5 research outputs found
Critical Evaluation of Organic Thin-Film Transistor Models
Thin-film transistors (TFTs) represent a wide-spread tool to determine the
charge-carrier mobility of materials. Mobilities and further transistor
parameters like contact resistances are commonly extracted from the electrical
characteristics. However, the trust in such extracted parameters is limited,
because their values depend on the extraction technique and on the underlying
transistor model. We propose a technique to establish whether a chosen model is
adequate to represent the transistor operation. This two-step technique
analyzes the electrical measurements of a series of TFTs with different channel
lengths. The first step extracts the parameters for each individual transistor
by fitting the full output and transfer characteristics to the transistor
model. The second step checks whether the channel-length dependence of the
extracted parameters is consistent with the model. We demonstrate the merit of
the technique for distinct sets of organic TFTs that differ in the
semiconductor, the contacts, and the geometry. Independent of the transistor
set, our technique consistently reveals that state-of-the-art transistor models
fail to reproduce the correct channel-length dependence. Our technique suggests
that contemporary transistor models require improvements in terms of
charge-carrier-density dependence of the mobility and/or the consideration of
uncompensated charges in the transistor channel.Comment: 20 pages, 10 figure
Critical Evaluation of Organic Thin-Film Transistor Models
The thin-film transistor (TFT) is a popular tool for determining the charge-carrier mobility in semiconductors, as the mobility (and other transistor parameters, such as the contact resistances) can be conveniently extracted from its measured current-voltage characteristics. However, the accuracy of the extracted parameters is quite limited, because their values depend on the extraction technique and on the validity of the underlying transistor model. We propose here a new approach for validating to what extent a chosen transistor model is able to predict correctly the transistor operation. In the two-step fitting approach we have developed, we analyze the measured current-voltage characteristics of a series of TFTs with different channel lengths. In the first step, the transistor parameters are extracted from each individual transistor by fitting the output and transfer characteristics to the transistor model. In the second step, we check whether the channel-length dependence of the extracted parameters is consistent with the underlying model. We present results obtained from organic TFTs fabricated in two different laboratories using two different device architectures, three different organic semiconductors and five different materials combinations for the source and drain contacts. For each set of TFTs, our approach reveals that the state-of-the-art transistor models fail to reproduce correctly the channel-length-dependence of the transistor parameters. Our approach suggests that conventional transistor models require improvements in terms of the charge-carrier-density dependence of the mobility and/or in terms of the consideration of uncompensated charges in the carrier-accumulation channel
Printed Copper Nanoparticle Metal Grids for Cost‐Effective ITO‐Free Solution Processed Solar Cells
Copper nanoparticle inks have drawn much attention since they have the potential to constitute an alternative cost-effective solution than other noble metals nanoparticle inks such as Ag for indium tin oxide (ITO)-free printed electronic applications. Our research and development efforts have produced high conductivity copper nanoparticle inks which have excellent jetting and printing properties resulting in high quality inkjet-printed (IJP) Cu nanoparticle-based metal grids. We present ITO-free, Si-PCPDTBT: PC[70]BM organic photovoltaics (OPVs) processed in ambient low-cost fabrication conditions comprising for the first time embedded and non embedded inkjet-printed copper grid/Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the bottom electrode with power conversion efficiencies (PCE) of 2.56 and 3.35%, respectively. The results of the ITO-free OPVs using inkjet-printed Cu nanoparticle current collecting grids are discussed relevant to reference ITO-based OPVs with PCE of 4.92%
Up-scalable ITO-free organic light emitting diodes based on embedded inkjet-printed copper grids
We report on ITO-free OLEDS with a transparent hybrid Cu nanoparticle grid/PEDOT:PSS electrode processed in ambient conditions. An experimentally based methodology was implemented, where studies on alternative PEDOT:PSS derivatives and Cu grid design were performed, to gradually increase the efficiency of lab scale ITO-free OLEDs. To further increase electrode performance, inkjet-printed (IJP) Cu-grids are embedded to flatten the electrode, reduce leakage current and enhance homogeneity and efficiency. Finally, embedded Cu based ITO-free OLEDs showed current and power efficiencies comparable to reference ITO-based OLEDs. Methods to manufacture large area flat embedded IJP Cu-electrodes on glass and flexible substrates are presented and upscaling prospects of the proposed ITO-free electrode are discussed