Publication date: 3rd July 2020
Colloidal quantum dots (CQDs) have emerged as prime contenders for the next-generation thin-film optoelectronics and tandem photovoltaic (PV) technologies, thanks to their solution-processability, tunable bandgaps and strong optical absorption. This rapid rise is largely owed to: robust surface ligand exchange recipes and efficient device architectures. The state-of-the-art CQD solar cells have an n-i-p device architecture that involves a solution-phase ligand exchanged CQD absorber sandwiched between a ZnO electron transport layer (ETL) and a solid-state ligand exchanged CQD hole transport layer (HTL).
In the first part of this talk, I will present our latest insights on solid-state ligand exchange and highlight the abrupt phase transition the CQDs undergo as the ligand shell gets exchanged due to ligand-ligand coupling signaling an optimized exchange.[1] These results have direct implications on the optimization of efficient n-i-p solar cells, and are an answer to the question - what embodies an optimized ligand exchange of CQD solids? - that has traditionally been addressed via ‘trial-and-error’.
In the second part, I will discuss scalable fabrication of CQD PV and methods to boost its long-term shelf-life, operational stability and UV-tolerance. >1-year shelf-life is demonstrated for blade-coated solar cells with >10% power conversion efficiency fabricated in a high-humidity ambient environment.[2] This result highlights that solution-phase ligand exchange has made CQD PV directly compatible with low-cost, roll-to-roll fabrication. Finally, the usually-employed ZnO electron transport layer is shown to hold back further improvements in stability. An efficient replacement with ultrathin oxide bilayers is suggested.[3]
This work was performed at the King Abdullah University of Science and Technology (KAUST), Saudi Arabia in the research group of Prof. Aram Amassian (now at, NCSU, Rayleigh). ARK acknowledges fruitful collaborations with various members of Prof. Edward H. Sargent's research group at University of Toronto over the years. ARK also acknowledges helpful discussions with Dr. Joseph M. Luther, Dr. Matthew C. Beard and Dr. Giles Eperon.
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