Heterojunction Area-Controlled Inorganic Nanocrystal Solar Cells Fabricated Using Supra-Quantum Dots.

A supra-quantum dot (SQD) is a three-dimensional structure formed by the attachment of quantum dots. The SQDs have sizes of tens of nanometer and they maintain the characteristics of the individual quantum dots fairly well. Moreover, their sizes and elemental compositions can be tuned precisely. On the basis of their unique features, in this work, SQDs are used as constituents of the interpenetrating photoactive layers of inorganic nanocrystal p-n heterojunction solar cells to control the p-type and n-type domain sizes (i.e., p-n heterojunction areas) for optimizing the charge-carrier collection. SQD-containing p-n heterojunction solar cells exhibit improved charge transport and thereby higher power conversion efficiency (PCE) (3.03%) owing to their intermediate p-type and n-type domain sizes, which are between those of a bilayer nanorod p-n heterojunction solar cell (PCE: 1.21%) and an interpenetrating nanorod p-n heterojunction solar cell (PCE: 2.40%). This work demonstrates that the self-assembly of nanoscale materials can be utilized for tailoring the spatial distributions of charge carriers, which is beneficial for obtaining an enhanced device performance.