Spin-coated Films Research Articles

Structural and optical characterization of beta-gallium oxide

Demands for cheaper solar cells have led researchers to less complex, low-temperature, vacuum-free thin-film deposition processes, like spray pyrolysis and sol–gel spin coating. Previous studies of β-Ga2O3 thin-film deposition have used aqueous solutions of gallium nitrate which have strong tendencies to form hydroxide precipitates. This leads to the blockage of spray gun nozzles. To avoid precipitation, tetrahydroxogallate (III) ammonium was used as a novelty precursor in this study for the synthesis of β-Ga2O3. In the spray pyrolysis technique, the precursor was deposited on sapphire substrates at 200 ℃, with a carrier gas pressure of 200 kPa. The same precursor, with added monoethanolamine to enhance viscosity, was used in the spin coating method. A polycrystalline β-Ga2O3 structure was obtained by post-annealing films at 750 ℃ in ambient air. The spin-coated films with thicknesses ranging from 165 to 354 nm exhibited an average crystallite size of 17.78 nm and an optical band gap range between 4.80 eV and 4.95 eV. Films produced by spray pyrolysis had thicknesses ranging between 158 and 255 nm, an average crystallite size of 17.55 nm, and a band gap ranging between 4.69 eV and 4.93 eV. From Raman spectroscopy, the molecular vibrational modes Ag and Bg were detected, featuring three blue shifts and two red shifts. Films showed a UV-blue region originating from oxygen and gallium vacancies in the lattice, an important characteristic for good photodetectors and vital for solar cell passivation. When utilizing β-Ga2O3 as dielectric coating, the refractive index between air and solar cells is reduced, enhancing solar energy absorption. Similar results were obtained for both synthesis techniques confirming the reliability of the methods.

Perovskite BaSnO3 nanoparticles for solar-driven bi-functional photocatalytic activity: PEC water splitting and Wastewater treatment

The highly crystalline n-type BaSnO3 nanoparticles with size ∼30 nm, a larger surface area of ∼15.11 m2·g−1, and a wide optical band gap of 3.24 eV have been synthesized using a co-precipitation route for applications in photoelectrochemical water splitting and organic dye degradation. The spin-coated films of BSO nanoparticles photoanodes exhibited a photocurrent density of 20 μA·cm−2 at a forward bias potential of 0.6 V, a donor carrier density of 2.56 × 1018 cm−3 with a flat band potential of −0.82 V, and four-fold increment in the photocurrent density at a small bias voltage of 0.3 V, under AM 1.5 illumination (100 mW·cm−2). Pseudo-first-order kinetic study showed 96.49 and 95.38 % degradation performance of the Methylene Blue and Crystal Violet dyes at rate constant of 0.0128 and 0.0127 min−1, respectively, under constant irradiation for 240 min in the presence of BSO NPs, which is the highest degradation efficiency reported so far for BSO photocatalyst. The scavenger study revealed the significant role of h+ and ·OH− radicals in the degradation process. Liquid chromatography-mass spectroscopy provides intermediates obtained during the photocatalytic degradation of dyes. The present study focuses on the bifunctional photocatalytic performance of the BSO NPs as a potential candidate for PEC water splitting and wastewater treatment.

Structural and spectroscopic features of naphthol green B integrated for improved light harvesting capability of organic/inorganic hybrid solar cells

Regarding the intensified interest in photovoltaic devices for a wide range of applications, here, we exploited a promising naphthol green organic dye for designing efficient organic/inorganic heterojunction for solar cell applications. The crystal and molecular structures of the spin-coated NGB thin films were inspected using XRD and FTIR techniques, respectively. A nanostructured polycrystalline film was obtained with a crystallite size of ∼76.2 nm with a stable molecular configuration. The optical properties of the films were analyzed using spectrophotometrically measured transmission and reflection. The prepared films showed high absorption over the UV–Vis–NIR regimes with a relatively small energy gap of ∼1.42 eV and a low refractive index of ∼1.48 which increased its suitability for photosensing applicability. The photovoltaic performance of the fabricated Ag/NGB/p-Si/Al heterojunction was evaluated in detail yielding promising photovoltaic characteristics with Voc ∼0.77 V, Jsc ∼18.64 mA/cm2, and PCE ∼6.49 %.

