Trap states in lead iodide perovskites

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Perovskite solar cells show high efficiency, driving research into photo carrier generation.
• Understanding trap states is crucial for improving perovskite solar cell performance.
• Defects and trap states can significantly hinder device efficiency and stability.

Purpose of the Study:

• To provide direct evidence of hole and excitonic trap states in perovskite thin films.
• To investigate the influence of dimensionality on excitonic trap behavior.
• To elucidate the role of chloride in mitigating trap states and enhancing solar cell performance.

Main Methods:

• Experimental investigation of trap states in three-dimensional (3D) and two-dimensional (2D) perovskite thin films.
• Analysis of excitonic traps below optical gaps and their dependence on dimensionality.
• Comparison of trap densities in perovskite films with and without chloride incorporation.

Main Results:

• Direct evidence for surface hole traps and sub-gap excitonic traps in CH3NH3PbI3 perovskite films.
• Excitonic trap density increases with decreasing dimensionality from 3D to 2D perovskites.
• Chloride presence reduces excitonic trap density in CH3NH3PbI3 films by over an order of magnitude.

Conclusions:

• Trap states, likely due to electron-phonon coupling, are detrimental to perovskite solar cell performance.
• Dimensionality plays a critical role in the prevalence of excitonic traps.
• Chloride incorporation is a key factor in reducing trap states and improving the performance of perovskite solar cells.