Charge Transport Dilemma of Solution-Processed Nanomaterials

Abstract

A large variety of nanoparticles were synthesized during the last 25 years and are used now as “building blocks” for a variety of materials. Bottom-up solution processing of devices emerged as a promising direction of their technological applications because this method can (a) utilize intrinsic ability of nanocolloids to self-organize, (b) reduce high energy and equipment cost of device manufacturing, and (c) impart new functionalities to electronic devices. However the technological impact of solution processable semiconductor materialsalthough potentially considerablehas been so far limited because of the long-standing dilemma between the need for effective colloidal stabilization of nanoparticles and effective charge transport. Surfactants and other organic materials being used to synthesize and/or disperse nanocolloids introduce a barrier for charge transport between the particles. Although these barriers do make it impossible to use them in electronic devices, they certainly make it more difficult. In this review, we look into the latest progress in the solution processable devices and methods to produce electrically conductive thin films from nanoscale dispersions. We are specifically interested in the understanding of the prospects of self-assembly to facilitate charge transport and nanoscale connectivity during solution processing. The updated theoretical description of charge transport in nanoparticle solids and similar nanomaterials is also given. It includes consideration of the key mechanisms such as tunneling and cotunneling, as well as key electrical parameters characterizing transport of electrons through the surfactant-related barriers, such as coupling energy and Coulombic charging energy. Manifestations of these mechanisms in different electronic materials made from nanoparticles, nanowires, nanotubes, and nanosheets and their relative advantages and disadvantages are also discussed. We conclude the topic with a brief description of new opportunities and approaches to improve charge transport in solution processed materials from nanoscale dispersions.

Quantifying Angular Correlations between the Atomic Lattice and the Superlattice of Nanocrystals Assembled with Directional Linking

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Typically, the utilized ligands consist of wide-gap, bulky hydrocarbons which render the MCs insulating. [26][27][28][29][30][31][32][33] MCs obtained in this way exhibit average grain sizes of ~150 µm 2 , which enables a detailed characterization by electron and/or X-ray microscopy. 34 Since the optoelectronic properties of PbS NC ensembles bear many opportunities for applications in solar cells or photodetectors, a number of ligand exchange procedures with small organic or inorganic molecules as well as single atom passivation strategies have been developed, all of which greatly increase the carrier mobilities within the SL of NCs.…”

Metal Domain Size Dependent Electrical Transport in Pt-CdSe Hybrid Nanoparticle Monolayers

“…This usually leads to a high resistivity of the arrays. 31 (CZTS) and Au were recently reported to improve the photoresponse and -stability compared to pure CZTS multi-layered photodetectors. 51 Increasing the current in a semiconductor nanoparticle array by deposition of metallic domains seems intuitive.…”

Theory of a field-effect transistor based on a semiconductor nanocrystal array

“…In order to do this, we consider the case when all first layer NCs (except one NC A) contain integer number of electrons ν 1 = n i1 = ν (i = A), one NC A has one additional electron n A1 = ν + 1 electrons, all second layer NCs do not contain electrons at all, namely, n i2 = ν 2 = 0. The energy of such an electron configuration "1", H 1 , can be calculated using Hamiltonian (5). We can compare the energy of this electron configuration with the energy of configuration "2", H 2 , in which the electron moves from the first layer NC A to any second layer NC.…”

“…In the recent years, there has been growing interest in investigation of the semiconductor nanocrystals (NCs) due to their size-tunable optical and electronic properties [1][2][3][4][5] . Like in bulk semiconductors, adding charged carriers is critical for NC solids, which would otherwise be electrically insulating.…”