Compositionally Engineered Ternary PbS_xSe_1-x Quantum Dots Active in Short-Wavelength Infrared Region

Lead chalcogenide Quantum Dots (QDs) possess versatile attributes, primarily due to their large exciton Bohr radius and extensive infrared radiation absorption capabilities. Among them, PbS and PbSe QDs have been integrated into various optoelectronic devices, such as solar cells and photodetectors, showcasing superior performance. Notably, their excellent absorption properties in the SWIR region underscore their potential in LiDAR systems. Although PbSe QDs display superior mobility characteristics compared to PbS,[1] they have a lower chemical yield. Furthermore, lead chalcogenide QDs exhibit size-dependent air-stability,[2] with PbSe showing significantly compromised air-stability, especially in the SWIR region. PbS_xSe_1-x QDs might provide an alternative solution to overcome these critical shortcomings.

Long Hu et al. highlighted enhanced mobility in FETs and better PCE in solar cells through the simple admixture of PbSe with PbS.[3] Wanli Ma et al. described PbS_xSe_1-x QDs that exhibited improved J_sc compared to PbS and enhanced V_oc relative to PbSe.[4] Despite the potential of PbS_xSe_1-x QDs in photovoltaic applications, a deeper investigate into their air-stability and other material properties remains essential. Additionally, studies to date have not conclusively explored properties concerning compositional shifts, primarily because inevitable wavelength alterations occur with changes in the anion ratio.

We successfully synthesized PbS_xSe_1-x QDs active in the SWIR region through a simple synthesis method by injecting a mixture of anion precursors. The QDs, synthesized uniformly, were compositionally engineered to absorb within a consistent wavelength range. Compared to the chemical yield observed in PbSe QDs, there was a marked enhancement for our PbS_xSe_1-x QDs with the yield being approximately three times greater. Under ambient conditions, the blue shift phenomenon resulting from oxidation is reduced and surface analysis provided evidence that the formation of Se oxide (either SeO₂ or SeO₃^2-) was notably diminished. The mobility in FETs was improved compared to that of PbS QDs and PbS_xSe_1-x QDs ink was produced for the first time through a ligand exchange from long chain to short. Moreover, PbS_xSe_1-x in the NIR region demonstrated solar cell efficiencies exceeding 10%, the highest on record. These findings emphasize the promising future of PbS_xSe_1-x QDs in infrared optoelectronic applications.

References
1. Lin, Q.; Yun, H. J.; Liu, W.; Song, H. J.; Makarov, N. S.; Isaienko, O.; Nakotte, T.; Chen, G.; Luo, H.; Klimov, V. I.; Pietryga, J. M. Phase-Transfer Ligand Exchange of Lead Chalcogenide Quantum Dots for Direct Deposition of Thick, Highly Conductive Films. J. Am. Chem. Soc. 2017, 139, 6644.
2. Choi, H.; Ko, J. H.; Kim, Y. H.; Jeong, S. Steric-Hindrance-Driven Shape Transition in PbS Quantum Dots: Understanding Size-Dependent Stability. J. Am. Chem. Soc. 2013, 135, 5278.
3. Hu, L.; Huang, S.; Patterson, R.; Halpert, J. E. Enhanced mobility in PbS quantum dot films via PbSe quantum dot mixing for optoelectronic applications. J. Mater. Chem. C 2019, 7, 4497.
4. Ma, W.; Luther, J. M.; Zheng, H.; Wu, Y.; Alivisatos, P. Photovoltaic Devices Employing Ternary PbS_xSe_1-x Nanocrystals. Nano Lett. 2009, 9, 1699.