Decoding Trap States in Working 2D Perovskite Multi-Functional Devices.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Device Physics

Background:

• Hybrid organic-inorganic perovskites, like 4-fluorophenethylammonium lead iodide (F-PEAI), are promising 2D materials for opto-electronic applications due to their unique properties and stability.
• Device performance in these materials is significantly impacted by trap states, which are difficult to characterize under operating conditions, especially in multi-functional devices.
• Characterizing trap states in multi-functional devices (e.g., field-effect transistors, photodetectors, synaptic devices) is challenging due to the need for methods that can distinguish carrier types and trapping centers without compromising device functionality.

Purpose of the Study:

• To introduce threshold voltage transient spectroscopy (TVTS) as a universal, non-invasive method for probing trap states in 2D hybrid perovskite single-crystal devices.
• To demonstrate TVTS's capability for real-time extraction of sub-gap trap densities and energy distributions.
• To investigate the influence of trap states and dynamics on charge transport mechanisms in multi-functional 2D F-PEAI devices.

Main Methods:

• Development and application of threshold voltage transient spectroscopy (TVTS) for in situ defect spectroscopy.
• Utilizing 2D F-PEAI single-crystal field-effect transistors that also function as high-gain photodetectors.
• Performing measurements at various temperatures, including cryogenic conditions and above 100K, to study trap dynamics.

Main Results:

• TVTS successfully characterized trap states in fully processed 2D F-PEAI devices, providing real-time insights into trap densities and energy distributions.
• A transition in trap states was observed, from deep majority-carrier trapping at cryogenic temperatures to shallow trapping above 100K.
• Strong retrapping effects were found to enhance minority-carrier diffusion lengths (up to 5 µm) and device responsivities (up to 120 A/W).

Conclusions:

• TVTS is established as a powerful and versatile tool for in situ defect spectroscopy in multi-functional 2D perovskite devices.
• Understanding trap state dynamics is crucial for optimizing the performance of hybrid perovskite-based opto-electronic devices.
• The findings provide a pathway for enhancing the performance of 2D perovskite opto-electronic devices by managing trap states.