Novel Surface Passivation Strategies for Colloidal Quantum Dot Solar Cells

Solution processable colloidal quantum dot solar cells have emerged as a promising low materials cost, low embodied production energy and high-efficiency photovoltaic technology. Since 2008, small cell efficiencies have increased from 2.1% to a certified 16.6% in 2020 [1,2]. Among colloidal quantum dot solar cells, Pb chalcogenide i.e. PbS and PbSe quantum dots stood out due to their high efficiency, simple fabrication process and good stability. PbS quantum dot cells having a record efficiency of 13.8% have been demonstrated [3]. Due to the quantum confinement effect, the bandgap of the material is size dependent. This enables both optimized-bandgap single-junction cells and multi-junction tandem devices. On the other hand, a star material, metal halide perovskite quantum dots has been rising in the quantum dots family. Since the first demonstration of &gt;10% efficiency by J. Luther’s group in 2016 [4], both efficiency and stability of perovskite quantum dot solar cells have rapidly improved with a record efficiency at 16.6% reported in 2020 [5]. <br/>The rapid development of colloidal quantum dot solar cells is largely attributed to the great research efforts leading to the advancement in materials synthesis, surface passivation, and device structure design and fabrication. Our research has been focused on surface passivation to improve device performance in terms of both efficiency and stability. Examples include the development of an effective passivation route for PbSe quantum dots using lead halide perovskite nanocrystals as Br^- or I^- sources. This approach has significantly reduced surface defect density as evidenced by enhanced PL quantum yield (PLQY) [6], leading to an efficiency of 9.2%, the highest for PbSe quantum dot cells in 2019 [7]. Surface passivation strategies for PbS quantum dots have also been developed including incorporating a thin alloyed shell on their surface leading to very high PLQY (&gt;85%), as well as incorporating KI3 in the ligand exchange process enabling an efficiency of 12.1% [8]. In this talk, details of above novel passivation approaches developed by our research team for improving quantum dot solar cells, both Pb chalcogenides and perovskites will be presented.<br/> <br/>Reference:<br/>[1] Luther J. M. et al., Nano Letters 8, 3488 (2008).<br/>[2] Hao M, et al., Nature Energy 5, 79 (2020).<br/>[3] Sun B, et al., Joule 4, 1542 (2020).<br/>[4] Swarnkar A, et al., Science 354, 92 (2016).<br/>[5] Hao M, et al., Nature Energy 5, 79 (2020).<br/>[6] Zhang Z, et al., Advanced Materials 27, 1703214 (2017).<br/>[7] Hu L, et al., Solar RRL 2, 1800234 (2019).<br/>[8] Hu L, eta al., Advanced Science 8, 2003138 (2021)