Influence of Interparticle Structure on the Steady-State and Transient Current within Arrays of Thiocyanate-Treated PbS Nanocubes

This paper describes the dependence of the DC conductivity, film charging dynamics, and transient photocurrent dynamics of quasi-two-dimensional arrays of thiocyanate-capped PbS nanocubes (NCs) on the edge length of the NC. Arrays were prepared monolayer-by-monolayer using self-assembly at a liquid-air interface. Across-film conductivity increases with NC size with a dependence consistent with a simple diffusional hopping model. Upon application of a constant source-drain bias, the measured dark current decays exponentially to a nonzero steady-state value as immobile hole traps fill. Illumination with 532-nm light produces a repeatable photoresponse, which also fits to an exponential function. The lifetimes associated with decay of the dark current and growth of the photocurrent both increase with increasing NC size. Comparison of the electrical data with electron microscopy images reveals that this trend is related to the connectivity of the percolation networks within the film, which depends on the interparticle order and, in turn, on the edge length of the NCs. Correlations between interparticle order and electrical properties are made possible by the highly ordered films that result from the liquid-air interface deposition method. (Graph Presented).