Polyfluorinated Naphthalene-bis-hydrazimide for Solution-Grown n-Type Semiconducting Films.

Naphthalene tetracarboxylic diimides (NDIs), possessing low-lying and tunable LUMO levels, are of wide interest for their aptitude to provide cost-effective, flexible, and environmentally stable n-type organic semiconductors through simple solution processing. NDI-based aromatic hydrazidimides are herein studied in relation to their chemical and environmental stability and as spin-coated stable thin films. In the case of the pentafluorinated residue, these were found to be crystalline, highly oriented, and molecularly flat (roughness = 0.3 nm), based on optical and atomic force microscopy, X-ray diffraction in specular and grazing incidence geometry, and X-ray reflectivity measurements. A new polymorph, previously undetected during the isolation of bulk powders or in their controlled thermal treatments, is found in the thin film and was metrically and structurally characterized from 2D GIWAXS patterns (monoclinic, P2/c, a = 17.50; b = 4.56; c = 14.24 Å; β = 84.8°). This new thin-film phase, TF-F5, is formed no matter whether silicon, glass, or polymethylmethacrylate substrates are used, thus opening the way to the preparation of solution-grown flexible semiconducting films. The TF-F5 films exhibit a systematic and rigorous molecular alignment with both orientation and packing favorable to electron mobility (μ = 0.02 cm2 V-1 s-1). Structural and morphological differences are deemed responsible for the absence of measurable conductivity in thin films of polyfluorinated analogues bearing -CF3 residues on the hydrazidimide aromatic rings.

Thermal Annealing Impact on Optical Properties of Spin-coated P3HT: CdS Thin Film

Polymers are flexible materials that can be easily processed and are formed into a thin film by several methods such as spin-coating, dip-coating, film-casting, and printing. The spin coating method has been extensively utilized in fabricating solution-prepared organic/inorganic electronic devices, this technique is positively efficient in generating thin film apart from being a flexible method to execute. In this study, poly(3-hexylthiophene) (P3HT) material is selected as polymer and cadmium sulphide (CdS) as nanoparticles to produce a hybrid nanocomposite thin film through the process spin-coating method. The P3HT and cadmium ion solution were used to fabricate a thin film onto a quartz glass substrate at a spin speed of 500 rpm for 10 seconds. This spin-coated thin film was heated at different temperatures such as 40°C, 80°C, 120°C, and 160°C for optical properties using a UV-Vis spectrophotometer. The UV-Vis absorption spectra of P3HT: CdS indicated absorption peaks in the UV region, which were ascribed to the band gap of the P3HT: CdS thin film. Our results showed that the optical properties of the P3HT: CdS be contingent on the annealing temperature. The film at room temperature yielded a band gap value of 1.98 eV, at 40°C it resulted in 1.99 eV. The band gap value was increased when annealed at 80°C with 2.02 eV. Annealing temperatures were then raised to 120°C and 160°C, leading to band gap values of 3.11 eV and 2.80 eV respectively.

Optimized structural, optical, and electrical properties of spin-coated Pt(II) octaethylporphyrin thin films for optoelectronic applications

