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Low-energy room-temperature optical switching in mixed-dimensionality nanoscale perovskite heterojunctions

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Science Advances  28 Apr 2021:
Vol. 7, no. 18, eabf1959
DOI: 10.1126/sciadv.abf1959
  • Fig. 1 Ground- and excited-state charge transfer in bilayer NC/SWCNT heterojunctions.

    (A) Absorption spectra of a neat (6,5) s-SWCNT film, FAPbBr3 NC array, and a FAPbBr3 NC/SWCNT heterojunction. SWCNT optical transitions labeled as Sxx for excitonic transitions and X+ for positively charged trion absorption. Absorption spectra of other NC/SWCNT heterojunctions shown in fig. S2. (B) FET transfer curves for FAPbBr3 NC/SWCNT heterojunctions (left) in the dark or illuminated with a white LED or 532-nm laser (VDS = 3 V). FET curves for other NC/SWCNT heterojunctions shown in fig. S4. FET transfer curves for neat (6,5) s-SWCNT thin films (right) that are undoped (light gray line), lightly p-doped with a one-electron oxidant (triethyloxonium hexachloroantimonate or OA, darker gray line), or heavily doped with OA (black line, p+). All SWCNT transfer curves measured in the dark, VDS = 3 V. (C) Time-resolved PL (TRPL) decay of the FAPbBr3 545-nm emission for a neat FAPbBr3 NC array (dashed line) and a FAPbBr3 NC/(6,5) s-SWCNT heterojunction (solid line). Inset shows PL spectra for the same two samples. Excitation at 405 nm. PL and TRPL for other NC/SWCNT heterojunctions shown in fig. S8. (D) Energetics estimated for (6,5) s-SWCNT thin film and FAPbBr3 NC array, showing work functions (ϕi), electron affinities (χi), and electronic band gaps (Egi) of the separate films (before contact). The ultraviolet photoelectron spectroscopy (UPS) data and analysis are shown in fig. S9 for FAPbBr3 NCs. Values for SWCNTs taken from our recent UPS measurements (39) and separate calculations (62) (upper and lower bounds on gray boxes, respectively). (E) Schematic of the FET setup used. The blow-up highlights the NC/s-SWCNT interface and the photoinduced hole transfer event that occurs at this interface to drive the photocurrent observed in phototransistors. Micrographs of typical FET channel shown in fig. S10.

  • Fig. 2 High responsivity and transient photoresponse in NC/SWCNT heterojunctions.

    (A) Photoresponsivity (Rλ) as a function of incident fluence (continuous excitation) with either 405- or 532-nm laser. Excitation wavelength and bias conditions listed in legend. (B) Photocurrent (Iph) as a function of time, VGS, and photoexcitation with a 405-nm laser. Green region highlights the photocurrent rise time during continuous illumination, and orange region highlights the photocurrent decay time after the illumination is turned off. VGS = 0 V and VDS = 0.1 V. Inset shows the same experiment performed on a bulk FAPbBr3/(6,5) sample. VGS = 0 V and VDS = 3 V. (C) Stimulation of PPC in the three NC/SWCNT bilayers with 5-s, 405-nm light pulse. Inset shows that the CsPbBr3 and FAPbBr3 heterojunction photocurrent transients last well beyond an hour.

  • Fig. 3 Tracking PPC and ion migration in NC/SWCNT heterojunctions.

