The global energy crisis and climate change have driven researchers to find alternative energy sources. One promising solution is the efficient conversion of solar energy into electrical energy using solar cells. Designing solar cells requires materials with good photophysical properties, such as light absorption. α-Formamidinium lead iodide (α-FAPbI3) has emerged as a potential candidate for solar cell applications due to its impressive conversion efficiency and desirable energy gap. However, α-FAPbI3 is metastable at room temperature and undergoes a phase transition when exposed to water or light, which hinders its practical use. In a recent study published in the Journal of the American Chemical Society, researchers from Tokyo Tech have presented a new approach to stabilize α-FAPbI3 through the introduction of a pseudo-halide ion, thiocyanate (SCN–), shedding light on the stabilization mechanism of this promising material.
Previous studies have shown that replacing surface anions of α-FAPbI3 with SCN– ions stabilizes the α-phase. However, the precise mechanism of how SCN– ions incorporate themselves into the perovskite lattice and enhance interfacial stability remains unclear. To unravel this mystery, Associate Professor Takafumi Yamamoto and his team prepared single crystal and powder samples of the thiocyanate-stabilized pseudo-cubic perovskite for the first time.
Structural analysis of the thiocyanate-stabilized pseudo-cubic perovskite revealed a √5-fold superstructure of the cubic perovskite with ordered columnar defects, forming the α’-phase. This new material was thermodynamically stable in a dry atmosphere at room temperature and exhibited an energy band gap of 1.91 eV. Interestingly, the presence of the α’-phase in samples containing the δ-phase facilitated the δ-to-α phase transformation and significantly reduced the transition temperature. The researchers attributed this stabilization effect to the defect-ordered patterns in the α’-phase, which can create a coincidence-site lattice at the twinned boundary. This can lead to the stabilization of the α-phase either by reducing its nucleation energy or through thermodynamic stabilization via epitaxy.
The findings of this study provide valuable insights into the effect of vacancy ordering and defect tolerance on the stability of halide perovskites. By utilizing pseudo-halide and grain boundary engineering, α-FAPbI3 can be stabilized, offering a pathway for the development of new thermodynamically stable solar cell materials with optimal band gaps and remarkable conversion efficiency. As Dr. Yamamoto concludes, this breakthrough paves the way for further research in the field of solar cell materials and sets a new standard for the stabilization of metastable materials.
The stabilization of α-FAPbI3, a promising solar cell material, is crucial for its practical application. Through the introduction of a pseudo-halide ion, thiocyanate (SCN–), Tokyo Tech researchers have demonstrated a successful strategy to stabilize α-FAPbI3 and enhance its interfacial stability. The structural analysis of the thiocyanate-stabilized pseudo-cubic perovskite has revealed a new α’-phase, which significantly reduces the transition temperature and promotes the δ-to-α phase transformation. These findings open up new possibilities for the development of thermodynamically stable solar cell materials with optimal band gaps and conversion efficiency. As the world seeks sustainable and clean energy sources, this study represents a significant step forward in the field of solar cell materials and lays the foundation for future advancements.