Post-deposition Thermal Annealing Research Articles

Annealing Temperature Effect on TeO2 Thin Films for Optical Detection Devices

Physical vapor deposition method was used for the preparation of nanostructured TeO2. Different morphologies of TeO2 are synthesized using a physical evaporation method with Te powder as the source material and quartz SiO2 as the growth substrates. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and ultraviolet-visible (UV–Vis) analyses are used to characterize the structural, morphological, and optical properties of the TeO2 products obtained. By varying the annealing temperature, different morphology of TeO2 structures is investigated. TeO2 nanostructure progress is initiated by the crystallization of particles. Different temperatures have different effects on structures, which are discussed. The films as deposited nature was amorphous; crystallization occurred at a higher annealing temperature (175 oC). With an increase in annealing temperature, the TeO2 films grain size increased. The research also points to the impact of post-deposition thermal annealing temperatures in excess of 100 °C in enhancing TeO2 film characteristics.

Raman study of apatite coating, obtained by detonation spraying of the precursor salts on the titanium substrates

The results of the Raman study of the apatite coatings, obtained by detonation spraying of the precursor salts on the titanium substrates are presented. The mixture of Ca(OH)2 and (NH4)2HPO4 salts at the molar ratio 5:3 was used as precursors. A detailed analysis of the most intense Raman band showed hydroxyapatite formation with a dominant contribution of the amorphous phase. The post-deposition thermal annealing at 640 °C for 30 min in the Ar atmosphere leads to the transformation of the amorphous hydroxylapatite into the crystalline one.

Single-Phase L10-Ordered High Entropy Thin Films with High Magnetic Anisotropy.

The vast high entropy alloy (HEA) composition space is promising for discovery of new material phases with unique properties. This study explores the potential to achieve rare-earth-free high magnetic anisotropy materials in single-phase HEA thin films. Thin films of FeCoNiMnCu sputtered on thermally oxidized Si/SiO2 substrates at room temperature are magnetically soft, with a coercivity on the order of 10Oe. After post-deposition rapid thermal annealing (RTA), the films exhibit a single face-centered-cubic phase, with an almost 40-fold increase in coercivity. Inclusion of 50 at.% Pt in the film leads to ordering of a single L10 high entropy intermetallic phase after RTA, along with high magnetic anisotropy and 3 orders of magnitude coercivity increase. These results demonstrate a promising HEA approach to achieve high magnetic anisotropy materials using RTA.

Polarized Raman Microscopy to Image Microstructure Changes in Silicon Phthalocyanine Thin‐Films

The choice of deposition technique and post deposition treatment can significantly influence the performance of organic electronic devices by altering the complex relationship between film properties and charge transport. Herein, the influence of deposition method and post deposition thermal annealing on the thin‐film properties of an emerging semiconductor, bis(tri‐n‐propylsilyl oxide) SiPc ((3PS)2‐SiPc), is examined by polarized Raman microscopy. Comparing physical vapor deposition (PVD) and spin‐coating, the orientation of (3PS)2‐SiPc molecules in films is determined and further characterized by X‐ray diffraction to assess variations in microstructure and morphology due to thermal annealing. Despite differences in film formation, non‐annealed organic thin‐film transistors (OTFTs) fabricated by PVD and spin‐coating resulted in similar electron mobilities (μe) on the order of 10−2 cm2 V−1 s−1 and threshold voltages (VT) of 10–20 V. Films fabricated by PVD annealed at 175 °C transition to a new polymorphic form with molecules aligned at a higher angle to the substrate and exhibiting reduced device performance. Conversely, spin‐coated films do not undergo any new polymorph formation or structural reorganization with thermal annealing. PVD fabricated films are thus more readily able to undergo transformations to structure and morphology with post deposition processing, while the microstructure of spin‐coated films is established at the time of deposition.

