Charge transport in semiconductors assembled from nanocrystal quantum dots

Abstract

The potential of semiconductors assembled from nanocrystals has been demonstrated for a broad array of electronic and optoelectronic devices, including transistors, light emitting diodes, solar cells, photodetectors, thermoelectrics, and phase change memory cells. Despite the commercial success of nanocrystal quantum dots as optical absorbers and emitters, applications involving charge transport through nanocrystal semiconductors have eluded exploitation due to the inability to predictively control their electronic properties. Here, we perform large-scale, ab initio simulations to understand carrier transport, generation, and trapping in strongly confined nanocrystal quantum dot-based semiconductors from first principles. We use these findings to build a predictive model for charge transport in these materials, which we validate experimentally. Our insights provide a path for systematic engineering of these semiconductors, which in fact offer previously unexplored opportunities for tunability not achievable in other semiconductor systems.

Simulating nanocrystal-based solar cells: A lead sulfide case study

“…Due to energetic disorder in the NC thin film, stemming from variation in the individual NC sizes and the presence of trap states, the mobility is not a well-defined quantity; however, we can extract an effective mobility experimentally via time of flight measurements 19 or, more recently, multiscale simulations 9 . We separately calculate the effective mobilities for electron and holes, !…”

Structure–Transport Correlation Reveals Anisotropic Charge Transport in Coupled PbS Nanocrystal Superlattices

“…[ 6 ] Further, we note that the orientational order of the NCs observed here might be an additional source for anisotropic charge transport as different coupling strengths have been predicted along particular AL directions. [ 5,6 ] In the present case, the most efficient transport occurs if the [110] AL direction of all NCs is iso‐oriented with the electric field.…”

“…[ 1–3 ] Computational studies have predicted that properties such as electronic coupling or charge transport are determined not only by the individual NCs but also by the degree of their organization and structure. [ 4–7 ] However, experimental proof for a correlation between structure and charge transport in NC SLs is still pending. Previous experimental research on NC SLs has either focused solely on the process of self‐organization and structural order [ 8–13 ] or, in separate studies, on charge transport, and electronic properties.…”

“…Based on these transport properties and previous reports on the importance of mid‐gap states in PbS NC materials, we believe that transport in the present material occurs predominantly via hopping through trap states close to the valence eigenstate (the 1S h state). [ 5,26,27 ]…”

Exploiting the Lability of Metal Halide Perovskites for Doping Semiconductor Nanocomposites

“… 40 Although tuning NCs composition has been attempted, 26 , 41 the introduction of a controlled amount of impurities in small structures is problematic for the preparation of heavily doped semiconductors. 42 − 44 Alternative approaches to dope NC-based solids have focused on changing the NC surface chemistry, 30 , 36 , 38 , 45 − 48 inducing partial cation exchange, 49 , 50 and blending with other NCs. 35 , 51 , 52 …”