Articles

1. Abstract

  • Perovskite Photodetectors (PPDs): Gaining interest due to unique material properties.

  • Challenge: Electrons and holes transport layers (ETLs and HTLs) add complexity and reduce reliability.

  • Proposed Solution: Employing a carrier transport layer (CTL)-free perovskite homojunction.

  • Design Simulation: Conducted using Silvaco TCAD simulator, investigating the impact of various parameters on PPD characteristics.

  • Key Findings:

    • Optimum Detectivity: 7.4 × 10^13 Jones at 750 nm.

    • Optimum Responsivity: 0.42 A/W at 675 nm.

    • Optimum External Quantum Efficiency (EQE): 84 % at 475 nm.

  • Conclusion: p-n homojunction design is promising for high-performance PPDs.

2. Introduction

  • Importance of Photodetectors: Convert light to electrical signals, critical in diverse fields (e.g., imaging, sensing).

  • Current Focus: Organic-inorganic hybrid perovskite photodetectors praised for long carrier diffusion length and high absorption coefficient.

  • Configurations: Mainly lateral (phototransistor/photoconductor) and vertical structures (photodiode).

  • Vertical Photodiodes: Fast response, low voltage, large detectivity, typically utilize sandwich structures with ETLs and HTLs.

  • Issues: Complex fabrication of layers and their effect on lifetime and reliability necessitates simpler designs.

  • Proposed Approach: Utilize self-doping of perovskite material (MAI for p-type, PbI2 for n-type) to create p-n homojunctions.

3. Methodology

  • Simulation Framework: Utilized Silvaco TCAD to model CTL-free homojunction PPDs.

  • Device Structure:

    • Layer Composition: Au/p-CH3NH3PbI3/n-CH3NH3PbI3/FTO.

    • Functional Mechanism: Electric field drives carrier transport and reduces recombination.

    • Effective area and illumination specifications defined for simulation accuracy.

  • Performance Metrics: Responsivity, detectivity, EQE analyzed through mathematical equations including:

    1. EQE = Iphhv / Pe

    2. Responsivity (R) = Iph / P

    3. Detectivity (D)* = R / (2eJdark).

4. Results and Discussion

4.1 Influence of Doping Density

  • Doping Impact: Variations in doping levels directly relate to electric field strength.

  • Peak Responsivity found optimal at

    • p-perovskite (NA): 5 × 10^17 cm-3.

    • n-perovskite (ND): 5 × 10^14 cm-3.

  • Increasing ND reduces effectiveness due to weak electric field strength, affecting carrier separation and increasing recombination.

4.2 Influence of Layer Thickness

  • N-Perovskite Thickness Effect: Thicker layers enhance EQE at long wavelengths while causing short wavelength losses at thicknesses beyond 600 nm.

  • P-Perovskite Thickness: Beyond 100 nm, EQE and responsivity plateau due to saturation in absorptive capacity of n-perovskite.

4.3 Influence of Carrier Mobility

  • Mobility's Role: Higher n-perovskite mobility significantly enhances detectivity and responsivity.

  • Low Mobility Impact: Less impact observed from changes in p-perovskite mobility since most carriers primarily exist in n-perovskite.

  • Recommended Minimum Mobilities: P-perovskite >= 10 cm2/V/s, N-perovskite >= 1 cm2/V/s.

5. Conclusion

  • Summary of Findings: Numerical design validated that CTL-free homojunction PPDs can achieve high performance.

  • Optimal Configurations:

    • Densities: p-perovskite at 5 × 10^17 cm-3 and n-perovskite at 5 × 10^14 cm-3.

    • Thickness: p-perovskite at 100 nm, n-perovskite at 600 nm.

  • Performance Excellence: Wide detection spectrum (350-800 nm) confirmed efficient carrier transport leading to high EQE, responsivity, and detectivity.