Modulating the majority charge carrier type and performance of organic heterojunction ammonia sensors by increasing peripheral fluorination of the silicon phthalocyanine sublayer

Silicon phthalocyanines (R2-SiPcs) are an emerging class of high-performance organic semiconductors which have recently found application in highly sensitive and selective bilayer organic heterojunction devices for ammonia (NH3) sensing. We report bilayer heterojunction devices based on axially-substituted bis(pentafluorophenoxy)silicon phthalocyanines of increasing peripheral fluorination ((F5PhO)2-FXSiPc) as a bottom layer and lutetium bis-phthalocyanine (LuPc2) and demonstrate how increased peripheral fluorination changes device operation from p-type to n-type in response to NH3. Sensors fabricated with (F5PhO)2-F16SiPc exhibits the smallest apparent energy barrier for interfacial charge transport by impedance spectroscopy due to better alignment of the semiconductor molecular orbitals with the semi-occupied molecular orbital of LuPc2. Bilayer heterojunction devices all demonstrated a limit of detection (LOD) below 1 ppm with (F5PhO)2-SiPc/LuPc2 yielding an LOD of 307 ppb and a sensitivity of −0.72%·ppm−1. Postdeposition thermal annealing of the (F5PhO)2-SiPc/LuPc2 device is shown to further enhance sensor performance with a 1.5-fold increase in sensitivity to −1.15%·ppm−1 and a LOD of 198 ppb.

Plasma assisted pulsed laser deposition of WO3 films for thermochromism

Tungsten trioxide (WO3) is one of the extensively investigated transition metal oxides. Its excellent chromogenic properties make WO3 promising for a variety of scientific and technological applications. We report a new method for reactively depositing WO3 films by plasma assisted pulsed laser deposition that combines electron cyclotron resonance microwave discharge and pulsed laser ablation. The plasma formed during film deposition was spectroscopically characterized by optical emission measurement, revealing that the plasma contains high density of reactive gaseous oxygen and tungsten species which are essential for efficiently synthesizing WOx precursors and depositing WO3 films. The structure of the deposited films and the effect of post-deposition thermal annealing on the film structure were characterized by X-ray diffraction and Raman spectroscopy. The as-deposited WO3 film appears amorphous in nature. Annealing resulted in the growth of crystalline grains and the improvement in the crystallinity of monoclinic WO3. Optical properties of the prepared WO3 films were studied by measuring ultraviolet–visible–near infrared transmission spectra. With the increase of annealing temperature, the WO3 films show a continuous change in color, decline in transmittance, red shift in absorption edge, and narrowing in band gap, clearly manifesting the thermochromic features of the deposited WO3 films.

Influence of Terbium Doping and Annealing on the Structural and Optical Characteristics of Sputtered Zinc Oxide Thin Films

This paper studied the structural and luminescent characteristics of undoped and doped-with-Tb3+-ions ZnO films of 200 nm and 600 nm thicknesses, grown via RF magnetron sputtering on (100) silicon substrate in Ar and Ar-O2 plasma. X-ray diffraction (XRD) patterns revealed a strong preferred orientation of ZnO and ZnO:Tb crystals of the wurtzite structure along the c-axis, perpendicular to the substrate. In the as-deposited ZnO:Tb films, the additional crystal phases, namely, Tb2O3, TbO2, and an amorphous phase, were revealed. The as-deposited undoped films were under tensile strain, that increased in the doped films. This proved the incorporation of the Tb3+ ions into the ZnO grains, and agreed with the Raman spectra investigation. The XRD data and atomic force microscopy study showed that Tb doping impeded the growth of grains and columns, respectively. The photoluminescence (PL) spectra of the doped films contained the UV band ascribed to exciton PL, a broad intrinsic defect-related band, and the narrow bands caused by the intra-shell transitions of the Tb3+ ions. Terbium doping suppressed ZnO emissions. The post-deposition rapid thermal annealing at up to 800 °C of both the undoped and doped films promoted tensile strain relaxation, grain growth, improvement in the ZnO crystal structure, and an increase in the exciton PL. The intensity of the Tb3+ PL changed non-monotonically, and was the highest for the film annealed at 600 °C. The conventional thermal annealing promoted the non-monotonic changes in the strains and grain sizes in such a way that, after annealing at 900 °C, their values became the same as in the as-deposited ZnO:Tb film. This structural change was accompanied by a decrease in the exciton and Tb3+ PL intensity. The formation of the Zn2SiO4 phase was observed via XRD, and confirmed via scanning electron microscopy. It was attributed to the interdiffusion through the film/substrate interface. The deposition in the Ar-O2 atmosphere is found to be more preferable for the formation of Tb3+ emission centers in the ZnO matrix.

