Organic semiconductors field effect mobility

The performance of organic semiconductor field-effect transistor has been improved tremendously in the last few years, focusing on increasing the environmental stability and charge carrier mobility of p- and n-type polymers and small molecules. In particular, for polymers the record mobility values reported till date are approaching 2cm (V s ) for p-type polymers [7] and Icm (V s ) for n-type polymers [8]. The p-type conduction has been till last few years much superior than n-type one, due to the oxygen and water sensitivity of many organic anions [9]. Only recentiy, n-type polymers with comparable performance have been reported. 

Figure 12.3. Benchmark of peer-reviewed academic reports of organic semiconductor device field-effect mobility versus time of report. All data points are for spin-coated organic semiconducting transistors. Solid points are derived from the benchmark study completed in 2002 by Brazis and Dyrc at Motorola (unpublished). The curve is a calculated estimation, based on these data, of what the expected mobility values will be in the future. The open points are data derived in 2005 from the public journals for verification of the 2002 prediction.6 38... 

There is a very short list of organic semiconductors with reported thin-film field-effect mobilities greater than 1 cm2 V-1 s h These include pentacene, sexithio-phene [5a], and anthradithiophene [17]. If we extend this list to include single crystal and n-type materials, we can add perylene [18], rubrene [19], copper phtha-locyanine (CuPc) [20], tetracyanoquinodimethane (TCNQ) [21], and dithiophene-tetrathiofulvalene (DT-TTF) [22] - still a short list. 

An alternative route to solution-processible organic semiconductors is to use precursors to small molecule semiconductors, such as pentacene [59] or tetrabenzo-porphyrin [60], which can be converted into their fully conjugated, insoluble form by thermal or irradiative [61] treatment on the substrate. Pentacene precursors have been shown to yield field-effect mobilities of 0.01-0.1 cm2 V-1 s 1 [62], and 0.1-0.8 cm2 V-1 s 1 [63] after thermal conversion at 150-200 °C. Small molecule organic semiconductors can also be rendered solution processible by attachment of flexible side chains [64-66], Due to the relatively low solubility of these molecules the growth of uniform thin films of these molecules remains challenging, however. 

Using naphthalenetetracarboxylic dianhydride as the semiconductor, changes in bulk conductivity, field-effect mobility, and threshold voltage were separately observed in response to exposure to water and oxygen [35, 36], Another more elaborate kind of pattern was produced by a virtual array of eleven different semiconductor OFET monitoring on-current in response to polar and nonpolar organic vapors [37]. Responses (0.8-0.3-fold reductions and 1.5-2-fold increases) were dis-... 

FET mobility measurements thus constitute a sound method for investigating changes in the mobility of an organic semiconductor due to morphology variations. On the basis of the FET characteristics of MDMO-PPV films spin-cast from different solvents, we will discuss the influence of interchain polymer aggregates on the hole field-effect mobility and further consequences for the short-circuiting of solar cells. 

Veres et al. have shown that the field-effect mobilities of amorphous PTAA [18] and other polymers are higher in contact with low-k dielectrics with 8 < 3 than dielectrics with higher k [19]. The latter usually contain polar functional groups randomly oriented near the active interface, which is believed to increase the energetic disorder at the interface beyond what naturally occurs due to the structural disorder in the organic semiconductor film resulting in a lowering of the field-effect... 

Field-Effect Mobility and On/Off Ratio Found in the Literature for Each Organic Semiconductor Described in the Text... 

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