Octaethylporphyrin (PtOEP) is an organic molecule that has unique optical properties, such as high fluorescence quantum yields, strong light absorption, etc. Here we investigate the structural, optical, and electrical characteristics of spin-coated PtOEP thin film. X-ray diffraction (XRD) patterns indicated an increase in the crystallite of the annealed film. Field emission-scanning electron microscope (FESEM) images clearly showed agglomeration and an increase in the nanoparticle size of the annealed film. The Raman spectra of the thin films revealed symmetrical peak positions and improved peak strength for the annealed film. UV-Vis-NIR and photoluminescence (PL) spectroscopy were used to examine optical characteristics. The findings demonstrated that energy gap and PL peak emission were significantly influenced by the grown crystallite size as well as a decrease in lattice defect concentration at the grain boundary during annealing. The optical constant and interband transition strength spectra (Jcv) were estimated and addressed. Based on the linear refractive index and optical gap, third-order nonlinear susceptibility χ(3), nonlinear refractive index n2, and two-photon absorption coefficient, βc of spin-coated PtOEP thin films were calculated and discussed. Finally, the dark current-voltage (J-V) curves were utilized to assess the diode parameters, specifically the zero-bias barrier height (ΦB) and the ideality factor (n), for the ITO/PtOEP/Al diode using thermionic emission theory. Additionally, an investigation was conducted to examine the conduction mechanism of the ITO/PtOEP/Al diode under both forward and reverse bias voltage conditions. On the basis of these findings, spin-coated PtOEP thin films were concluded to be helpful in producing cutting-edge optoelectronic devices.

Random lasing in dye-doped electrospun PMMA fibers with different emission modes

Random lasers (RLs) have significant applications in micro-nano light emitters, micro-detection, and speckle-free imaging due to their novel properties in low spatial coherence, small size and multi-emission directions. A flexible, affordable approach for creating new scattering materials has recently been suggested for electrospun fibers, which are practical materials for RLs. In this article, we employ the electrospun PMMA fibers as scatters and the DCJTB as gain materials to generate an RL system. The sample shows obvious incoherent random lasing properties. A decrease of the lasing threshold by 32 % is realized when we increase the electrospun voltage from 12 kV to 15 kV due to the generation of a small mean diameter size and concentrated diameter distribution. The lasing threshold of the DCJTB/Au NPs-doped PMMA sample is further reduced to 19.8 μJ/mm2 by incorporating Au NPs into the electrospun dye-doped fibers. This leads to a lasing threshold reduction of 40 % from the electrospun sample without doping Au NPs and 52 % from the spin-coated film sample, respectively. It indicates that the electrospun method is an efficient and practical approach to make RLs. Furthermore, using single pulse laser stimulation, we investigated several different lasing modes, including spontaneous emission, short wavelength domain, mode competition, and single mode. The actions of photon scattering are analyzed to explain the dramatic lasing process. Due to the photon scattering optical path, there are mode competition and single mode emission regions under different pump energy. The light spot quality of RL shows low spatial coherence with the useful application of speckle-free imaging. This research provides a new method of electrospun to produce low-threshold and high-quality RLs and potentially opens the door for expanding their use in optics and optoelectronic equipment.

Interface modification of MoS2/ZnO heterojunction for controllable electron flow and fabrication of high-performance UV photodetectors with fast response/recovery speed

Hetero-structured thin films, MoS2/ZnO thin films, were fabricated by adding MoS2 films under the ZnO thin films via sol-gel spin-coating method; ZnO nanoparticles were observed on the surface of sol-gel spin-coated ZnO thin films. Although ZnO nanoparticles were observed on the surface of hetero-structured thin films, the surface area of the hetero-structured thin films was higher than ZnO thin films owing to the high surface roughness of the MoS2 films. Three diffraction peaks were observed in the hetero-structured thin films at 31.74°, 34.38°, and 36.22°, which indicates heterostructure was polycrystalline, and the heterostructure was formed successfully. When the UV photodetector was fabricated by using hetero-structured thin films, the enhanced values of photocurrent, photoresponsivity and photosensitivity were observed. In addition, the hetero-structured thin films exhibited a faster response/recovery speed because the move of electrons and holes during UV illumination. Thus, it was concluded that the interface modification of the MoS2/ZnO heterojunction is an effective solution for overcoming the drawbacks of ZnO-based UV photodetectors. This approach can be considered a novel method for high-performance optoelectronics with fast response speed applicable to various fields.