    (A) Time-dependent static absorption spectra in the near-infrared region (highlighting changes to S11 and X+ peaks) for unilluminated FAPbBr3 NC/SWCNT heterojunction, after 40 min of continuous 405-nm illumination, and after the 405-nm illumination is ceased (after 40-min illumination) for 35 min. Inset shows the temporal changes to the s-SWCNT S11 area during the continuous illumination phase (green region) and after the illumination is turned off (orange region). (B) Slow growth of 9-GHz conductance during continuous illumination (green region) and slow decay (orange region) after 532-nm laser is turned off. (C) Normalized surface bromine concentration, as measured by TOF-SIMS, for a FAPbBr3 NC array and a FAPbBr3/(6,5) heterojunction, as a function of continuous illumination time with a 405-nm laser. (D) Temperature-dependent photocurrent decay transients of FAPbBr3/(6,5) heterojunction, photoexcited at 405 nm for 5 s with a fluence of 18 mW/cm2. VGS = 0 V and VDS = 0.1 V. Inset shows the dependence of the photocurrent at 400 s [Iph (400 s)] as a function of temperature. (E and F) Schematics of field-induced bromine vacancy (VBr) ion migration during illumination (E) and slower ion diffusion when light is turned off (F).

  • Fig. 4 Basic synapse-like functions with NC/SWCNT phototransistors.

    (A) Dependence of photocurrent for FAPbBr3 NC/SWCNT phototransistor as a function of gate voltage (VGS), source-drain voltage (VDS), and the energy per 30-μs 405-nm pulse. (B) Writing and erasing photocurrent in NC/SWCNT phototransistors at low applied bias (steady-state biases of VGS = 0 V and VDS = 0.1 V). Main plot shows Iph for the three photoexcited NC/SWCNT phototransistors under conditions of identical photon fluence (photons cm−2 s−1) within pulses with varying pulse width. Ten seconds after each light pulse writes a photocurrent, the photocurrent is erased with a 300-ms gate voltage pulse (VGS = +20 V). Inset shows Iph as a function of pulse width for the three phototransistors. (C) Comparison of FAPbBr3 NC/SWCNT phototransistor that is potentiated with a 300-μs 405-nm pulse and either left to decay naturally (dashed line) or electrically habituated with five consecutive VGS = +10 V, 300-ms gate pulses. Steady-state biases of VGS = 0 V and VDS = 0.1 V. (D) Photocurrent in FAPbBr3 NC/SWCNT heterojunction phototransistor as a function of pulse number for four consecutive 30-μs 405-nm pulses delivered at different frequencies. Inset shows the frequency-dependent SFPD index, calculated as the percentage increase in photocurrent measured after the fourth pulse compared to the photocurrent measured after the first pulse. Steady-state biases of VGS = 0 V and VDS = 0.1 V. (E) Photocurrent in FAPbBr3 NC/SWCNT heterojunction phototransistor as a function of time for 30-μs 405-nm pulses delivered at different frequencies. Inset shows the frequency-dependent Iph measured at 10 s after initiation of the pulse train. Steady-state biases of VGS = 0 V and VDS = 0.1 V.

  • Fig. 5 Short-channel NC/SWCNT optical synapses.

    (A) Optical micrograph of finished short-channel FETs with eight different devices. Channel width of all devices is 1 μm, shown by the white box (not to scale), and channel lengths are listed on the left of the image. (B) Cartoon schematic of aligned s-SWCNTs across the source-drain channel. (C) Forward scan transfer curve for (6,5) s-SWCNT FET in the dark. (D) Photocurrent initiated in a FAPbBr3 NC/SWCNT short-channel (Lch = 150 nm) phototransistor by a 2-s white light pulse. VDS = 0.1 V and VGS = 0 V. (E) Photocurrent delivered by short 405-nm laser pulses (tpulse = 1, 2, and 3 ms) for short-channel NC/SWCNT optical synapses with Lch = 100, 200, and 300 nm. VDS = 0.1 V and VGS = 0 V. Inset shows the dependence of the induced Iph on the pulse width for each heterojunction.

Supplementary Materials

  • Supplementary Materials

    Low-energy room-temperature optical switching in mixed-dimensionality nanoscale perovskite heterojunctions

    Ji Hao, Young-Hoon Kim, Severin N. Habisreutinger, Steven P. Harvey, Elisa M. Miller, Sean M. Foradori, Michael S. Arnold, Zhaoning Song, Yanfa Yan, Joseph M. Luther, Jeffrey L. Blackburn

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