The Role of Morphology in Optically Switchable Transistors Based on a Photochromic Molecule/p‐Type Polymer Semiconductor Blend

Abstract

The correlation between morphology and optoelectronic performance in organic thin-film transistors based on blends of photochromic diarylethenes (DAE) and poly(3-hexylthiophene) (P3HT) is investigated by varying molecular weight (M w = 20-100 kDa) and regioregularity of the conjugated polymer as well as the temperature of thermal annealing (rt-160 °C) in thin films. Semicrystalline architectures of P3HT/DAE blends comprise crystalline domains, ensuring efficient charge transport, and less aggregated regions, where DAEs are located as a result of their spontaneous expulsion from the crystalline domains during the self-assembly. The best compromise between field-effect mobility (µ) and switching capabilities is observed in blends containing P3HT with M w = 50 kDa, exhibiting µ as high as 1 × 10 −3 cm 2 V −1 s −1 combined with a >50% photoswitching ratio. Higher or lower M w than 50 kDa are found to be detrimental for field-effect mobility and to lead to reduced device current switchability. The microstructure of the regioregular P3HT blend is found to be sensitive to the thermal annealing temperature, with an increase in µ and a decrease in current modulation being observed as a response to the lightstimulus likely due to an increased P3HT-DAE segregation, partially hindering DAE photoisomerization. The findings demonstrate the paramount importance of fine tuning the structure and morphology of bicomponent films for leveraging the multifunctional nature of optoelectronic devices.

A Molecular‐Switch‐Embedded Organic Photodiode for Capturing Images against Strong Backlight

“…This can be attributed to the higher quantum yield of photocyclization (0.39 ± 0.01) than that of photocycloreversion (0.02 ± 0.003) as shown in Figure S3 and Table S1, Supporting Information. [41][42][43][44] Furthermore, the thin-film absorption spectra of the DAE showed the same tendency as that described in Figure S4, Supporting Information. In this case, photocyclization began at 13.7 mW cm −2 , indicated by the generally slower dynamics of diarylethenes in solid-state films than in the solution.…”

“…Estimation of Quantum Yield: Photoisomerization quantum yield is estimated following the procedure in a previous study, [41][42][43][44] where N A is the Avogadro number, ε is the absorption coefficient, A t is the absorption value after irradiation sample for time interval t, (1−10 − A t ) is the fraction of absorbed photons, and I is the photon flux. [41,42,44] The unit correction factor is used such that the above-mentioned equation is applicable for estimating a quantum yield of photoisomerization in solid state. The calculated absorption coefficients (ε) for DAE were 7.6 × 10 4 L mol −1 cm −1 for the open form and 4.8 × 10 4 L mol −1 cm −1 for the closed form.…”

“…Photoisomerization quantum yield is estimated following the procedure in a previous study, [ 41–44 ] described by Börjesson et al. The following equation was used to determine the quantum yield (ϕ UV ) of photocyclization (i.e., conversion of open‐ to closed‐ring isomer) and quantum yield of photocycloreversion (ϕ Vis ) (i.e., conversion of closed to open ring isomer) in solid state of DAE: where N A is the Avogadro number, ε is the absorption coefficient, A t is the absorption value after irradiation sample for time interval t , (1−10 − A t ) is the fraction of absorbed photons, and I is the photon flux.…”

“…Typically, diarylethene derivatives can function as wavelength-selective molecular switches with UV light (300-400 nm), inducing photocyclization (ring-closing) and visible light (400-700 nm), inducing photocycloreversion (ring-opening). [20][21][22][23][24][25][26][27][28][29] The light-intensity-dependent switching properties of DAB are utilized such that a gradually increasing intensity of ambient light (including both UV and visible wavelengths) gradually converts open isomers into closed isomers owing to the considerably higher quantum yield of photocyclization compared to that of the photocycloreversion of DAB, which is typical for diarylethenes. As shown in Figure 1b, under weak ambient illumination, DAB molecules contain mostly open isomers with a wide highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, and hence, do not affect the junction properties of Schottky OPDs.…”

Ternary‐Responsive Field‐Effect Transistors and Multilevel Memories Based on Asymmetrically Functionalized Janus Few‐Layer WSe2

“…Note that direct spin‐coating of P(VDF‐TrFE) solution onto the DAE/WSe 2 chip is avoided since the solvent (methylethylketone) would remove DAE molecules, and moreover, the formation of P(VDF‐TrFE) film requires curing at 140 °C for 2 h to increase its crystallinity, which may deteriorate the switching capacity of the DAE molecules. [ 23 ]…”