TIPS pentacene

In an attempt to combine band-Uke charge carrier motion realized in an -inevitably fragile - crystalline FET structure with structural robustness and flexibility, Sakanoue and Sirringhaus [167] prepared FETs using spin coated films of 6,13-bis(triisopropylsilylethynyl)(TIPS)-pentacene films in contact with a perfluorinated, low dielectric-constant polymer gate electrode. The (linear) hole mobility at room temperature is 0.8 cm /V s with tendency of an apparent band-like negative temperature coefficient of the mobility (d/i/dT < 0). 

Fig. 3.7. The structure of several functionalized pentacenes. (a) TIPS-pentacene, one of a family bulky group functionalized pentacenes developed by Anthony et al. [25]. (b) A soluble conversion material which can be printed and then converted into an insoluble transistor through heat exposure [26]. (c) A thiophene containing pentacene analog which incorporates a thiophene ring for greater stability [27]...

Fig. 5 Diffusional intermolecular singlet fission, (a) Energy diagram of singlet fission via a [T-T] intermediate. In TIPS-pentacene (13) formation of two triplet excitons is exothermic whilst for TIPS-tetracene (14) this process is endothermic, reflected in the respective triplet yields for the two molecules (b). (c) Schematic depicting the collision of TIPS-pentacene in solution to form the excimer intermediate. Adapted from ref, 28,...

Better resolution of an excimer intermediate in fission was achieved in a more recent study of TIPS-tetracene solutions (Fig. 7). In this work, the diffusion-limited dynamics, endothermic energetics and unusually sharp triplet exciton absorption features enabled identification of a spectroscopically distinct intermediate state in transient absorption and photoluminescence. In contrast to TIPS-pentacene, TIPS-tetracene represents a typical tetracene system where singlet fission is endothermic by 200 meV. This endothermicity is well known to have a drastic effect on the rate of fission in the solid state where triplet formation occurs three orders of magnitude slower in films of tetracene than in pentacene. Recent work suggests that fission in tetracene may not require thermal activation. Notably, the decay of singlet excitons and the rise of triplet exciton absorption have been shown to occur independent of temperature. A low-lying, dark intermediate state in tetracene was invoked to explain these observations, however it had been difficult to isolate such a state experimentally. ... 

Technical issues in printed electrodes were briefly reviewed for all-printed TFT applications. Surface morphology and edge waviness of the printed electrode should be well controlled to produce uniform and stable TFT behavior and consistent thin-film device performances. This investigation fabricated solution-process TIPS-pentacene based TFT with the printed silver electrodes. Solution-process materials can be readily combined with a low-cost printing process, which can significantly reduce complexity in the fabrication and manufacturing process. In addition, these types of solution-process TFT can be fabricated at low temperatures and they can be also readily implemented on plastic substrates for flexible electronics applications. 

SIMS measurements by Hamilton et al. directly indicate accumulation of TIPS-pentacene within the top 15 nm of a blend film and results by Ohe et al. [10] show accumulation at both top and bottom interfaces (Figure 8.6). Similarly for TESADT ... 

Figure8.6 SIMS data forTIPS-pentacene blends demonstrating vertical phase separation, (a) ATIPS-pentacene PTAA blend from Ref [33], and (b) a TIPS-pentacene PaMS blend from Ref [10]. Silicon ions were used as...

Figure 8.7 Neutron reflectivity measurements on deuterated TIPS-pentacene PccMS blends. PaMS had molecular weights of (a) l.SkgmoP and (b)...

Most of the discussion thus far has focused on thin films produced by spin casting. However, one goal of these composite systems, and the acene blends in particular, is to improve processability during printing, especially inkjet printing. TIPS-pentacene-based OFETs fabricated by inkjet-printed semiconductor have been... 

Attempts have been made to deposit TIPS-pentacene from solution as the functional layer in a pentacene/C60 bilayer photovoltaic device. Careful optimization of deposition conditions, optimal concentration of mobile ion dopants, thermal postfabrication annealing, and the addition of an exciton-blocking layer yielded a device with a moderate white-light PCE of 0.52% [41]. Since TIPS-pentacene derivatives rapidly undergo a Diels-Alder reaction with fiillerene, the assembly of potentially more efficient bulk-heterojunction photovoltaic devices from TIPS-pentacene and fiillerene derivatives were not possible [42]. The energy levels of the TIPS-pentacene-PCBM adduct (PCBM is [6,6]-phenyl C61-butyric acid methyl ester) ineffectively supports the photoinduced charge transfer. 

Introduction of fluorine substituents into the conjugated core is known as a powerful method to change the polarity of the main charge carriers in organic semiconductors. Some fluorine derivatives of pentacene and TIPS-pentacene have also have been reported (Fig. 9). Solely perfluorinated pentacene 5AC-F14 exhibited n-type behavior with an electron mobility up to 0.22cm s [43, 44],... 

Figure 13.5 Optical microscopy and polarized images of inkjet-printed droplets of TIPS pentacene, using chlorobenzene as the major solvent mixed with 25% of the minor solvents (a) chlorobenzene, (b) hexane, (c) o-dichlorobenzene, and (d) dodecane. (Scale bar represents 50 mm.) The profilometery images of single dots using chlorobenzene mixed with 25% minor solvents, (e) chlorobenzene, (f) hexane, (g) o-dichlorobenzene, are also shown. Reproduced from ref. 10 with the permission of Wiley-VCH Verlag GmbH Co. KGaA, 2014.

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