H2S-sensing properties of flame-synthesized RuO2-decorated WO3 nanoparticulate spin-coated films

This work aimed to develop effective and reliable H2S gas sensors based on flame-synthesized RuO2-decorated WO3 spin-coated films. Inclusive material characterizations unveiled the decoration of 1–3 nm RuO2 nanoparticles on 10–25 nm WO3 nanoparticles with 0–1 wt% Ru. Sensing layers coated with 1–6 cycles were tested towards 0.25–10 ppm H2S at 200–400 °C under various humidity conditions (0–80 %RH). The sensors with four spin-coated layers and 0.2 wt% Ru presented a reproducibly optimum response of ∼71.0 with a fair response time of ∼ 15.1 s to 10 ppm H2S in dry ambient at 350 °C. Additionally, the optimal sensor exhibited high H2S selectivity with respect to CH3SH, CH3SCH3, C3H6O, C2H5OH, CH3OH, CH2O, C6H6, C8H10, NO2, NO, H2, CH4, CO2, C2H2, HCOOH, CH3COOH, and CH3CHOHCOOH. Furthermore, the sensors displayed decent repeatability and satisfactory medium-term stability of resistance and response. Therefore, flame-synthesized RuO2-loaded WO3 nanoparticles were promising for effective and practical H2S sensing.

Hierarchical Surface Instability in Polymer Films.

This study demonstrates hierarchical instabilities in thin films. The hierarchical instabilities display three morphological characteristics: (1) windmill-like patterns at the macroscale, (2) Bénard cells and striations at the microscale, and (3) holes at the mesoscale. Such hierarchical instabilities occurred when spin coating was performed on high-volatile solutions under a high relative humidity (RH) but were suppressed when spin coating was performed on low-volatile solutions regardless of the RH. The high-volatile solutions comprise poly(4-vinylpyridine) (P4VP) in methanol or ethanol. The low-volatility solutions comprise P4VP in propanol or butanol. P4VP molecular weights, P4VP concentrations, spin rates, and film thicknesses are not vital factors in forming hierarchical instability in spin-coated P4VP films. Instead, the formation of hierarchical instabilities depends on the RH and solvent types. Namely, the hierarchical instabilities are driven by Bénard-Marangoni convection, water vapor condensation, and disturbance of spin-up and spin-off stages during spin coating of highly volatile solutions under high RH. Mechanisms of hierarchical instabilities are interpreted in detail.

The photodetection characteristics of a Brilliant Blue-FCF implemented device for organic-based optoelectronic applications

The optical properties of sol-gel-based brilliant blue-FCF (BB-FCF) thin film are analyzed for photodetection applications. The effect of the presence of the BB-FCF interface on the microelectronic characteristics of the designated Cu/BB-FCF/n-Si device is elucidated by comparing to its reference Cu/n-Si device. The systematic investigation of photodetection properties of the integrated device is performed between the 20–100 mW/cm2 illumination intensities. First, the optical features of spin-coated BB-FCF thin film are investigated by UV–Vis measurements, and the absorbance of the film is elucidated by the efficient optical absorption in the wavelength of ∼350–700 nm with the calculated optical indirect band gap of 1.72 eV. Next, the frequency-dependent capacitive behavior, charge transport mechanism, and the electronic parameters of both the rectifying Cu/n-Si and the implemented Cu/BB-FCF/n-Si devices like the ideality factor, the barrier height, and series resistance are estimated using the Thermionic emission and Norde's function methods. Subsequently, the photodetection properties of the engineered device with a BB-FCF functional dye interface are studied under a solar simulator with different power intensities. The effect of the illumination intensity and applied reverse bias voltage on the figures of merit, including photoresponsivity, photodetectivity, response speed, and linear dynamic property, are analyzed under an illumination of 20–100 mW/cm2. The designated device with a BB-FCF interface has achieved significant and fast, stable on/off switching sensitivities, with 524 ms and 629 ms rising and falling times, respectively. Therefore, the prepared BB-FCF-based device has good and stable photoresponse performance, and the Cu/BB-FCF/n-Si architecture device may be a strong candidate for photonic and optoelectronic device applications, particularly in rapidly developing organic material-based device technology.

