Hot Hole Transfer Dynamics from CsPbBr₃ Perovskite Nanocrystals

Abstract

Transfer of the hot\ncharge carriers prior to their cooling to the\nband-edge states can enhance the efficiency of a semiconductor-based\nsolar cell much beyond its Shockley–Queisser (SQ) limiting\nvalue. Herein, we explore transfer of hot holes from the APbBr₃ nanocrystals (NCs) employing a carefully chosen molecular\nsystem, 4-mercaptophenol. Ultrafast pump–probe and fluorescence\nmeasurements indeed confirm this transfer process, whose efficiency\ndepends on the energy content of the hole, and a maximum efficiency\nof ∼43% is achieved with CsPbBr₃ NCs for a photoexcitation\nenergy of ∼1.46<i>E</i>_g (<i>E</i>_g is the band gap of the NCs). While the estimated hot\nhole cooling and transfer rates are quite comparable, hole transfer\nfrom the band edge is found to be a significantly slower process.\nThe findings of the present study suggest that exceeding the SQ efficiency\nof the solar cells based on the perovskites can indeed be a reality.