Synergistic Effects of Processing Additives and Thermal Annealing on Nanomorphology and Hole Mobility of Poly(3-hexylthiophene) Thin Films

Abstract

Control of the nanoscale molecular ordering and charge-carrier mobility of poly(3-hexylthiophene-2,5-diyl) (P3HT) was achieved by the combined use of processing additives and thermal annealing. Evaluation of four processing additives (1,8-octanedithiol (ODT), diphenyl ether (DPE), 1-chloronaphthalene (CN), and 1,8-diiodooctane (DIO), which are commonly used for the fabrication of organic solar cells, revealed that the nanoscale molecular ordering and, therefore, the charge-carrier mobility, are largely affected by the additives, as demonstrated by spectral absorption, X-ray diffraction, and atomic force microscopy. Thermal annealing selectively influenced the morphological changes, depending on the solubility of P3HT in the additive at high temperature. In the case of CN, in which P3HT can be dissolved at moderate temperature, significant molecular ordering was observed even without thermal annealing. For DIO, in which P3HT is only soluble at elevated temperature, the mobility reached 1.14 × 10−1 cm2 V−1 s−1 only after annealing. ODT and DPE were not effective as processing additives in a single-component P3HT. This study provides insight for designing the processing conditions to control the morphology and charge-transport properties of polymers.

Differing Impacts of Blended Fullerene Acceptors on the Performance of Ternary Organic Solar Cells

“…We note that the data also show the positive impact of DIO of EQE in both P3HT- and PTB7-based blends in agreement with the literature. ,− In the case of P3HT-based blends, DIO has been shown to improve the formation of P3HT fibrils, , in agreement with TEM and AFM images in Figure . By contrast, PTB7-based blends are improved by the addition of DIO, as it limits the size of PCBM aggregates that would otherwise reduce exciton dissociation. , Again, our AFM and TEM analysis in Figure is in agreement with these literature data; however, we additionally show that DIO also suppresses the size of ICBA aggregates more generally.…”

Selective Ammonia-Sensing Platforms Based on a Solution-Processed Film of Poly(3-Hexylthiophene) and p-Doping Tris(Pentafluorophenyl)Borane

“…In the pristine P3HT device, the drain current (Id) linearly increased with the drain voltage (Vd) in the linear region, and then saturated at higher drain voltages owing to the pinch-off of the charge accumulation layer. The pure P3HT exhibited a field-effect mobility (μ), current on/off ratio (Ion/Ioff), and threshold voltage (VT) of 0.018 (±0.0028) cm 2 V −1 s −1 , >3.3 × 10 4 , and −23.4 (±1.7) V, respectively, which are in the typical ranges for P3HT devices [22,37]. Figure 1d,e shows UV-vis absorption spectra of the blends, in both solutions and thin films.…”

Selective Wet-Etching of Polymer/Fullerene Blend Films for Surface- and Nanoscale Morphology-Controlled Organic Transistors and Sensitivity-Enhanced Gas Sensors

“…We first spin-coated the polymer and blends dissolved in chloroform, resulting in the polymer films with the thickness ranging ~50–110 nm. Since a processing additive such as DIO is known to affect the morphology of polymer and polymer:PCBM blends, we prepared the blend both with and without DIO [42,43,44,45,46,47]. Our hypothesis was that, with DIO known to enhance the phase separation of the P3HT:PCBM mixtures and form PCBM agglomerates in polymer solar cells, the selective solvent can easily access the PCBM clusters and remove them from the polymer matrix [40].…”

“…Comparing the blend films processed without and with DIO, the addition of a processing additive resulted in larger intensities of shoulders at 550 nm and 600 nm, relative the corresponding peak at 500 nm. These more prominent shoulders in the P3HT signal with the addition of DIO suggest a higher degree of interaction between P3HT molecules [47].…”