Thermal annealing of superconducting niobium titanium nitride thin films deposited by plasma-enhanced atomic layer deposition

Next-generation superconducting radio frequency (SRF) cavities, based on tailored thin films, would allow for more efficient and sustainable accelerators operating at higher accelerating gradients. In particular, superconductor–insulator–superconductor (SIS) multilayers are proposed as a potential alternative to bulk Nb. In this context, NbTiN stands out as a superconducting candidate. Here, we report our studies on NbTiN thin films grown by plasma-enhanced atomic layer deposition (PEALD) in a supercycle approach on AlN in situ deposited on planar silicon substrates. In detail, different ternary compound compositions and thicknesses have been investigated concerning the elemental composition, the superconducting properties, and the crystallinity of the deposited thin films. Two different post-deposition thermal treatments have been applied to Nb0.75Ti0.25N thin films of different thicknesses. Their effect on the film properties has been evaluated. It has been demonstrated that an optimized post-deposition thermal annealing procedure significantly improves the quality of our PEALD deposited Nb0.75Ti0.25N thin films, achieving the highest superconducting critical temperature (Tc) of 15.9 K obtained for films deposited by atomic layer deposition (ALD) so far and a lower critical field (Hc1) of 213 mT, which overpasses the bulk Nb intrinsic limit of 200 mT. Our studies are a promising first stepping stone on the path toward tailored thin films based SRF cavities.

Low-temperature synthesis of crystalline vanadium oxide films using oxygen plasmas

Vanadium oxide (VOx) compounds feature various polymorphs, including V2O5 and VO2, with attractive temperature-tunable optical and electrical properties. However, to achieve the desired material property, high-temperature post-deposition annealing of as-grown VOx films is mostly needed, limiting its use for low-temperature compatible substrates and processes. Herein, we report on the low-temperature hollow-cathode plasma-enhanced atomic layer deposition (ALD) of crystalline vanadium oxide thin films using tetrakis(ethylmethylamido)vanadium and oxygen plasma as a precursor and coreactant, respectively. To extract the impact of the type of plasma source, VOx samples were also synthesized in an inductively coupled plasma-enhanced ALD reactor. Moreover, we have incorporated in situ Ar-plasma and ex situ thermal annealing to investigate the tunability of VOx structural properties. Our findings confirm that both plasma-ALD techniques were able to synthesize as-grown polycrystalline V2O5 films at 150 °C. Postdeposition thermal annealing converted the as-grown V2O5 films into different crystalline VOx states: V2O3, V4O9, and VO2. The last one, VO2 is particularly interesting as a phase-change material, and the metal-insulator transition around 70 °C has been confirmed using temperature-dependent x-ray diffraction and resistivity measurements.

Spongy TiO2 layers deposited by gig-lox sputtering processes: Contact angle measurements

The use of nanostructured materials is increasingly widespread thanks to their particular properties that can improve the performance of devices in various scientific applications. One of them is in the architecture of perovskite solar cells characterized by high photoconversion efficiency values that make them able to compete with silicon solar cells. In this framework, we deposited TiO2 sponges by reactive sputtering based on a grazing-incidence geometry combined with the local oxidation of species. The deposited material gains 50% porosity in volume through depths of hundreds of nanometers and consists of a forest of uniform rods separated by mesopores (pipelines) arising from the grazing geometry. Many previous studies showed how TiO2 can improve the efficiency of perovskite solar cells. In this article, we investigated the change of the wettability values of the TiO2 samples before and after a postdeposition thermal annealing treatment. For comparison, the influence of the annealing on the wettability of the glass substrate is also reported.

Achieving a high energy storage density in Ag(Nb,Ta)O 3 antiferroelectric films via nanograin engineering

Due to its lead-free composition and a unique double polarization hysteresis loop with a large maximum polarization (<i>P</i>_max) and a small remnant polarization (<i>P</i>_r), AgNbO₃-based antiferroelectrics (AFEs) have attracted extensive research interest for electric energy storage applications. However, a low dielectric breakdown field (<i>E</i>_b) limits an energy density and its further development. In this work, a highly efficient method was proposed to fabricate high-energy-density Ag(Nb,Ta)O₃ capacitor films on Si substrates, using a two-step process combining radio frequency (RF)-magnetron sputtering at 450 ℃ and post-deposition rapid thermal annealing (RTA). The RTA process at 700 ℃ led to sufficient crystallization of nanograins in the film, hindering their lateral growth by employing short annealing time of 5 min. The obtained Ag(Nb,Ta)O₃ films showed an average grain size (<i>D</i>) of ~14 nm (obtained by Debye–Scherrer formula) and a slender room temperature (RT) polarization–electric field (<i>P–E</i>) loop (<i>P</i>_r ≈ 3.8 μC·cm⁻² and <i>P</i>_max ≈ 38 μC·cm⁻² under an electric field of ~3.3 MV·cm⁻¹), the <i>P–E</i> loop corresponding to a high recoverable energy density (<i>W</i>_rec) of ~46.4 J·cm⁻³ and an energy efficiency (<i>η</i>) of ~80.3%. Additionally, by analyzing temperature-dependent dielectric property of the film, a significant downshift of the diffused phase transition temperature (<i>T</i>_M2–M3) was revealed, which indicated the existence of a stable relaxor-like AFE phase near the RT. The downshift of the <i>T</i>_M2–M3 could be attributed to a nanograin size and residual tensile strain of the film, and it led to excellent temperature stability (20–240 ℃) of the energy storage performance of the film. Our results indicate that the Ag(Nb,Ta)O₃ film is a promising candidate for electrical energy storage applications.

