Abstract
Colloidal metal oxide nanocrystals offer a unique combination of excellent low-temperature solution processability, rich and tuneable optoelectronic properties and intrinsic stability, which makes them an ideal class of materials as charge transporting layers in solution-processed light-emitting diodes and solar cells. Developing new material chemistry and custom-tailoring processing and properties of charge transporting layers based on oxide nanocrystals hold the key to boosting the efficiency and lifetime of all-solution-processed light-emitting diodes and solar cells, and thereby realizing an unprecedented generation of high-performance, low-cost, large-area and flexible optoelectronic devices. This review aims to bridge two research fields, chemistry of colloidal oxide nanocrystals and interfacial engineering of optoelectronic devices, focusing on the relationship between chemistry of colloidal oxide nanocrystals, processing and properties of charge transporting layers and device performance. Synthetic chemistry of colloidal oxide nanocrystals, ligand chemistry that may be applied to colloidal oxide nanocrystals and chemistry associated with post-deposition treatments are discussed to highlight the ability of optimizing processing and optoelectronic properties of charge transporting layers. Selected examples of solution-processed solar cells and light-emitting diodes with oxide-nanocrystal charge transporting layers are examined. The emphasis is placed on the correlation between the properties of oxide-nanocrystal charge transporting layers and device performance. Finally, three major challenges that need to be addressed in the future are outlined. We anticipate that this review will spur new material design and simulate new chemistry for colloidal oxide nanocrystals, leading to charge transporting layers and solution-processed optoelectronic devices beyond the state-of-the-art.
Highlights
These materials with intriguing optoelectronic properties can be processed as thin films by high-throughput and vacuum-free printing and coating techniques, such as inkjet-printing, roll-toroll printing and blade-coating.[8,9,10,11,12,13,14,15,16] Many printing and coating procedures can be completed at low temperatures
The results showed that the use of 2-ethyl-hecanethialate as surface ligands improved the external power efficiency (EPE) of the quantum-dot LEDs (QLEDs) by B30% due to the improved charge transport of the quantum dots (QDs) films
Colloidal oxide nanocrystals offer a unique combination of excellent low-temperature solution processability, rich and controllable optoelectronic properties and intrinsic stability, which spurred their applications as charge transporting layers (CTLs) for solution-processed solar cells and light-emitting diodes (LEDs) (Fig. 19)
Summary
These materials with intriguing optoelectronic properties can be processed as thin films by high-throughput and vacuum-free printing and coating techniques, such as inkjet-printing, roll-toroll printing and blade-coating.[8,9,10,11,12,13,14,15,16] Many printing and coating procedures can be completed at low temperatures. Xiaoyong Liang is currently a PhD candidate under the supervision of Professor Yizheng Jin in the State Key Laboratory of Silicon Materials, School of Materials Science and Engineering at Zhejiang University He has keen interest in interfacial engineering of solution-processed optoelectronics using metal oxides as charge-transport layers. Krebs and co-workers prepared polymer solar cell modules in which ZnO nanocrystals were deposited as ETLs by a modified slot-die coating procedure.[26,27] These facts highlight a promising future of integrating colloidal oxide nanocrystals as CTLs in solutionprocessed LEDs and solar cells to achieve high-performance, low-cost and large-area devices. The progress of utilizing colloidal oxide nanocrystals as CTLs for solution-processed LEDs and solar cells is based on the developments of two important research fields, synthetic chemistry of colloidal oxide nanocrystals and interfacial engineering of optoelectronic devices.
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