Charge Carrier Dynamics at the Perovskite Interface with Self-Assembled Monolayers

Area of Science:

• Materials Science
• Photovoltaics
• Surface Chemistry

Background:

• Self-assembled monolayers (SAMs) are increasingly used in perovskite solar cells (PSCs) as alternatives to traditional hole transporting layers.
• The precise mechanisms governing SAMs' influence on interfacial electronic processes and charge dynamics remain unclear.
• Understanding these mechanisms is crucial for enhancing PSC efficiency and stability.

Purpose of the Study:

• To investigate the photocurrent and photovoltage dynamics at the perovskite/hole-collecting electrode interface.
• To elucidate the role of molecular properties of SAMs in controlling charge extraction and recombination.
• To develop a model explaining the impact of SAMs on interfacial processes in simplified perovskite solar cell structures.

Main Methods:

• Fabrication of a simplified perovskite solar cell with blocked electron extraction.
• Investigation of photoluminescence and photovoltage dynamics using short laser pulse excitation.
• Analysis of photocurrent dynamics considering charge carrier displacement, transport, trapping, and recombination.
• Development of a model incorporating molecular dipole moments and ionization potentials.

Main Results:

• Photovoltage dynamics are significantly influenced by the properties of transport layers and perovskite, varying with sample preparation.
• Photocurrent dynamics involve charge carrier displacement, hole transport, interface trapping, and electron-hole recombination.
• A model was proposed to explain the varying effects of different SAMs on hole extraction and recombination based on molecular properties.
• Long-lasting memory effects in photovoltage dynamics were observed, attributed to ion redistribution.

Conclusions:

• SAM properties critically affect interfacial electronic processes and photocurrent dynamics in perovskite solar cells.
• The proposed model provides insights into how molecular characteristics of SAMs influence charge transfer and recombination.
• Ion redistribution plays a significant role in the observed photovoltage memory effects, impacting device performance over time.