Nonmonotonic Size-Dependent Carrier Mobility in PbSe Nanocrystal Arrays.
On the basis of a tight binding system-bath model, we investigated carrier mobility of PbSe nanocrystal (NC) arrays as a function of NC size and inter-NC separation. The size-dependent trend of calculated carrier mobilities are in excellent agreement with recent experimental measurements: electron mobility increased up to NC diameter of ∼6 nm and then decreased for larger NCs, whereas hole mobility showed a monotonic size-dependency. Carrier mobility increase was associated with reduced activation energy that governs charge-transfer processes. In contrast, the decrease in electron mobility for large NCs was found to be due to smaller electronic coupling. Control of inter-NC separation is crucial for mobility enhancement: the mobility may change by an order of magnitude when inter-NC separation varies by as little as 1 to 2 Å. We anticipate similar size-dependency of the mobility in other semiconductor NC arrays, although crossover diameter in which mobility reaches its maximum depends on the material.
Department of Chemistry and Institute of Nano-Bio Molecular Assemblies, Yonsei University, 50 Yonsei-ro Seodaemun-gu, Seoul 120-749, Korea.
Jihye
J
Lee
Department of Chemistry and Institute of Nano-Bio Molecular Assemblies, Yonsei University, 50 Yonsei-ro Seodaemun-gu, Seoul 120-749, Korea.
One
O
Choi
Department of Chemistry and Institute of Nano-Bio Molecular Assemblies, Yonsei University, 50 Yonsei-ro Seodaemun-gu, Seoul 120-749, Korea.
Eunji
E
Sim
PbSe; carrier mobility; charge transfer; charging energy; electronic coupling; internanocrystal separation; path integral; semiconductor nanocrystal array