Influence of rapid thermal annealing time on physical properties of Mg and F co-doped ZnO thin films deposited by radio frequency magnetron sputtering

• Mg-F co-doped ZnO (MFZO) thin films are deposited by magnetron sputtering. • Conductivity of MFZO films increases by 37% after the rapid thermal annealing. • The average visible transmittances of the annealed MFZO films exceed 93%. • The annealed MFZO film achieves a high figure of merit (FOM) of 1.18 × 10-2 Ω-1. • The high-FOM MFZO thin films could be used as transparent conducting films. Transparent conducting oxides are commonly used in flat-panel displays, solar cells, light emitting diodes, and other optoelectronic devices. In this study, transparent conducting Mg and F co-doped ZnO (MFZO) thin films were prepared by using radio frequency magnetron sputtering and a post-deposition rapid thermal annealing (RTA) was carried out at 400°C in vacuum. To study the influence of RTA on structural, electrical, and optical properties of the MFZO thin films, the RTA processing time is varied (0–120 s). X-ray diffraction analysis showed that the co-doping of 3.0 at% Mg and 6.0 at% F did not change the (0 0 2) oriented hexagonal wurtzite structure of the MFZO films, while the RTA process effectively improved its crystal quality. The intensity and full width at half maximum of the (0 0 2) peaks revealed that the MFZO films had the optimum crystallinity at the RTA time of 15–60 s and the largest grain size at the RTA time of 30 s. Under this optimal RTA condition, the electrical conductivity increased by 37%, reaching the optimum Hall mobility of 12.5 cm 2 /Vs, carrier concentration of 3.94 × 10 20 cm −3 , and resistivity of 1.27 × 10 −3 Ω cm. The average total transmittance in the visible region (380 – 780 nm) increased to more than 93% at the RTA duration of 15–60 s, and then decreased for a longer RTA time. The optical band gap, determined from the absorption edge of transmittance using Tauc plot, increased from 3.745 to 3.798 eV after RTA for 30 s. The figure of merit (FOM) of the MFZO film increased by 52% to 1.18 × 10 −2 Ω −1 . Thanks to the use of appropriate dopants and RTA process, this high FOM is much superior to previous research results on MFZO thin films with FOMs ranging from 10 −6 to 10 −3 Ω −1 . This work provides a fast and low-temperature approach to realize high-FOM MFZO thin films to fulfill the requirements of a transparent electrode in optoelectronic devices.

Time-resolved terahertz spectroscopy for probing the effects of low-temperature annealing on CsPbBr3 evaporated thin-films

The fine-tuning of the growth conditions and post-deposition treatments is of fundamental importance to improve the efficiency of photovoltaic devices based on all-inorganic metal halide perovskites like CsPbBr3. In this work, we used time-resolved terahertz spectroscopy (TRTS) in combination with optical characterization techniques, x-ray diffraction (XRD), and scanning electron microscopy, to probe the different properties induced by a low-temperature (180 °C) annealing treatment on evaporated CsPbBr3 thin-films. We observed a faster build-up and relaxation dynamics in the annealed sample, accompanied by a remarkable decrease of the photoluminescence intensity and minor changes in the photoconductivity and XRD measurements as compared to the as-deposited sample. We estimated for both the samples a mobility of cm2 V−1 s−1. Our results suggest that the lattice reorganization induced by low-temperature annealing of evaporated CsPbBr3 could lead to a different charge carrier-phonon coupling and to an increased contribution of non-radiative recombination channels. We found that TRTS can be effectively used to follow the changes induced by post-deposition thermal annealing of CsPbBr3.

