Temperature-dependent Schottky barrier in high-performance organic solar cells

Area of Science:

• Materials Science
• Solid State Physics
• Organic Electronics

Background:

• Organic solar cells (OSCs) have achieved significant power conversion efficiencies (PCEs) around 10% due to material advancements.
• Understanding the fundamental physics of OSCs, particularly the role of the blend/cathode Schottky junction, is gaining traction.
• The blend/cathode Schottky junction is now recognized as the primary diode responsible for the photovoltaic function in bulk-heterojunction OSCs.

Purpose of the Study:

• To investigate the physical properties of the blend/cathode Schottky junction in organic solar cells.
• To analyze the temperature-dependent behavior of these junction diodes to understand their role in device performance.

Main Methods:

• Fabrication of organic solar cells using a PThBDTP:PC71BM blend, achieving PCEs over 10%.
• Temperature-dependent characterization of junction diodes from 70 K to 290 K.
• Utilized current-voltage, capacitance-voltage, and impedance spectroscopy measurements.

Main Results:

• The study revealed that the Schottky barrier height in the investigated OSCs exhibits considerable inhomogeneity.
• This inhomogeneity in Schottky barrier height was successfully modeled using two distinct sets of Gaussian distributions.
• The findings provide crucial insights into the charge transport mechanisms within the bulk-heterojunction active layer.

Conclusions:

• The blend/cathode Schottky junction's properties, particularly its inhomogeneous barrier height, are critical for organic solar cell performance.
• Understanding and potentially controlling this inhomogeneity could lead to further improvements in OSC efficiency.
• This research contributes to a deeper fundamental understanding of photovoltaic processes in organic electronic devices.