Colloidal quantum dot research has led to significant advances in synthesis methods, in material and film processing techniques, and in characterization and optimization of optoelectronic properties. Studies of novel passivation strategies, including new or hybrid ligand systems, surface engineering, core/shell strategies, and self-healing surfaces, will reduce trap states, improve carrier transport, and reduce the extent of energy level pinning. Another route to improved electronic transport in quantum dot films will rely on densifying nanocrystal films through improved packing and, ideally ordering. Such films will eliminate diversity in path length and thus tortuosity in charge transport through the device. Significant studies have been performed on the electron-transporting component yet as the optoelectronic quality of the quantum dot solid improves, even greater enhancements will be required in both the electron- and hole-accepting layers to ensure optimal performance. Research will need to adjust existing systems or apply novel material solutions, while intensely studying the interfaces between the quantum dot film and electrodes to eliminate any potential losses. Finally, as single-junction quantum dot solar cells advance and improve, a renewed focus will be placed on multiple-junction integration, with the goal of creating high-efficiency devices through improved spectral utilization and minimal loss associated with photocarrier thermalization.
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