Detecting trap states in planar PbS colloidal quantum dot solar cells

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Colloidal quantum dot photovoltaics (QDPVs) show promise for efficient solar energy conversion.
• Planar QDPV architectures have improved power conversion efficiency.
• Performance limitations in QDPVs are often attributed to trap states within the active layer.

Purpose of the Study:

• To characterize trap states in planar PbS QDPVs (ITO/ZnO/PbS-TBAI/PbS-EDT/Au).
• To understand the role of these trap states in limiting device performance.
• To provide insights for developing strategies to enhance QDPV efficiency.

Main Methods:

• Impedance spectroscopy was employed to detect and quantify trap states.
• Temperature-dependent open-circuit voltage analysis was performed.
• Temperature-dependent diode property and build-in potential analyses were conducted.

Main Results:

• A trap state was identified approximately 0.34 eV below the conduction band.
• The density of these trap states was determined to be around 3.2 × 10^16 cm⁻³ eV⁻¹.
• Below-bandgap activation energies were consistently found to be between 1.17-1.20 eV.

Conclusions:

• Trap states significantly impact the performance of planar PbS QDPVs.
• Understanding and mitigating these trap states is crucial for advancing QDPV technology.
• The identified trap characteristics provide a basis for targeted material engineering and device optimization.