Researchers at the Tokyo Institute of Technology (Tokyo Tech) have made a significant breakthrough in the quest for stable and efficient solar cell materials.
Researchers at the Tokyo Institute of Technology (Tokyo Tech) have made a significant breakthrough in the quest for stable and efficient solar cell materials.
They have discovered a novel approach to stabilize α-FAPbI3, a promising solar cell material with a cubic perovskite structure, which is metastable at room temperature. By introducing a pseudo-halide ion-like thiocyanate (SCN-) into its structure, the researchers have unlocked the potential of this material for more affordable and reliable solar energy production.
α-FAPbI3, or α-Formamidinium lead iodide, has garnered attention for its excellent photophysical properties, making it a prime candidate for solar cell applications. Solar cells made from α-FAPbI3 exhibit a remarkable conversion efficiency of 25.8% and possess an energy gap of 1.48 eV, making them highly suitable for practical use. However, a major drawback has been its metastability at room temperature, leading to phase transitions when exposed to water or light.
Maintaining the α-phase is crucial for solar cell applications as it has the desired energy gap for efficient energy conversion. To tackle this challenge, the Tokyo Tech research team, led by Associate Professor Takafumi Yamamoto, devised a strategy to stabilize α-FAPbI3 by introducing thiocyanate ions (SCN-).
Previous studies had hinted at the potential for stabilizing α-FAPbI3 by partially replacing iodide ions (I-) on the surface with SCN- ions. However, the precise mechanism of how SCN- ions integrate into the perovskite lattice and enhance interfacial stability remained unclear.
In a groundbreaking development, the researchers prepared single crystal and powder samples of the thiocyanate-stabilized pseudo-cubic perovskite. Structural analysis revealed that it exhibited a √5-fold superstructure of the cubic perovskite with ordered columnar defects, forming the α’-phase. This new material exhibited an energy band gap of 1.91 eV and demonstrated thermodynamic stability at room temperature in a dry atmosphere.
One remarkable finding was the role of the α’-phase in stabilizing the α-phase, significantly reducing the transition temperature by over 100 K. The defect-ordered patterns in the α’-phase were found to create a coincidence-site lattice at the twinned boundary, contributing to the stabilization of the α-phase. This stabilization could occur either through a reduction in nucleation energy or thermodynamic stabilization via epitaxy.
This breakthrough has the potential to open new avenues of research into how defect tolerance and vacancy ordering influence the stability of halide perovskites. It represents a significant step towards harnessing the full potential of α-FAPbI3 for affordable and efficient solar energy production, bringing us closer to addressing global energy challenges and mitigating climate change.