Unveiling Ultrafast Carrier Extraction in Highly Efficient 2D/3D Bilayer Perovskite Solar Cells

The development of multidimensional heterostructure (2D/3D) lead halide perovskites has emerged as an effective approach to enhancing the efficiency and long-term stability of perovskite solar cells (PSCs). However, a fundamental understanding of the working mechanisms, such as carrier extraction, and carrier transfer dynamics in the multidimensional perovskites heterostructures remains elusive. Here, we observe the ultrafast carrier extraction in highly efficient 2D/3D bilayer PSCs (power conversion efficiency of 21.12%) via femtosecond time-resolved pump-probe transient absorption spectroscopy (TAS). Notably, the formation of quasi-equilibrium states resulting in a subband absorption feature with an ultrafast lifetime of 440 fs was observed, and this feature is found only in 2D/3D perovskite heterostructure. The short-lived feature gives rise to the local electric-field-induced electroabsorption, resulting in an enhanced power conversion efficiency in 2D/3D PSCs. These findings can help comprehend the advanced working mechanism of highly efficient solar cells and other 2D/3D bilayer perovskite-based optoelectronic devices.