High‑Performance All‑Perovskite Photodetector Delivering Ultrafast Response

Abstract

Perovskite materials combine exceptional optoelectronic properties with a facile solution‑processing route, making them ideal for next‑generation photodetectors. We report a hybrid perovskite photodetector comprising a CH₃NH₃PbI_3‑xCl_x depletion layer and a sensitizing layer of CsPbBr₃ quantum dots (QDs). Operated in the visible spectrum, the device delivers a record responsivity of 0.39 A W^‑1, a detectivity of 5.43 × 10⁹ Jones, ambipolar carrier mobilities of 172 cm² V^‑1 s^‑1 (holes) and 216 cm² V^‑1 s^‑1 (electrons), and ultrafast response times (rise 121 µs, fall 107 µs). These metrics position the CH₃NH₃PbI_3‑xCl_x-CsPbBr₃ heterostructure as a promising platform for high‑performance photoelectronic applications.

Background

Photodetectors (PDs) are central to optical imaging, environmental monitoring, telecommunications, and remote sensing. Among the device architectures—photodiodes, photoconductors, and photo‑field‑effect transistors (photo‑FETs)—photo‑FETs uniquely balance high gain with low dark current, owing to their gate‑controlled depletion channel. However, thin active layers that enable efficient gate tuning often suffer from reduced photon absorption, limiting sensitivity. Thus, the choice of high‑photo‑electric‑conversion‑efficiency (PECE) materials is critical.

Halide perovskites have emerged as leading candidates for photoactive layers due to their strong absorption, high power‑conversion efficiencies, and scalable processing. Recent studies have integrated perovskites into photo‑FETs, yet the challenge remains to achieve both high gain and low dark current in a single device. One effective strategy is to sensitize the perovskite channel with a high‑absorption material, decoupling optical absorption from charge transport. Quantum dots (QDs) such as PbSe, PbS, and CdSe have proven effective, and the newer perovskite QDs (CsPbX₃, X = Cl, Br, I) offer superior absorption and facile synthesis.

We therefore explore a fully perovskite architecture: a CH₃NH₃PbI_3‑xCl_x channel decorated with CsPbBr₃ QDs. This design promises enhanced responsivity and detectivity while maintaining fast response times, as demonstrated in the following sections.

Materials and Methods

Device Fabrication

Device fabrication begins with a commercial n⁺ Si wafer capped with a 300‑nm SiO₂ dielectric (capacitance C_ox = 11.5 nF cm^‑2). A CH₃NH₃PbI_3‑xCl_x perovskite film (≈102 nm) is spin‑coated from a DMF solution and post‑annealed for 90 min. Subsequently, three successive spin‑coats of CsPbBr₃ QDs (≈97 nm total) are deposited at 1500 rpm, with 15‑min drying at 60 °C after each coat. Source and drain electrodes (Au) are thermally evaporated through a shadow mask, yielding a channel length of 0.1 mm and width of 2.5 mm.

Materials

The precursor solutions contain DMF (99.5 %), oleic acid (90 %), oleylamine (90 %), PbCl₂ (99.99 %), PbBr₂ (99 %), and CH₃NH₃I (98 %). Full synthesis protocols for the perovskite and CsPbBr₃ QDs, along with instrument details, are provided in Supplementary File 1.

Results and Discussion

Figure 1a illustrates the device architecture: a gate electrode, SiO₂ dielectric, CH₃NH₃PbI_3‑xCl_x channel, CsPbBr₃ QD sensitizer, and Au source/drain contacts. SEM cross‑section (Fig. 1b) confirms layer thicknesses (102 nm perovskite, 97 nm QDs) and a clean interface without interfacial layers, essential for efficient charge transfer.

The perovskite film exhibits a high‑crystallinity orthorhombic structure, as shown by XRD peaks at 14.2°, 28.6°, 31.0°, and 43.4° (Fig. 1d). TEM imaging of the CsPbBr₃ QDs (Fig. 1c) reveals uniform, rectangular particles with a cubic lattice (JCPDS 54‑0752). Optical absorption measurements (Fig. 1e) demonstrate that the QD layer enhances absorption in the 400–500 nm range, increasing the overall photo‑absorption of the device. The QD bandgap, calculated via the Tauc plot, is 2.38 eV, matching the PL peak.

Electrical characterization (Fig. 2a) shows two distinct regimes: in the OFF state (|V_GS| = 0) the device behaves like a Schottky diode, while in the ON state (|V_GS| ≥ 0.4 V) conventional FET characteristics emerge, indicating effective depletion control. Transfer curves (Fig. 2b) reveal ambipolar behavior: negative V_GS drives hole‑enhanced conduction, positive V_GS induces electron‑enhanced conduction. The field‑effect mobilities extracted from the linear region (µ = L V_DS C_ox W ∂I_DS/∂V_GS) are 172 cm² V^‑1 s^‑1 (p‑type) and 216 cm² V^‑1 s^‑1 (n‑type), confirming balanced carrier transport.

Under 405 nm illumination, the device’s responsivity peaks at 0.39 A W^‑1 (Fig. 3a), surpassing the undoped perovskite counterpart (0.22 A W^‑1). Detectivity reaches 5.43 × 10⁹ Jones (Fig. 3b), outperforming the CPD (1.25 × 10⁹ Jones). Calculated noise‑equivalent power (NEP) is 9.21 × 10^‑12 W Hz^‑½, and the photoconductive gain is 1.197, underscoring the device’s sensitivity.

Temporal response tests (Fig. 4) show rise and fall times of 121 µs and 107 µs, respectively, when excited with a 4000 Hz pulsed laser at 648 mW cm^‑2. This ultrafast performance is attributed to efficient carrier separation at the perovskite/QD heterojunction and minimal recombination pathways.

The band alignment (Fig. 5) illustrates that the higher Fermi level of CsPbBr₃ drives electrons into the CH₃NH₃PbI_3‑xCl_x channel while holes are extracted into the QDs, promoting rapid charge extraction and enhancing responsivity.

Conclusion

We have fabricated a high‑sensitivity, all‑perovskite photodetector that integrates a CH₃NH₃PbI_3‑xCl_x channel with a CsPbBr₃ QD sensitizer. The device achieves a responsivity of 0.39 A W^‑1, detectivity of 5.43 × 10⁹ Jones, and carrier mobilities of 172 cm² V^‑1 s^‑1 (holes) and 216 cm² V^‑1 s^‑1 (electrons). Its rise/fall times of 121 µs/107 µs demonstrate ultrafast response, making it suitable for high‑speed optical applications. Future work will focus on reducing electrode spacing to enhance carrier collection and improving device longevity by optimizing ligand chemistry.

Availability of Data and Materials

The conclusions presented are supported by the data and figures included in this article.

Abbreviations

PDs

Photodetectors

CPD

CH₃NH₃PbI_3‑xCl_x perovskite photodetector

CCPD

CH₃NH₃PbI_3‑xCl_x-CsPbBr₃ photodetector

QDs

Quantum dots

FETs

Field‑effect transistors

TEM

Transmission electron microscopy

SEM

Scanning electron microscopy

XRD

X‑ray diffraction

NEP

Noise equivalent power

G

Gain