Ultrafast hole relaxation between dual valence bands in methylammonium lead iodide

Hybrid organometal halide perovskites have attracted much attention owing to their high conversion efficiencies in solar cell applications. Besides this, hybrid organometal halide perovskites have also been demonstrated to be promising for light-emitting diodes, lasers, and field-effect transistors. Harvesting excess energy of hot carriers is desirable to improve the efficiency of solar cells. The excitation of electrons in the dual valence bands of methylammonium lead iodide (MAPI) creates hot holes in the higher-energy valence band, providing the possibility to harvest large excess energy of hot holes. The optical-pump THz-probe spectroscopy unveils the relaxation of the hot holes from one valence band to the other, paving the road to harvest hot holes in MAPI-based solar cells.Methylammonium lead iodide exhibits dual valence bands. A pump at 400 nm excites the transition between VB2 and CB1, creating holes in VB2 (lighter and more conductive) that relax to VB1 rather than directly recombine with the electrons in CB1.