Charge Trapping and Detrapping in CsPbBr<sub>3</sub> Perovskite Nanocrystals: Implications for Photovoltaic and Photocatalysis Applications
Brener R. C. Vale, Diego Scolfaro, Claudevan A. Sousa, André F. V. Fonseca, Luiz G. Bonato, Ana F. Nogueira, Jefferson Bettini, Lázaro A. Padilha
Abstract
High Resolution Image Download MS PowerPoint Slide Perovskite nanocrystals (PNCs) have emerged as a promising platform for the development of highly efficient nanomaterial-based lighting devices. Although experiments and calculations have shown that defect densities are on the order of 10 11 –10 16 cm –3 in bulk perovskites, this is not true for nanomaterials because they present higher defect densities. To understand the origin and relative contribution of those defects, we employed transient absorption spectroscopy and time-resolved photoluminescence. We scrutinize the exciton dynamics in PNCs for over 7 orders of magnitude in time, and we conclude that, in the ensemble of CsPbBr 3 PNCs, excited carriers can take different paths to return to the fundamental level: electron traps (hundreds of picoseconds), surface traps (2–5 ns), direct radiative recombination (∼10 ns), and delayed emission. Our measurements revealed that the excitonic component of PNCs tends to decrease with increasing nanocrystal (NC) size. On the other hand, we observed that the electron trap decay amplitude correlates with the relative delayed emission contribution, suggesting that the recombination of detrapped species comes from electron-trapping sites. Besides, the relative contribution of delayed emission is size-dependent and increases with the NC size, achieving about 80% of reversibility. Although the excitonic contribution of larger NCs is lower compared to the smaller ones, the results suggest that electron traps are reversible and do not decrease the photoluminescence quantum yield of the NCs. These results can be useful for applications that involve charge-carrier extraction, such as photovoltaics and photocatalysis.