Mobility dependent recombination models for organic solar cells

Area of Science:

• Materials Science
• Physical Chemistry
• Renewable Energy

Background:

• Charge carrier recombination is a key factor limiting power conversion efficiency in solar cells.
• In organic semiconductors, low charge carrier mobilities lead to recombination rates dependent on mobility, unlike inorganic cells.
• The Langevin recombination model, developed for gas-phase ions, has been applied to organic semiconductors but often overestimates recombination rates.

Purpose of the Study:

• To review the evolution of mobility-limited recombination models for organic solar cells.
• To explain discrepancies between the Langevin model predictions and experimental observations in organic solar cells.
• To discuss factors influencing charge carrier encounter probability and recombination rates in organic semiconductors.

Main Methods:

• Literature review of recombination models in organic solar cells.
• Analysis of the Langevin recombination theory and its limitations.
• Discussion of experimental findings and extended models for organic solar cells.

Main Results:

• Organic solar cell recombination is strongly dependent on charge carrier mobilities due to Coulomb attraction.
• The classical Langevin model often fails to predict observed recombination rates in organic devices.
• Factors like morphology, trapping, and electrode selectivity can reduce charge carrier encounter probability, leading to lower recombination rates.

Conclusions:

• Advanced models are needed to accurately describe charge carrier recombination in organic solar cells.
• Understanding mobility-limited recombination is crucial for improving organic solar cell performance.
• Further research into material properties and device architecture is necessary to overcome recombination limitations.