Search

Poly(3‐hexyl‐thiophene‐2,5‐diyl) (P3HT) is one of the most commonly used materials in organic electronics, yet it is considered to be rather unattractive for organic field‐effect transistors (OFETs) due to its tendency to oxidize under aerobic conditions. Strong p‐doping of P3HT by oxygen causes high off‐currents in such devices opposing the desired high on/off‐ratios. Herein, a new application‐oriented method involving the recently developed immobilizable organic n‐dopant 2‐(2‐((4‐azidobenzyl)oxy)phenyl)‐1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol (o‐AzBnO‐DMBI) is presented allowing to process and operate P3HT OFETs in air. The n‐dopants compensate oxygen doping by trapping generated free holes, thereby rediminishing OFET off‐currents by approximately two orders of magnitude. At the same time, field‐effect mobilities remain high in the order of up to 0.19 cm2 V−1 s−1. Due to the covalent attachment of the dopants to the host matrix after photochemical activation, a drift of the otherwise mobile ions within the device is prevented even at high operating voltages and, thus, hysteresis in the corresponding transfer characteristics is kept low. In this manner, the air instability of P3HT OFETs is successfully resolved paving an auspicious way toward OFET mass production. As the immobilization process employed here is nonspecific with respect to the host material, this strategy is transferable to other p‐type semiconductors. [ABSTRACT FROM AUTHOR]

Intrinsic organic -- inorganic metal halide perovskites (OIHP) based semiconductors have shown wide applications in optoelectronic devices. There have been several attempts to incorporate heterovalent metal (e.g., Bi[sup 3+]) ions in the perovskites in an attempt to induce electronic doping and increase the charge carrier density in the semiconductor. It has been reported that inclusion of Bi[sup 3+] decreases the band gap of the material considerably. However, contrary to the earlier conclusions, despite a clear change in the appearance of the crystal as observed by eye, here we show that the band gap of MAPbBr[sub 3] crystals does not change due the presence of Bi[sup 3+] in the growth solution. An increased density of states in the band gap and use of very thick samples for transmission measurements, erroneously give the impression of a band gap shift. These sub band gap states also act as nonradiative recombination centers in the crystals. [ABSTRACT FROM AUTHOR]

Here we present the controlled deposition of highly aligned poly(3-hexylthiophene-2,5-diyl) (P3HT) fibers by inkjet printing. The functional ink consists of the crystallization agent 1,3,5-trichlorobenzene (TCB), the carrier solvent chlorobenzene, and the semiconducting polymer P3HT. The inkjet printing process was designed in such a way that the drying zone migrates in the printing direction, effectively growing the TCB out of solution and forcing the P3HT chains to align in the printing direction. The films are deposited in arbitrary shapes on a variety of substrates, thus demonstrating the full freedom of design necessary for the digital fabrication of future integrated circuits. We demonstrate by optical and structural investigations that P3HT arranges in a nontrivial empty-core-shell structure with the long molecular axis in the fiber direction while the short axis extends in a radial fashion. Such arrangement induces a fourfold increase in field-effect mobility along the fiber direction as compared to the isotropic printed reference. [ABSTRACT FROM AUTHOR]

Three-dimensional lead-halide perovskites have attracted a lot of attention due to their ability to combine solution processing with outstanding optoelectronic properties. Despite their soft ionic nature these materials demonstrate a surprisingly low level of electronic disorder resulting in sharp band edges and narrow distributions of the electronic energies. Understanding how structural and dynamic disorder impacts the optoelectronic properties of these perovskites is important for many applications. Here we combine ultrafast two-dimensional vibrational spectroscopy and molecular dynamics simulations to study the dynamics of the organic methylammonium (MA) cation orientation in a range of pure and mixed trihalide perovskite materials. For pure MAPbX3 (X = I, Br, Cl) perovskite films, we observe that the cation dynamics accelerate with decreasing size of the halide atom. This acceleration is surprising given the expected strengthening of the hydrogen bonds between the MA and the smaller halide anions, but can be explained by the increase in the polarizability with the size of halide. Much slower dynamics, up to partial immobilization of the organic cation, are observed in the mixed MAPb(ClxBr1-x)3 and MAPb(BrxI1-x)3 alloys, which we associate with symmetry breaking within the perovskite unit cell. The observed dynamics are essential for understanding the effects of structural and dynamical disorder in perovskite-based optoelectronic systems. [ABSTRACT FROM AUTHOR]

Efficient electrical doping of organic semiconductors is a necessary prerequisite for the fabrication of high performance organic electronic devices. In this work, we study p-type doping of poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) spin-cast from two different solvents. Using electron diffraction, we find strong dopant-induced π-π-stacking for films from the solvent chloroform, but not from chlorobenzene. This image is confirmed and expanded by the analysis of vibrational features of P3HT and polaron absorptions using optical spectroscopy. Here, a red-shifted polaron absorption is found in doped films from chloroform, caused by a higher conjugation length of the polymer backbone. These differences result in a higher conductivity of films from chloroform. We use optical spectroscopy on the corresponding blend solutions to shed light on the origin of this effect and propose a model to explain why solutions of doped P3HT reveal more aggregation of charged molecules in chlorobenzene, whereas more order is finally observed in dried films from chloroform. Our study emphasizes the importance of solvent parameters exceeding the bare solubility of pure dopant and host material for the preparation of highly conductive doped films. [ABSTRACT FROM AUTHOR]

In this work we examine small conjugatedmolecules bearing a thiolheadgroup as self assembled monolayers (SAM). Functional groups inthe SAM-active molecule shift the work function of gold to n-channelsemiconductor regimes and improve the wettability of the surface.We examine the effect of the presence of methylene linkers on theorientation of the molecule within the SAM. 3,4,5-Trimethoxythiophenol(TMP-SH) and 3,4,5-trimethoxybenzylthiol (TMP-CH2-SH) werefirst subjected to computational analysis, predicting work functionshifts of −430 and −310 meV. Contact angle measurementsshow an increase in the wetting envelope compared to that of pristinegold. Infrared (IR) measurements show tilt angles of 22 and 63°,with the methylene-linked molecule (TMP-CH2-SH) attaininga flatter orientation. The actual work function shift as measuredwith photoemission spectroscopy (XPS/UPS) is even larger, −600and −430 meV, respectively. The contact resistance betweengold electrodes and poly[N,N′-bis(2-octyldodecyl)-naphthalene-1,4:5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene) (Polyera AktiveInk, N2200) in n-type OFETs is demonstrated to decrease by 3 ordersof magnitude due to the use of TMP-SH and TMP-CH2-SH. Theeffective mobility was enhanced by two orders of magnitude, significantlydecreasing the contact resistance to match the mobilities reportedfor N2200 with optimized electrodes. [ABSTRACT FROM AUTHOR]

We present a comparison of the potential distribution along the cross section of bilayer poly(3-hexylthiophene)/1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 (P3HT/PCBM) solar cells, which show normal and anomalous, S-shaped current-voltage (IV) characteristics. We expose the cross sections of the devices with a focussed ion beam and measure them with scanning Kelvin probe microscopy. We find that in the case of S-shaped IV-characteristics, there is a huge potential drop at the PCBM/Al top contact, which does not occur in solar cells with normal IV-characteristics. This behavior confirms the assumption that S-shaped curves are caused by hindered charge transport at interfaces. [ABSTRACT FROM AUTHOR]