Lifetime Blinking in InP/ZnSe_xS_1-x/ZnS Quantum Dots

We report the observation of ‘lifetime blinking’ in interface alloyed environment-friendly InP/ZnSe_xS_1-x/ZnS quantum dots (QDs) with optimal composition. Auger recombination is known to be one of the major drawback factors for self-emitting quantum dot light-emitting diode (QLED) devices. When unwanted Auger recombination is sufficiently suppressed, the charged states of QDs emit comparably to the neutral states of QDs. Rather than common blinking properties of QDs where the charging and discharging results in fluctuation in photoluminescence (PL) intensity, only lifetime variations were observed under substantial suppression of Auger recombination. The lifetime fluctuation despite nonblinking emission is referred to as ‘lifetime blinking’ and is only observed in high-quality QDs with high trion quantum yields and low non-radiative auger rates. To the best of our knowledge, this study is the first to observe lifetime blinking in non-Cd-based QDs.<br/><br/>We scrutinize the effect of various ZnSeS midshell compositions on QD performance and uncover the relationship between shell structure/composition and QD performance. Negative trion Auger recombination dynamics are studied through ensemble photoelectron doping experiments and single-dot analysis. Interface alloying successfully reduces lattice difference and smoothens confinement potential, and therefore, substantially suppresses unwanted Auger recombination. Non-radiative Auger rates drastically decrease from 0.41 ns^-1 to 0.022 ns^-1 with the introduction of a smooth shell interface. As the Auger process is suppressed, ‘lifetime blinking’ is observed since the trion quantum yield of gradient shell QD is enhanced to 81% by a factor of 4.5 compared to that of the discrete QD. Properties regarding PL peak width, including spectral diffusion and single-dot PL peak width, are also improved with the introduction of gradient shells due to reduced lattice mismatch between shells and increased charge trapping energy barrier. Yet, these performance improvements are found to be composition-dependent, requiring ZnSe rich midshell to prevent lattice strain in the interface of the core and the shell from arising. We anticipate the presented result to act as a stepping-stone towards developing environmentally friendly QLEDs with high performance.<br/><br/>[1] Lee. Y. et al. Effectual Interface and Defect Engineering for Auger Recombination Suppression in Bright InP/ZnSeS/ZnS Quantum Dots. <i>ACS Appl. Mater. Interfaces</i> <b>14</b>, 10, 12479–12487 (2022)<br/>[2] Lee. S. et al. The effects of discrete and gradient mid-shell structures on the photoluminescence of single InP quantum dots. <i>Nanoscale</i>. <b>11</b>, 23251–23258 (2019)<br/>[3] Park, Y. et al. Effect of Interfacial Alloying versus “Volume Scaling” on Auger Recombination in Compositionally Graded Semiconductor Quantum Dots. <i>Nano Lett</i>. <b>17</b>, 9, 5607–5613 (2017)<br/>[4] Kim, T. et al. Negative Trion Auger Recombination in Highly Luminescent InP/ZnSe/ZnS Quantum Dots. <i>Nano Lett</i>. <b>21</b>, 5, 2111–2116 (2021)<br/>[5] Cragg. G & Efros. A. Suppression of Auger Processes in Confined Structures. <i>Nano Lett</i>. <b>10</b>, 1, 313–317 (2010)