Anomalous Ambipolar Phototransistors Based on All‐Inorganic CsPbBr₃ Perovskite at Room Temperature

Abstract

Despite its extensive research in photovoltaics and light emitting diodes, the charge transport properties of all‐inorganic perovskite cesium lead bromide (CsPbBr3) remain elusive. Clarification of the intrinsic charge transport of this perovskite material is highly desirable, which will help to understand its working mechanism and fabricate high performance electronic devices. Here, it is demonstrated that the phototransistors based on CsPbBr3 microplates show anomalous ambipolar transport characteristics at room temperature. The hole mobility shows light dependence, while the electron mobility is identical under various light incidence. The hole mobility increases from 0.02 cm2 V−1 s−1 (in dark conditions) to 0.34 cm2 V−1 s−1 (50 mW cm−2); while the threshold voltage is shifted by 14 V when electron is the majority charge carrier. The anomalous transport behavior can be attributed to the photovoltaic and photoconductive effects. Moreover, the device shows photoresponsivity and detectivity up to 110 mA W−1 and 4.5 × 1013 Jones, respectively, under 532 nm laser illumination. This research unveils the charge transport mechanism of CsPbBr3 perovskite, provides more evidence and will thus contribute to the perovskite electronic and optoelectronic researches.

Charge Traps in All‐Inorganic CsPbBr3 Perovskite Nanowire Field‐Effect Phototransistors

“…[ 11 ] In other CsPbBr 3 systems higher FET mobilities with record values of up to 2.2 cm 2 V −1 s −1 at room temperature have been reported. [ 12,28,29,39 ] However, even these record mobilities are still at well below what has been expected from time‐resolved photoluminescence measurements, [ 7,40 ] acousto–optoelectronic spectroscopy, [ 41 ] Hall‐effect measurements, [ 36,42 ] and THz spectroscopy. [ 43 ] Thus, a better understanding of the underlying transport mechanisms bears great potential for optimizing mobilities of all‐inorganic perovskite devices.…”

“…This compares very well even to single crystal CsPbBr 3 samples with responsivities of up to several hundred A W −1 at comparable power densities. [ 7,8,12,47 ] The maximum specific detectivity in the shot‐noise limit [ 12 ] reaches values of ≈1 × 10 13 Jones at this power density. The gate dependence of both resistivity and detectivity is shown in Figure S4, Supporting Information.…”

“…[ 19,21 ] In this context it is very instructive to distinguish between shallow traps close to the band edge (Δ E ≈ k B T ) and deep traps far away from the band edge (Δ E ≫ k B T ). [ 21,49 ] First, we estimated the trap density of deep traps based on the subthreshold swing, S , of the transfer curves using the formulas [ 12,49,55 ] where e is the elementary charge, k B the Boltzmann constant, T the temperature, and C the gate dielectric capacitance per unit area. An illustration of the subthreshold swing determination is shown in Figure 2a.…”

“…This trap density is smaller than trap densities reported in literature even for single crystal samples. [ 12,22 ] As the Fermi level is still far away from the band edge in the subthreshold regime, the density N DT can be associated with deep trap states. [ 49 ] The density N ST of shallow trap states closer to the band edge can be estimated from the dependence of the threshold voltage on the temperature using [ 49,55 ] …”

“…Halide perovskite materials have emerged as a promising new class of semiconductor materials for optoelectronic applications owing to their attractive optical and electronic properties such as high absorption coefficients [ 1,2 ] and long charge carrier lifetime, [ 3 ] together with ease of fabrication, solution processability and low cost. [ 4 ] They have shown great promise and potential in various applications such as solar cells, [ 3,5 ] photodetectors, [ 6–8 ] field‐effect transistors (FETs), [ 9–12 ] and lasers. [ 13 ] However, the performance of halide perovskite devices is often limited by insufficient stability and moderate crystallinity.…”