Effect of thermal annealing on dielectric and ferroelectric properties of aerosol-deposited 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 thick films

In this work, the effects of thermal annealing at 500 °C on aerosol-deposited 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 thick films on stainless-steel substrates are investigated using two complementary methods at high and low applied external electric fields. The first one is the positive up negative down method, which allows us to obtain information about the switching and non-switching contributions to the polarization. It shows that the as-deposited film is ferroelectric before annealing, since it has a switching contribution to the polarization. After annealing, both the switching and non-switching contributions to polarization increased by a factor of 1.6 and 2.33, respectively, indicating a stronger ferroelectric behavior. The second method is based on impedance spectroscopy coupled with Rayleigh analysis. The results show that post-deposition thermal annealing increases the reversible domain wall contribution to the dielectric permittivity by a factor of 11 while keeping the threshold field similar. This indicates that, after annealing, domain wall density is larger while domain wall mobility remains similar. These two complementary characterization methods show that annealing increases the ferroelectric behavior of the thick film by increasing the domain wall density, and its influence is visible both on polarization vs electric field loop and dielectric permittivity.

N-type amorphous silicon-germanium thin films with embedded nanocrystals as a novel thermoelectric material of elevated ZT

The state-of-art thermoelectric (TE) materials with high efficiency (i.e., ZT ~ 1) at room temperature require meeting essential features, such as being environmentally friendly (i.e., avoiding the use of rare and toxic elements), cheap to produce, and high ZT. However, the enhancement of ZT has always been a challenge because the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature are interdependent. In this work, we report the fabrication of amorphous silicon-germanium (a-SiGe) thin films deposited by low-frequency plasma-enhanced chemical vapor deposition (LF-PECVD) with embedded nanocrystals that have a ZT of 2.61 at room temperature. The above is achieved by enhancing the thermoelectric power factor and, simultaneously, keeping the lowest thermal conductivity; both are in concordance with the phonon-glass electron-crystal (PGEC) approach. The power factor enhancement is accomplished by increasing the electrical conductivity through N-type doping and an annealing process at 500 °C to which thin films were subjected to improve their transport properties while avoiding crystallization. Therefore, the room-temperature electrical conductivity increased two orders of magnitude from 1.11E-01 up to 42.79 S/cm. In addition, the growth of nanocrystals (5–15 nm) embedded into the amorphous matrix contribute to the transport of charge carriers. The measured thickness and Seebeck coefficient of thin films were 200 nm and −1.038 mV/K, respectively. On the other side, the lowest thermal conductivity is reached because the material’s amorphous phase is kept despite the applied post-deposition thermal annealing. The experimental value for thermal conductivity was 0.53 W/m·K, almost half of the minimum thermal conductivity proposed by Slack. In summary, the structural characterization (developed by X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy) shows that a-SiGe material not only has an amorphous phase despite the applied thermal annealing, but it also possesses nanocrystals, which is demonstrated by transmission electron microscopy in high-resolution mode. Therefore, the a-SiGe material obtained in this research is proposed as a novel and potential thermoelectric material because it has optimized TE properties and meets desirable features, such as being inexpensive, non-hazardous, and environmentally friendly for energy harvesting applications.

Effect of pH variation and annealing on covalently assembled nanodiamond films

This work examines the effect of using low-ionic strength zwitterionic buffer and post-deposition thermal annealing on the microstructure and thermal conductivity of continuous nanocrystalline diamond films that are deposited via the directed covalent assembly of detonation nanodiamonds. Variation of the zwitterionic buffer pH was found to tune the surface coverage, film thickness, thermal conductivity, and film morphology as quantified by apparent porosity and pore size distribution. The sequential annealing of these films up to 400 °C, showed the anticipated severance of amide bonds holding the nanodiamonds together, followed by the detrimental aggregation of the nanodiamonds to segregated islands, losing film continuity and increasing apparent porosity. The change in thermal conductivity with annealing was subjective to buffer pH, suggesting that the morphology changes associated with annealing may have a complex relationship with thermal conductivity. The thermal conductivity data were further analyzed using a phonon hopping model to quantify the degree of phonon movement across boundaries. Overall, the results demonstrate a way to achieving porous, low-cost nanocrystalline diamond thin films with tunable film morphology and thermal conductivity.

