Pristine P3HT Film Research Articles

Correlating dilute solvent interactions to morphology and OPV device performance

Solvent additives have been explored as a reliable way to control the morphology in bulk-heterojunction (BHJ) layers for improved device performance. We show that the choice of solvent additives has direct implications on morphological evolution, i.e. poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C61-butyric acid methyl ester (PCBM) BHJ films processed with a small amount of 1,8-diiodooctane or 1-chloronaphthalene have more crystalline PCBM domains compared to crystalline P3HT domains, while the opposite is true for films cast with nitrobenzene additive and films cast purely from chlorobenzene. The BHJ film cross-links when annealed at 300°C in the presence of 1,8-diiodooctane. Cross-linking is found to occur even in pristine P3HT and PCBM films annealed under similar conditions. NMR spectroscopy is presented as a viable technique for quantitative analysis of the amount of solvents left in the BHJ films before and after heat treatment. Despite differences in the ways the additives affect the morphology of the BHJ layer, device performance remained stable over 300h for all additives tested.

Study of Ultrathin Films of P3HT/PCBM by Means of Highly Sensitive Absorption Spectroscopy

Abstract Ultrathin films of P3HT and P3HT/PCBM prepared on glass and ITO glass substrates by spin-coating were studied by means of highly sensitive absorption spectroscopy. For pristine P3HT films, we discuss the morphology and electronic structure at the interface between the substrate and the P3HT layer. For P3HT/PCBM films, we found that phase separation could be controlled by changing the concentration of the solutions used to prepare the films.

Vertical phase separation of conjugated polymer and fullerene bulk heterojunction films induced by high pressure carbon dioxide treatment at ambient temperature

The morphology of bulk-heterojunctions (BHJ) is critically important for conjugated polymer and fullerene blend solar cells. To alter the morphology, high pressure (gas phase) carbon dioxide (CO(2)) treatment is applied to poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) blend films under ambient temperature. This process can achieve vertically phase separated morphology such that PCBM distributes toward the film surface, which is suggested by secondary ion mass spectroscopy (SIMS), contact angle, X-ray photoelectron spectroscopy (XPS) and cross-sectional scanning electron microscope (SEM) studies. While pristine P3HT films do not show a significant change upon CO(2) treatment, pristine PCBM films are plasticized in high pressure CO(2). Thus, PCBM is selectively plasticized by CO(2) in the blend film and is drawn towards the surface due to depressed surface energy, although P3HT tends to distribute around the surface without CO(2). This stratification process can enhance solar cell performance. 55% improvement is achieved in the power conversion efficiency of the CO(2) treated device compared to the untreated one, indicating that CO(2) treatment can be a good candidate for optimizing the morphology and enhancing the performance of BHJ polymer solar cells.

Organic Thin-Film Transistors Based on Blends of Poly(3-hexylthiophene) and Polystyrene with a Solubility-Induced Low Percolation Threshold

We have demonstrated that organic thin-film transistors based on blends of poly(3-hexylthiophene) (P3HT) and polystyrene (PS) with high performance and low percolation threshold can be facilely fabricated by changing the solubility of solvent and the aging time of the precursor solution. The structural analysis reveals that these benefits arise from the improvements of both the crystallinity and connectivity of P3HT phase in the blend. In the case of crystallinity, we found that because of the solubility-aging-induced formation of ordered precursors, the molecular ordering of the poly(3-hexylthiophene) phase in the blend films increases, and thus the electronic properties of field-effect transistors (FETs) based on these films are significantly improved. For the connectivity, we found that either bilayered structure or highly connected P3HT nanofibrillar network could form in the blend by changing the solubility of the solvent. Both structures are extremely beneficial to keeping connectivity of active channels and thus keeping the charge-transport properties at low semiconductor content. By optimizing the conditions, the devices based on P3HT/PS blend films containing only 1 wt % P3HT can still show field-effect mobility as high as 1 × 10−2 cm2V−1 s−1, which is comparable with that obtained from the pristine P3HT film.

A comparative study of Al and LiF:Al interfaces with poly (3-hexylthiophene) using bias dependent photoluminescence technique

The qualitative nature of the interface of poly (3-hexylthiophene) (P3HT) with Aluminum (Al) and LiF modified Aluminum (LiF:Al) has been studied using photoluminescence (PL) spectra. It was observed that coating Al on pristine P3HT film resulted in an increase in the degree of intrachain disorder. Also, a blue shift in the peak PL intensity was observed. These observations have been explained on the basis of intrachain disorder induced by the deposition of Al via thermal evaporation on P3HT film. Furthermore, bias dependence of PL spectra for ITO/P3HT/Al and ITO/P3HT/LiF:Al type Schottky cells were studied. Under the reverse bias conditions, PL quenching was found to relate directly to the depletion layer width. The increase in depletion width was found to be higher in the Al cell as compared to that of the LiF:Al cell. However, the photocurrents were higher in LiF:Al coated cells. These observed results have been explained on the basis of the difference in their respective band alignment.

Enhancement of the field-effect mobility of poly(3-hexylthiophene)/functionalized carbon nanotube hybrid transistors

With the aim of enhancing the field-effect mobility of poly(3-hexylthiophene) (P3HT) field-effect transistors (FETs), we added functionalized multiwalled carbon nanotubes (CNTs) to the P3HT solution prior to film formation. The nanotubes were found to be homogeneously dispersed in the P3HT films because of their functional groups. We found that at the appropriate CNT concentration (up to 10wt% CNT), the P3HT FETs have a high field-effect mobility of 0.04cm2V−1s−1, which is an improvement by a factor of more than 10. This remarkable increase in the field-effect mobility over that of the pristine P3HT film is due to the high conductivity of the CNTs which act as conducting bridges between the crystalline regions of the P3HT film, and the reduction in the hole-injection barrier due to the low work function of CNTs, which results in more efficient carrier injection.

Micromorphology, photophysical and electrical properties of pristine and ferric chloride doped poly(3-hexylthiophene) films

Poly(3-hexylthiophene) (P3HT), synthesized by chemical oxidative polymerization at ∼258 K, has been probed by Fourier transform infrared (FT-IR), ultraviolet–visible (UV–vis) spectroscopy, scanning electron microscopy (SEM) and by measuring the temperature dependence of DC conductivity ( σ DC) in both its pristine and partially doped state. FT-IR and UV–vis studies suggest the formation of polaronic charge species in both pristine and partially doped P3HT. SEM of pristine P3HT film exhibits the formation of randomly distributed polymer fibrils whereas ferric chloride doped P3HT film shows the formation of dopant islands (size ∼500 nm), some of which adhered to the polymer fibrils. The temperature dependence of DC conductivity in the range 77–300 K is well explained by Mott's 3-dimensional variable range hopping (3D-VRH) model.