Detection of Per- and Polyfluoroalkyl Substances (PFAS) by Interrupted Energy Transfer.

The ubiquitous presence of per- and polyfluoroalkyl substances (PFAS) in aqueous environments has aroused societal concern. Nonetheless, effective sensing technologies for continuous monitoring of PFAS within water distribution infrastructures currently do not exist. Herein, we describe a ratiometric sensing approach to selectively detect aqueous perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at concentrations of μg ⋅ L-1 . Our method relies on the excitonic transport in a highly fluorinated poly(p-phenylene ethynylene) to amplify a ratiometric emission signal modulated by an embedded fluorinated squaraine dye. The electronic coupling between the polymer and dye occurs through overlap of π-orbitals and is designed such that energy transfer is dominated by an electron-exchange (Dexter) mechanism. Exposure to aqueous solutions of PFAS perturbs the orbital interactions between the squaraine dye and the polymer backbone, thereby diminishing the efficiency of the energy transfer and producing a "polymer-ON/dye-OFF" response. These polymer/dye combinations were evaluated in spin-coated films and polymer nanoparticles and were able to selectively detect PFAS at concentrations of ca. 150 ppb and ca. 50 ppb, respectively. Both polymer films and nanoparticles are not affected by the type of water, and similar responses to PFAS were found in milliQ and well water.

Controlled Growth of Highly Oriented Perovskite Crystals in Polymer Solutions via Selective Solvent Vapor Diffusion.

Organic-inorganic hybrid perovskites have garnered significant attention in optoelectronics owing to their outstanding tunable optical characteristics. Controlled growth of perovskite nanocrystals from solutions is key for controlling the emission intensity and photoluminescence lifetime of perovskites. In particular, most studies have focused on controlling the crystallization of perovskite through chemical treatment using chelating ligands or physical treatment via antisolvent diffusion, and there exists a trade-off between the photoluminescence intensity and lifetime of perovskites. Herein, a selective solvent vapor-assisted crystallization with the aid of a functional polymer, which nanoscale perovskite crystals are grown andante from precursor solution, is presented for tuning the crystallization and optical properties of a common halide perovskite, methylammonium lead bromide (MAPbBr3 ). The proposed method here produces perovskite nanocrystals in the range of 200-300nm. The spin-coated thin film formed from the perovskite solution exhibits strong green photoluminescence with a long lifetime. The effects of the functional group and polymer dosage on the crystallization of MAPbBr3 are systematically investigated, and the crystallization mechanism is explained based on a modified LaMer model. This study provides an advanced solution process for precisely controlling perovskite crystallization to enhance their optical properties for next-generation optoelectronic devices.

How do carbon dots with amine terminals help perovskite solar cells perform better?

Lead halide perovskite solar cells can be significantly improved with multifunctional additives such as carbon dots (CDs) with amine terminals via defect passivation and band alignment. Here, we determine rational guidelines for the usage of such quantum dots in perovskite solar cells by systematically studying their effects on crystal quality and carrier transport. The amine-terminated CDs homogeneously dispersed in precursors improve the crystal quality of perovskite films, but they reduce the hole mobility hampering hole extraction. In contrast, CDs deposited between the electron transport layer and active layer could promote spin-coated film quality and electron’s extraction efficiently. So, the approaches of the carbon dots in device alters semiconductor properties and energy level structure. Interface engineering achieve better crystal quality and energy level alignment, which in turn affects charge collection, thereby increasing current density and power conversion efficiency. According to the findings of this study, when considering defect passivation by additives, the energy band alignment of the device should also be considered, since this could change carrier dynamics and device performance differently.