Influence of Nitrogen on the Luminescence Properties of Ce-Doped SiOxNy

We report wideband photoluminescent emission from cerium-doped silicon oxynitride (Ce-doped SiOxNy) thin films deposited using electron cyclotron resonance plasma enhanced chemical-vapor deposition (ECR-PECVD). The in situ doping with Cerium (Ce) was performed using a volatile metal organic powder, (Ce[tmhd]4). Oxygen was gradually substituted by nitrogen to produce SiOxNy thin films with varying nitrogen to oxygen ratio, to explore the effect of nitrogen on the photoluminescence (PL) of the thin films. Thin film composition and optical constants were determined using Rutherford back scattering and ellipsometry techniques, respectively. Samples subjected to post-deposition thermal annealing yielded considerably stronger blue/white PL emission than as-deposited ones, due to the formation of Ce-containing clusters at a temperature of 1000 °C and above. X-ray diffraction (XRD) revealed no crystalline structure in samples annealed at elevated temperatures. The optimum layer composition and annealing condition to produce SiOxNy thin films with maximized Ce3+ emission was determined. Besides, hydrogen fluoride etching along with hydrogen passivation demonstrated the enhancement of the PL emission of the thin films.

Annealing Impact on the Evolution of Crystalline Phases and Emission in Si-Rich HfO2:Nd Films Obtained By Magnetron Sputtering

Hafnium oxide films doped with Si and Nd atoms have been produced by radio-frequency magnetron sputtering in pure argon plasma followed by an annealing in nitrogen atmosphere for 1-60 minutes at the temperature 1000 °C. The effect of post-deposition thermal annealing on the transformation of crystalline phases and photoluminescence spectra was investigated by the non-destructive methods (scanning electronic microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman scattering and photoluminescence(PL)). The XRD analysis of these samples demonstrate the phase separation process which depends on the time range and the annealing temperature. In the studed samples, the formation of the tetragonal HfO2, tetragonal SiO2 and cubic Si phases was observed by XRD and confirmed by the Raman study. Thermal annealing influents also on PL spectra where the main bands were detected at 380, 450, 550, 780 and 880 nm. The emission and excitation mechanisms for the Nd radiative defects, and the impact of phase transformation in studied films, are analyzed and discussed.

Structure and Emission Evolution in Si-Rich HfO2:Pr Films Versus Annealing Temperature

Pr-doped Si-rich-HfO2 films with specific emitting and structural properties have been prepared by radio-frequency magnetron sputtering using standard pure argon plasma approach. The effect of post-deposition thermal annealing on the transformation of crystalline phases, their compositions and photoluminescence spectra was investigated by means of the Energy Dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), scanning electronic microscopy (SEM), Raman scattering and photoluminescence (PL) methods. Thermal annealing was carried out at 800 °C, 900 °C, 1000 °C and 1100 °C within time of 30 min in nitrogen atmosphere. The SEM images demonstrate the grains with the size about 40 nm. It was observed that the influence of temperature at annealing causes the phase transformation and separation processes. In studied samples, the formation of the tetragonal HfO2 and SiO2 phases, were detected at XRD study after the annealing at 1000 and 1100 °C. PL spectra of these films are complex and demonstrate several PL bands centered at 442, 479, 523, 607, 637 and 716 nm. Their contribution depends on the annealing temperature and governs the shape of total PL spectra. The impact of crystalline phase separation on the peculiarities of PL spectra and XRD are analyzed and discussed.

Role of Postdeposition Thermal Annealing on Intracrystallite and Intercrystallite Structuring and Charge Transport in Poly(3-hexylthiophene)

The performance of electronic devices comprising conjugated polymers as the active layer depends not only on the intrinsic characteristics of the materials but also on the details of the extrinsic processing conditions. In this study, we examine the effect of postdeposition thermal treatments on the microstructure of poly(3-hexylthiophene) (P3HT) thin films and its impact on their electrical properties. Unsurprisingly, we find thermal annealing of P3HT thin films to generally increase their crystallinity and crystallite coherence length while retaining the same crystal structure. Despite such favorable structural improvements of the polymer active layers, however, thermal annealing at high temperatures can lead to a net reduction in the mobility of transistors, implicating structural changes in the intercrystallite amorphous regions of these semicrystalline active layers take place on annealing, and the simplistic picture that crystallinity governs charge transport is not always valid. Our results instead suggest tie-chain pullout, which occurs during crystal growth and perfection upon thermal annealing to govern charge transport, particularly in low-molecular-weight systems in which the tie-chain fraction is low. By demonstrating the interplay between intracrystallite and intercrystallite structuring in determining the macroscopic charge transport, we shed light on how structural evolution and charge-transport properties of nominally the same polymer can vary depending on the details of processing.