Space charge limited conduction in ultrathin PbS quantum dot solid diodes

Abstract

As a simple and direct characterization of carrier transport in nanocrystal quantum dot (NQD) solids, current-voltage characterization of ultrathin diodes is proposed. We found the space charge limited conduction (SCLC) behavior in ultrathin PbS NQD diodes with active layer thickness half of the full depletion width; and extracted hole concentrations in the order of 10(15) cm(-3), hole mobilities from 10(-4) to 10(-5) cm(2)/Vs, trap energy depths varying from 140 meV to 200 meV, and volume trap density around 10(17) cm(-3) for thin films with NQDs of diameters 3.3 and 3.6 nm, respectively. We further discuss the validity of applying SCLC to the NQD solids based diodes and the implications of the extracted parameters extensively. Proposed characterization method here is a direct measure of carrier transport in solar cell structures which could provide exact directions in NQD solids based solar cell fabrication and modeling.