Dual-functionalized poly(ethylene oxide) for interface modification and addition of rubidium-doped CsPbBr3 perovskite composite emission layer to enhance brightness of perovskite light-emitting diodes

Metal halide perovskite as an emitter has extremely high color purity, but the generally poor morphology of the perovskite layer restricts the performance of the emitter. The additive of a suitable polymer can greatly boost the uniformity of the spin-coated perovskite film. The all-inorganic perovskite layer deposited by the solution method has a multi-crystalline structure. Besides, there are a lot of defects and grain boundaries on the surface, and the carriers will undergo non-radiative recombination at these defects. In this study, Cs1-xRbxPbBr3 was prepared by introducing Rb+ cations with smaller ionic radius to partially replace Cs+ cations, and combined with poly(ethylene oxide) (PEO) and (1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole) (TPBi) blended composite film as the light-emitting layer, that can increase the film coverage and radiative recombination efficiency of the perovskite film. The polymer PEO was introduced as a buffer layer deposited on the poly-TPD hole transport layer (HTL) to to enhance the hydrophilicity and passivate the poly-TPD HTL/perovskites interface in order to obtain high-efficiency perovskite light-emitting diodes. By adjusting the concentration of the PEO buffer layer, the champion luminance and external quantum efficiency are 25650 cd/m2 and 0.844 %, respectively.

Air/Liquid Interfacial Self-Assembled Intrinsically Stretchable IDT-BT Film Combining a Deliberate Transfer Adherence Strategy for Stretchable Electronics.

Indacenodithiophene-benzothiadiazole (IDT-BT) has emerged as one of the most promising candidates for stretchable electronics due to its good stretchability and high mobility. Here, we present an air/liquid interface self-assembly method for the stretchable IDT-BT films and design an air-side transfer adherence strategy for improving the carrier mobility of IDT-BT. By controlling the cosolvent ratio in solution and the solvent evaporation rate, the large-scale intrinsically stretchable IDT-BT film with the diameter as high as ∼3 cm was self-assembled at the air/liquid interface. The resulting stretchable film with lightweight and good uniformity could be easily transferred to curved objects such as flexible 3 M tape, glass ball, and seashell. It is found that the transfer adherence strategy of the semiconductor film significantly affects the carrier transport. The transfer adherence from air-side can effectively decrease the number of the adsorbed water molecules at semiconductor/dielectric interface, which presents the mobility as high as 2.98 cm2 V-1 s-1. Based on the air/liquid interface self-assembled IDT-BT film, the peeling process of the film for preparation of full stretchable transistors could be eliminated. The resulting intrinsically stretchable transistor exhibits mobility higher than that of the transistor with a conventional spin-coated film. Our research provides new pathways for preparing the stretchable films and intrinsically stretchable organic field-effect transistors and shows the promising potential of the air/liquid interface self-assembly strategy for stretchable electronics.

Cation-cation co-doped ZnO thin films for transparent conductive oxide applications

This paper presents a recent study on the structural and transparent conductive properties of sol–gel spin-coated ZnO films, focusing on the effects of cation-cation co-doping. The co-doping combinations investigated include (Sn-Ga), (Ga-Co), and (Ga-Mg). All the films exhibit a ZnO hexagonal wurtzite crystal structure with varying crystallite sizes. Interestingly, the films deposited on glass substrates show a high degree of texture along the (002) lattice plane. Among the (Ga-Sn) co-doped ZnO films deposited on glass substrates, the film with 1 at% Sn-Ga co-doping demonstrates the most promising results in terms of both transparency and electrical conductivity. On quartz substrates, the (Ga-Co) co-doped ZnO films with a composition of 3 at% Ga and 1 at% Co exhibit significantly enhanced optical transmittance and high electrical conductivity, making them promising candidates for optoelectronic applications. Furthermore, the (Ga-Mg) co-doping results in improved optical transmittance and high electrical conductivity for the ZnO films deposited on glass substrates with a composition of 1 at% Ga and 3 at% Mg. The observed results on cation-cation co-doped ZnO films represent an exciting and novel advancement in the field of TCO materials. The findings contribute significantly to the ongoing progress and understanding of co-doped ZnO films as efficient TCO materials for various optoelectronic applications.

