Ambipolar Solution-processed Hybrid Perovskite Phototransistors (1502.03995v3)

Abstract: Organolead halide perovskites have attracted substantial attention due to their excellent physical properties, which enable them to serve as the active material in emerging hybrid solid-state solar cells. Here we investigate the phototransistors based on hybrid perovskite films, and provide direct evidence for their superior carrier transport property with ambipolar characteristics. The field-effect mobilities for triiodide perovskites at room temperature are measured as 0.18 (0.17) cm2 V-1 s-1 for holes (electrons), which increase to 1.24 (1.01) cm2 V-1 s-1 for mixed halide perovskites. The photoresponsivity of our hybrid perovskite devices reaches 320 A W-1, which is among the largest values reported for phototransistors. Importantly, the phototransistors exhibit an ultrafast photoresponse speed of less than 10 {\mu}s. The solution-based process and excellent device performance strongly underscore hybrid perovskites as promising material candidates for photoelectronic applications.

• The paper demonstrates ambipolar carrier transport in hybrid perovskite phototransistors, achieving balanced p-type and n-type conduction.
• It reports enhanced field-effect mobilities, with CH₃NH₃PbI₃ values around 0.18 cm²/V·s rising to over 1 cm²/V·s in doped variants.
• The devices exhibit high photoresponsivity (320 A/W) and ultrafast response (<10 µs), with low dark current and improved stability from a PMMA coating.

Overview of Ambipolar Solution-Processed Hybrid Perovskite Phototransistors

This paper investigates the fabrication and characterization of ambipolar phototransistors based on solution-processed hybrid perovskite films. The authors focus on organolead halide perovskites, particularly methylammonium lead iodide (CH₃NH₃PbI₃) and mixed halide perovskites (CH₃NH₃PbI₃₋ₓClₓ), exploring their potential use in high-performance photoelectronic devices. Key properties such as carrier mobility, photoresponsivity, and response speed are examined, highlighting the advantages and potential applications of these materials in optoelectronic devices.

Key Findings

1. Ambipolar Carrier Transport: The authors present evidence of ambipolar carrier transport in the studied perovskite phototransistors. They demonstrate that the devices exhibit balanced p-type and n-type characteristics, which is crucial for developing efficient optoelectronic components.
2. Field-Effect Mobility: The paper reports enhanced field-effect mobilities for perovskite phototransistors. For instance, the mobility values for CH₃NH₃PbI₃ were found to be 0.18 cm²/V·s for holes and 0.17 cm²/V·s for electrons, with a substantial increase to 1.24 cm²/V·s (holes) and 1.01 cm²/V·s (electrons) in the doped variant CH₃NH₃PbI₃₋ₓClₓ.
3. Photoresponsivity and Response Speed: The devices achieved a high photoresponsivity of 320 A/W alongside an ultrafast photoresponse speed of less than 10 µs. These results position perovskite phototransistors as favorable candidates for fast and responsive optoelectronic devices.
4. Dark Current Suppression: The paper emphasizes the low dark current levels of the devices, a significant factor contributing to their high photoresponsivity. The suppression of dark current is notably effective in the undoped CH₃NH₃PbI₃ channels, which leads to better phototransistor performance.
5. Protective Coating for Stability: To enhance the stability of the devices, a protective layer of poly(methyl methacrylate) (PMMA) was applied, improving the phototransistors' resistance to environmental factors such as moisture and oxygen.

Implications and Future Work

The findings presented in this paper imply significant potential for the use of hybrid perovskite materials in high-performance phototransistors and other photoelectronic applications such as photosensors and light-activated switches. The solution-based processing method offers a cost-effective and scalable approach for device fabrication, which could be advantageous for large-scale production.

The ambipolar characteristics and high mobility of these perovskite materials provide a strong foundation for further developments in ambipolar transistor technologies. The promising results on photoresponsivity and response speed indicate that future research could focus on optimizing these attributes through strategic material modifications and innovative device architectures.

Additionally, the performance of perovskite phototransistors can potentially be improved by reducing channel lengths, thereby decreasing carrier transit times and enhancing mobility. Exploring doping strategies and honing fabrication techniques might also yield improvements in the optoelectronic properties of these devices.

In conclusion, the paper underscores the relevance of hybrid perovskites as promising materials for advancing the field of optoelectronics. The elucidation of their properties and performance metrics in phototransistors paves the way for future innovations and reinforces their applicability across diverse engineered systems.