Local Time-Dependent Charging in a Perovskite Solar Cell

Area of Science:

• Materials Science
• Renewable Energy
• Physical Chemistry

Background:

• Efficient solar cells require optimized internal interfaces to prevent energy losses.
• Perovskite solar cells exhibit current-voltage hysteresis due to slow interfacial processes.
• Interfacial barriers, unbalanced charge extraction, and trap states limit power conversion efficiency.

Purpose of the Study:

• To investigate the slow dynamics at internal interfaces in perovskite solar cells.
• To understand the origins of hysteresis in methylammonium lead iodide (MAPI) solar cells.
• To differentiate interfacial processes that impact device performance.

Main Methods:

• Utilized frequency-modulation Kelvin probe force microscopy (FM-KPFM) on cross sections of MAPI perovskite solar cells.
• Mapped charge density distribution and its dynamics at internal interfaces under illumination.
• Analyzed charging dynamics at selective contact/MAPI interfaces over time scales of seconds.

Main Results:

• Observed the formation of space charge layers at MAPI interfaces within seconds of illumination.
• Identified distinct differences in charging dynamics between various MAPI interfaces.
• Demonstrated that FM-KPFM can resolve interfacial dynamics not separable by conventional measurements.

Conclusions:

• Multiple processes, likely including ion migration and interfacial trap states, contribute to perovskite solar cell hysteresis.
• The observed differences in interfacial charging rates are critical for understanding hysteresis.
• Advanced microscopy techniques like FM-KPFM are essential for detailed interfacial analysis in perovskite devices.