The Influence of Spin Coating Speed on the Optical Properties of P3HT Thin Film

Spin coating technique has been widely used in the fabrication of thin films due to its ease of use, inexpensive processing cost and providing control over the thickness of the film. Various polymers have been used in fabricating spin-coated thin film and poly(3-hexylthiophene) (P3HT) is one of the prevalent polymers utilized due to its semiconducting properties and flexibility in processing. In this study, P3HT is deposited on pre-cleaned quartz glass by the method of spin coating. The spin coating speed is varied from 500, 1000, 1500, 2000, 2500 rpm and the optical properties of the films are characterized by using a UV-Vis spectrophotometer. The UV-Vis absorption spectra of P3HT designated absorption peaks in the range of 520 nm to 550 nm. It is shown that the absorbance of P3HT is decreased with every increment of the spinning speed. Thus revealing the dependency of P3HT thin films’ optical properties on spin coating speed.

Understanding the Effect of Deposition Technique on the Structure-Property Relationship of Polyaniline Thin Films Applied in Potentiometric pH Sensor.

The comprehension of potentiometric pH sensors with polymeric thin films for new and advanced applications is a constant technological need. The present study aimed to explore the relationship between the sensitivity and correlation coefficient of potentiometric pH sensors and the structure-property relationship of polyaniline thin films. The effect of the deposition method on the sample's properties was evaluated. Galvanostatically electrodeposited and spin-coated polyaniline thin films were used as the sensing stage. Samples were electrodeposited with a current density of 0.5 mA/cm2 for 300, 600, and 1200 s and were spin coated for 60 s with an angular velocity of 500, 1000, and 2000 rpm. The electrodeposited set of films presented higher average sensitivity, 73.4 ± 1.3 mV/pH, compared to the spin-coated set, 59.2 ± 2.5 mV/pH. The electrodeposited films presented higher sensitivity due to their morphology, characterized by a larger roughness and thickness compared to spin-coated ones, favoring the potentiometric response. Also, their oxidation state, evaluated with cyclic voltammetry and UV-VIS spectroscopy, corroborates their sensing performance. The understanding of the structure-property relationship of the polymeric films affecting the pH detection is discussed based on the characteristics of the deposition method used.

Structural Study of Diketopyrrolopyrrole Derivative Thin Films: Influence of Deposition Method, Substrate Surface, and Aging.

We report the morphology and microstructure of n-dialkyl side-chain-substituted thiophene DPP end-capped with phenyl groups (Ph-TDPP-Ph) thin films and compare the influence of deposition method and substrate surface using thermally oxidized Si and graphene substrates as well as monolayer graphene surfaces with an underlying self-assembled octadecyltrichlorosilane monolayer, complemented by an aging study of spin-coated films over a 2 weeks aging period. A distinct difference in morphology was observed between spin-coated and vacuum-deposited thin films, which formed a fiber-like morphology and a continuous layer of terraced grains, respectively. After an initial film evolution, all combinations of deposition method and substrate type result in well-ordered thin films with almost identical crystalline phases with slight variations in crystallinity and mosaicity. These findings point toward strong intermolecular forces dominating during growth, and the templating effect observed for other oligomer films formed on graphene is consequently ineffective for this material type. Upon aging of spin-coated films, a noticeable evolution involving two different morphologies and crystalline phases were observed. After several days, the thin film evolved into a more stable crystal phase and a fiber-like morphology. Moreover, slight variation in optical spectra were elucidated on the basis on density functional theory calculations. These results demonstrate that thin-film properties of DPP derivatives can be tailored by manipulating the film formation process.