.

Extended Data Table 1 Comparison of the solution-processed photodetectors
Extended Data Table 2 Comparison of commercial silicon photodetector

Supplementary information

Supplementary Information

Supplementary Notes 1 and 2, Figs. 1–11 and Tables 1–4.

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Morteza Najarian, A., Vafaie, M., Johnston, A. et al. Sub-millimetre light detection and ranging using perovskites. Nat Electron 5, 511–518 (2022). https://doi.org/10.1038/s41928-022-00799-7

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