Colloidal nanocrystal-based solar cells have shown great potential as next generation, low cost solar cells. However, one of the biggest scientific challenges for the colloidal nanocrystal solar cells is their low efficiency, mainly due to the loss of photo-generated charge carriers during their transport across the nanocrystal film. Both poor electronic coupling and disorder in the nanocrystal array are responsible for the carrier loss because they slow down carrier transport, leading to a high recombination-induced carrier loss.
Our study sought to improve solar cell efficiency by increasing the homogeneity of the size of nanocrystals in the film. We demonstrated a novel approach to convert the assembly of semiconductor nanocrystals into superlattice films with tunable grain sizes via electrophoretic deposition (EPD). Our work not only presents an efficient, scalable, low-cost method to fabricate thick semiconductor superlattice films; it also provides a platform that enables in situ studies of the ordering process. The study's findings can be used to explore the correlation between packing order of nanocrystals and electronic properties of colloidal nanocrystal films. We also proposed a charging mechanism, using first principles calculations, that take ligand chemistry into account, which is critical for the EPD process.
This project employs the EPD capability that Lawrence Livermore National Laboratory developed for additive manufacturing to fabricate and improve the performance of nanocrystal solar cells. As national security relies on the availability of affordable, sustainable, and secure sources of energy, our work could strengthen the Laboratory’s leadership in this field. Also, by employing base materials and the EPD capability developed within the Laboratory's manufacturing initiative and adding new functionality, we are supporting the Laboratory's core competency in advanced materials and manufacturing. Our integrated experimental and theoretical components inform each other and serve as an emblem of the Laboratory's approach to research.
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