Charge transport in nanoparticular thin films of zinc oxide and aluminum-doped zinc oxide

Abstract

In this work, we report on the electrical characterization of nanoparticular thin films of zinc oxide (ZnO) and aluminum-doped ZnO (AZO). Temperature-dependent current-voltage measurements revealed that charge transport for both, ZnO and AZO, is well described by the Poole-Frenkel model and excellent agreement between the experimental data and the theoretical predictions is demonstrated. For the first time it is shown that the nature of the charge-transport is not affected by the doping of the nanoparticles and it is proposed that the Poole-Frenkel effect is an intrinsic and universally limiting mechanism for the charge transport in nanoparticular thin films with defect states within the bandgap. and also thin-lm solar cells, where it can serve as an active 10,11 or interfacial 12,13 or electrode material.14 Moreover, ZnO is a promising material in the eld of transparent 3,4,15 and exible electronics, 15,16 because large-area solution processing on exible substrates using techniques like inkjet printing appears feasible.17,18 The solutions for lm deposition are either based on the sol-gel route or on nanoparticle synthesis. The latter has the advantage that the synthesis and the lm deposition can be separated from each other. As pointed out previously, 19,20 this allows cheap and highthroughput synthesis at elevated temperatures, while the lm deposition is achieved at lower temperatures, which is a prerequisite for the use of exible (oen polymer-based) substrates.The problem of nanoparticulate ZnO thin lms deposited at low temperatures is that they hardly reach the electric performance of zinc oxide lms based on sputtering 21 or spray pyrolysis.22 Therefore, a better understanding of the electric conduction in these lms is desired.So far, most of the charge transport studies on ZnO nanoparticle lms used the transistor device structure: Meulenkamp 23 and Roest et al. 24,25 studied ZnO nanoparticles with small sizes (z5 nm) permeated in electrolyte solutions and it was demonstrated that transport occurs via tunnelling between discrete electronic states with or without additional thermal activation depending on the characteristics of the electrolyte. 25Besides, space-charge limited conduction (SCLC) was shown for ZnO by Bubel et al. 19 and by Caglar et al. 26 (sandwich device geometry). In these two cases, 19,26 the sizes of the nanostructures were larger (above 25 nm) compared to the abovementioned reports. This might partially explain the different ndings.Discrepancies between various transport investigations were also revealed for other nanoparticular materials, e.g. for nanostructured lms of silicon. Besides hopping, 27,28 SCLC, 29 the Poole-Frenkel effect, 30,31 and tunnelling 32,33 were reported for nano-Si (porous silicon or nanoparticles). These inconsistent results further emphasize the need for a detailed description of charge transport in nanoparticular lms.In this work, the charge transport of nanoparticulate ZnO and AZO thin lms was investigated. A dispersion of ligandstabilized ZnO or...

Fully Printed Infrared Photodetectors from PbS Nanocrystals with Perovskite Ligands

“…Printing the PbS nanocrystal ink described below in detail on top of the electrodes resulted in a catastrophic destruction of the silver electrodes (Figure S2). Thus, a protective layer of ZnO nanoparticles (N10-Nanograde) was printed on top of the electrode structure, including the silver fingers and the gap regions in between the fingers. As a side effect, the ZnO layer resulted in a reduced dark current due to its hole-blocking nature. , However, the ∼20 nm thick nanoparticle film did not decrease the current measured under white-light illumination, as was proven on lithographically prepared gold electrodes (Figure S3).…”

Overcoming Electrode‐Induced Losses in Organic Solar Cells by Tailoring a Quasi‐Ohmic Contact to Fullerenes via Solution‐Processed Alkali Hydroxide Layers

“…[ 11 ] Having overcome the ligand limitations, Lenz et al recently showed that the nature and the quality of the metal oxide determine the transport mechanism. [ 12 ] Defect-related energy levels or Poole-Frenkel defects wileyonlinelibrary.com not only control the transport but also may impact the interface formation. [ 12 ] Several strategies were developed to address these issues.…”

“…[ 12 ] Defect-related energy levels or Poole-Frenkel defects wileyonlinelibrary.com not only control the transport but also may impact the interface formation. [ 12 ] Several strategies were developed to address these issues. Conjugated as well as nonconjugated polyelectrolyte interface modifi ers were shown to provide a simple and quite universal n-type interface to PCBM, which in the case of poly(imines) was hypothesized to lower the work function because of the orientation of positive charges at the contact/ active layer interface.…”

Charge Trapping Augmented Switchable Sub-band-gap Photoresponse of Zinc–Tin Oxide Thin-Film Transistor

“…Figure 1 shows the TEM cross-sectional images of ZTO TFTs with and without the AZO nanoparticle layer incorporated. The nanoparticulate AZO layer is selected as the charge trapping medium because AZO nanoparticles contain substantial surface defects, 12 which can serve as charge trapping sites. By adding an AZO nanoparticle layer between AlO x and SiO 2 , the interface is apparently rumpled (Figure 1a), which indeed provides defect sites for charge trapping.…”