Magnetic and Electric Field Dependent Charge Transfer in Perovskite/Graphene Field Effect Transistors

Abstract

unique and outstanding optical properties such as high quantum yield (QY), strong absorption, and widely tunable band gap energy [8][9][10] accompanied by inexpensive solution processing techniques. [11][12][13] These PNCs have been successfully used in photon detectors operational in the visible wavelength range with photoresponsivity, R > 10 5 A W −1 , [14,15] and could offer further opportunities for UV applications. [16,17] Amongst device structures of particular interest are hybrid field effect transistors (FETs) that combine single-layer graphene (SLG) with PNCs. The performance of these devices, such as their response time, is affected by the slow, >1 s, redistribution of charge between the graphene layer and PNCs under light and/or electrostatic gating, [18,19] leading to the accumulation of a large amount of charge in the PNCs (7 × 10 12 cm −2 [19] ). This phenomenon can induce a range of interesting physical phenomena, such as an optically induced Stark effect, [20] large hysteresis on the gate voltage dependence of the graphene resistance, [19] and enhancement of the photoresponsivity. [21,22] However, to fully exploit the potential of perovskite/graphene structures, a comprehensive understanding of their properties is still needed. High magnetic fields are invaluable for interrogating fundamental physical processes Stable all-inorganic CsPbX 3 perovskite nanocrystals (PNCs) with high optical yield can be used in combination with graphene as photon sensors with high responsivity (up to 10 6 A W −1 ) in the VIS-UV range. The performance of these perovskite/graphene field effect transistors (FET) is mediated by charge transfer processes at the perovskite -graphene interface. Here, the effects of high electric (up to 3000 kV cm −1 ) and magnetic (up to 60 T) fields applied perpendicular to the graphene plane on the charge transfer are reported. The authors demonstrate electric-and magnetic-field dependent charge transfer and a slow (>100 s) charge dynamics. Magneto-transport experiments in constant (≈0.005 T s −1 ) and pulsed (≈1000 T s −1 ) magnetic fields reveal pronounced hysteresis effects in the transfer characteristics of the FET. A magnetic time is used to explain and model differences in device behavior under fast (pulsed) and slowly (continuous) changing magnetic fields. The understanding of the dynamics of the charge transfer in perovskite/graphene heterostructures developed here is relevant for exploitation of these hybrid systems in electronics and optoelectronics, including ultrasensitive photon detectors and FETs for metrology.

Photosensitisation of inkjet printed graphene with stable all-inorganic perovskite nanocrystals

“…S5†), which is likely due to the charge trapping on NC surface defects and slow charge dynamic. 29 For both devices, the relationship between incident light power, P , and the responsivity, R , follows R ∼ P −0.7 (Fig. 2c), similar to the R ( P ) previously reported for SLG decorated with CsPbI 3 NCs.…”

“…The observed hysteresis of the ρ ( V g ) dependence is due to slow charging of the perovskite NCs. 2,29 This was accompanied by a shift of the position of the Dirac point from +11 V to 0 V, thus indicating n-type doping of the SLG by CsPb(Br/I) 3 NCs. Similar n-type doping of SLG has previously been observed on SLG functionalised with CsPbI 3 NCs, due to the donor nature of CsPbX 3 NCs.…”

“…After illumination, the electrical properties of the devices recover to ~ 90% of the original value in about a minute, however the full recovery can take up to several hours for large incident illumination powers (see Supplementary Information, SI3, Figure S5), which is likely due to the charge trapping on NC surface defects and slow charge dynamic. 29 For both devices, the relationship between incident light power, P, and the responsivity, R, follows R ~ P -0.7 𝜏 𝑓𝑎𝑙𝑙 ~ 6 s (see Supplementary Information, SI3, Figure S5). The difference in photoresponsivity of the photodetectors decorated with different perovskite NCs is due to the NC composition, which affects their absorption (Figure 1d) and energy level alignment with SLG for charge transfer (inset in Figure 2c).…”

“…Similar n-type doping of SLG has previously been observed on SLG functionalised with CsPbI 3 NCs, due to the donor nature of CsPbX 3 NCs. 2 The electron and hole field-effect mobilities of the SLG device before NC deposition were calculated at the point of the highest slope of σ(V g ) (highest value of μ FE ) for both electrons and holes using the method reported in 29,30 (see Methods section). For pristine SLG, μ e = 0.70 m 2 V −1 •s −1 and μ h = 0.55 m 2 V −1 •s −1 , respectively.…”

“…The electron and hole field-effect mobilities of the SLG device before NC deposition were calculated at the point of the highest slope of σ ( V g ) (highest value of μ FE ) for both electrons and holes using the method reported in 29,30 (see Methods section). For pristine SLG, μ e = 0.70 m 2 V −1 ·s −1 and μ h = 0.55 m 2 V −1 ·s −1 , respectively.…”