Strong photocharging effect in CsPbBr 3 nanocrystal films
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ORIGINAL ARTICLE
Strong photocharging effect in CsPbBr3 nanocrystal films Nawal Al Abass1 Received: 24 August 2020 / Accepted: 19 September 2020 © King Abdulaziz City for Science and Technology 2020
Abstract In this study, a strong photocharging effect has been detected by a spectroscopic study of colloidal CsPbBr3 quantum dot film. Photocharging induces the formation of charged excitons, even with the application of a very low excitation laser power. Thus, it can introduce a drastic problem on the optical properties of quantum dots when the charges are involved. The charge exciton then can absorb another photon from the next laser pulse, leading to a trion state. The presence of the trion state was proven by studying its behavior against three effects, namely laser power, electric field (EF) and temperature (T) dependence. The trion area of the peak increases linearly with the increasing of the laser power, which we consider to be an indication of the influence of a strong photocharging effect, suggesting that long-lived charges can be kept trapped in quantum dots (QDs). It was also found the trion is affected by an external electric field, due to the weak Stark effect. It is more sensitive than the excitonic state to the electric field due to the presence of electron–electron repulsion forces. A red-shift behavior was observed when heating the sample above 180 K, which is a strong evidence of the presence of a trapping state. Keywords CsPbBr3 · Stark effect · Photocharging · Quantum dots · Nanocrystal films
Introduction Cesium lead halide perovskites (CsPbX3; X = Br, Cl, I) are promising materials due to their unique confined nature and high photoluminescence quantum yield, without an extra shell/capping layer (Akkerman et al. 2015; Piveteau et al. 2020; Protesescu et al. 2015; Yakunin et al. 2015), leading to applications in solar cells, light emitting diode LEDs, lasers and photodetectors (Kojima et al. 2009; Song et al. 2015; Zhang et al. 2015), which essentially rely on the excited states’ carrier separation, recombination and transport processes (Hu et al. 2015; Piveteau et al. 2020). CsPbX3 thin films show strong quantum yields, reaching 90% (Rainò et al. 2016). This means they are considered good alternative sources for tunable light; however, fluctuations in emission intensity from individual dots have been recently Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13204-020-01565-x) contains supplementary material, which is available to authorized users. * Nawal Al Abass [email protected] 1
King Abdulaziz City for Science and Technology (KACST), National Center for Nanotechnology and Semiconductor, P.O Box 6086, Riyadh 11442, Saudi Arabia
reported (Rainò et al. 2016). This limits their applications, as it can reduce photoluminescence (PL) quantum yield by increasing the rate of nonradiative carrier recombination through the fast Auger process. The underlying physical mechanisms of PL fluctuation, such as photodarkening and fluorescence in
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