In the present work, we present the first demonstration to tune the work function of polyaniline by controlling the concentration level of camphorsulfonic acid as a protonic acid dopant and m-cresol as a solvent. Optical, thermal, structural, and electronic properties, along with surface topography and elemental analysis of protonated polyaniline, were studied in detail to investigate the effect of camphorsulfonic acid on the work function of polyaniline. Results showed that an increase in camphorsulfonic acid content induces a gradual transformation in polyaniline structure from an emeraldine base to an emeraldine salt phase, which is associated with an increase in electrical conductivity and an improvement in crystallinity. X-ray photoelectron spectroscopy was used to evaluate the work function and to determine the elemental composition of the surface and several atomic layers beneath the surface. Results showed that raising camphorsulfonic acid content from quarter protonated to fully protonated leads to an increase in the work function of polyaniline from 4.42 ±0.14 eV to 4.78 ±0.13 eV, respectively.
In this work, polyaniline (PANI) protonated with various levels of camphor sulfonic acid (HCSA) has been used as a hole‐transport layer (HTL) in organic bulk‐heterojunction solar cells. Polyaniline with three different protonation levels was inserted between poly(3‐hexylthiophene‐2,5‐diyl):[6,6]‐phenyl‐C61‐butyric acid methyl ester (P3HT:PCBM) and the indium‐tin oxide (ITO) glass transparent electrode to explore the effects of varying the protonation level to optimize the hole‐transport properties. The three protonation concentrations (in molar ratios) of PANI are zero‐protonated (PANI/HCSA, 1:0), half‐protonated (PANI/HCSA, 1:1), and fully protonated (PANI/HCSA, 1:2) thin films. Current–voltage measurements under AM 1.5 conditions revealed that a conversion efficiency of 1.3 % was achieved if half‐protonated PANI was used as the HTL. Several analytical methods were utilized for characterizing PANI to understand the effects of the protonation level on the electrical, optoelectronic, and structural characteristics, and their correlation with final device properties.
Poly(3-hexylthiophene) (P3HT)-graphene nanocomposites were synthesized via in situ oxidative polymerization of 3-hexylthiophene monomer in the presence of graphene. The main thrust was to investigate the structural and optoelectronic properties of P3HT-graphene nanocomposites with various graphene concentrations. NMR spectroscopy was used to determine the regioregularity of the polymer composites, whereas Fourier transform infrared spectroscopy and differential scanning calorimetry were used to study their structural and thermal properties. Moreover, cyclic voltammetry was employed to evaluate the HOMO levels of the nanocomposites, while optical spectrophotometry (UV-Vis-NIR) was utilized to determine the optical bandgap of the composites. The information from the aforementioned techniques was used to estimate the HOMO-LUMO energy levels. The results revealed changes in the optical bandgap of P3HT with increasing graphene content. Furthermore, an extensive study aiming at the effect of graphene content on the optical constants of P3HT was conducted using ellipsometry. Photoluminescence analysis of the samples showed no quenching effect of photoluminescence emission with increasing graphene content. Our studies indicate that the inclusion of graphene impacts the optoelectronic properties of P3HT, which can further be used for advanced applications, such as organic solar cells, organic light emitting diodes, organic field-effect transistors, and polymer batteries.
PSS-based cells exhibited faster degradation than PANI:CSA-based cells, where the average efficiency of six cells dropped to zero in less than one and a half years. On the other hand, PANI:CSA-based cells exhibited a much more stable performance with an average efficiency drop of only 15% of their initial values after one and a half years and 63% after two years. A single-diode model was utilized to fit the experimental data with the theoretical curve to extract the diode parameters, such as the ideality factor, to explain the effect of aging on the diode's performance.
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