Enhancing Charge-Emitting Shallow Traps in Metal Halide Perovskites by >100 Times by Surface Strain

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Low deep trapping defect density is crucial for high-performance metal halide perovskites (MHPs).
• Shallow traps in MHPs are proposed to extend charge recombination lifetime but their nature and impact are unclear.
• Understanding shallow traps is key to optimizing MHP optoelectronic devices.

Purpose of the Study:

• To investigate the chemical nature, distribution, and impact of shallow traps in MHPs.
• To explore methods for controlling shallow trap density and their effect on solar cell operation.
• To elucidate the role of surface strain in shallow trap formation and MHP device performance.

Main Methods:

• Surface strain was induced by anchoring two-amine-terminated molecules onto formamidinium cations.
• Shallow trap density was correlated with surface strain and band edge shifts.
• Solar cell performance was analyzed under conditions of enhanced shallow trap density.

Main Results:

• Shallow traps are significantly more abundant in MHPs than in traditional semiconductors.
• Shallow trap density increased over 100-fold due to local surface strain, indicating surface localization.
• Surface strain caused band edge downshifting, forming shallow traps and reducing open-circuit voltage loss to 317 mV.

Conclusions:

• Shallow traps are a dominant defect type in MHPs, primarily located at surfaces.
• Surface strain is an effective method to controllably increase shallow trap density.
• High-density shallow traps can improve solar cell efficiency by mitigating recombination losses.