Exclusive Electron Transport in Core@Shell PbTe@PbS Colloidal Semiconductor Nanocrystal Assemblies

Assemblies of colloidal semiconductor nanocrystals (NCs) in the form of thin solid films leverage the size-dependent quantum confinement properties and the wet chemical methods, vital for the development of the emerging solution-processable electronics, photonics, and optoelectronics technologies. The ability to control the charge carrier transport in the colloidal NC assemblies is fundamental for altering their electronic and optical properties for the desired applications. While surface doping and ligand manipulations have been very effective, they generally suffer from the sample-to-sample variability and insufficient long-term retention of the surface stoichiometries due to environmental effects. Wherever possible and applicable, the formation of a more stable core@shell morphology wherein shell acts as a dopant and carrier-regulating region is preferred. For many applications in devices where charge carrier transport functionality is one of the most prominent, the role of shells in the core@shell NCs is still not well understood. Here we demonstrate exclusive electron transport in the assemblies of core@shell PbTe@PbS colloidal NCs. In contrast to the ambipolar characteristics demonstrated by many narrow bandgap NCs, the core@shell NCs exhibit exclusive <i>n</i>-type transport; <i>i.e.</i>, drastically suppressed contribution of holes to the overall transport. The PbS shell that forms type-II heterojunction assists the selective carrier transport by heavy doping of electrons into the PbTe-core conduction level and simultaneously strongly localizes the holes within the NC core valence level. The demonstration of exclusive electron transport in this core@shell NCs is beneficial for their applications in devices or device components where ambipolar characteristics of the materials should be strongly suppressed, such as in thermoelectric and electron transporting layers in light-emitting diodes or solar cells. The stability of the electron transport in these core@shell NCs and the tuning of the heterojunction formation by the shell thickness control and modification will be also discussed. <br/><br/>References:<br/>[1] R. Miranti, D. Shin, R. D. Septianto, M. Ibáñez, M. V Kovalenko, N. Matsushita, Y. Iwasa, S. Z. Bisri, <i>ACS Nano </i>14, 3242 (2020)<br/>[2] R. Miranti, R. D. Septianto, M. Ibáñez, M. V Kovalenko, N. Matsushita, Y. Iwasa, S. Z. Bisri, <i>Appl. Phys. Lett. </i>17, 173101 (2020)<br/>[3] R. Miranti, S. Z. Bisri et al. <i>in preparation</i>