Filtern
Volltext vorhanden
- nein (34)
Erscheinungsjahr
Dokumenttyp
- Wissenschaftlicher Artikel (33)
- Sonstiges (1)
Sprache
- Englisch (34)
Gehört zur Bibliographie
- ja (34) (entfernen)
Schlagworte
- solar cells (2)
- Ag nanoparticles (1)
- Aggregate states (1)
- All-polymer heterojunctions (1)
- Alternating copolymers (1)
- Ambipolar charge transport (1)
- Ambipolar materials (1)
- Backbone modifications (1)
- Bilayer solar cells (1)
- Charge separation (1)
- Conformational disorder (1)
- Crystalline phases (1)
- CsPbI2Br (1)
- Donor-acceptor copolymers (1)
- Electron traps (1)
- Energetic disorder (1)
- Energy-level alignment (1)
- F(4)TCNQ (1)
- Fermi-level alignment (1)
- Fermi-level pinning (1)
- Interface dipole (1)
- Interlayer (1)
- Intrachain order (1)
- Intragap states (1)
- Kelvin probe (1)
- Microscopic morphology (1)
- Mobility imbalance (1)
- Mobility relaxation (1)
- Monte Carlo simulation (1)
- Multiple trapping model (1)
- Nonradiative recombination (1)
- OFET (1)
- Open-circuit voltage (1)
- Optoelectronic properties (1)
- Partially alternating copolymers (1)
- Photo-CELIV (1)
- Photocurrent (1)
- Photovoltaic gap (1)
- Polymer intermixing (1)
- Recombination losses (1)
- Spectral diffusion (1)
- Statistical copolymers (1)
- Stille-type cross-coupling (1)
- Structure-property relationships (1)
- Time-dependent mobility (1)
- Time-of-flight (TOF) (1)
- Transient photocurrent (1)
- Ultraviolet photoelectron spectroscopy (1)
- Vacuum-level alignment (1)
- X-ray photoelectron spectroscopy (1)
- aggregation (1)
- charge accumulation (1)
- charge injection across hybrid interfaces (1)
- charge transfer (1)
- conducting polymers (1)
- crystalline ordering (1)
- doping (1)
- efficiency potentials (1)
- electron transfer (1)
- electron-transport layers (1)
- energy-level alignments (1)
- field-effect-transistor (1)
- hybrid metal oxides (1)
- inorganic perovskites (1)
- kinetics (1)
- lead halide perovskite films (1)
- morphology (1)
- naphthalenediimide (1)
- nonradiative recombination (1)
- open-circuit voltage (1)
- organic interfaces (1)
- organic photovoltaics (1)
- organic semiconductors (1)
- organohalide lead perovskites (1)
- oxygen plasma (1)
- perovskite solar cells (1)
- phase transfer (1)
- photoluminescence (1)
- semiconducting polymers (1)
- surface band bending (1)
- surface interaction (1)
- surface photovoltage (1)
- surface states (1)
- surface wetting (1)
- thiophene (1)
- transport layer (1)
- ultraviolet photoelectron spectroscopy (1)
- voltage losses (1)
- work function (1)
Institut
A dual-characteristic polymer field-effect transistor has markedly different characteristics in low and high voltage operations. In the low-voltage range (<5 V) it shows sharp subthreshold slopes (0.3–0.4 V dec−1), using which a low-voltage inverter with gain 8 is realized, while high-voltage (>5 V) induces symmetric current with regard to drain and gate voltages, leading to discrete differential (trans) conductances.
Blending the conjugated polymer poly(3-hexylthiophene) (P3HT) with the insulating electret polystyrene (PS), we show that the threshold voltage V-t of organic field-effect transistors (OFETs) can be easily and reversely tuned by applying a gate bias stress at 130 degrees C. It is proposed that this phenomenon is caused by thermally activated charge injection from P3HT into PS matrix, and that this charge is immobilized within the PS matrix after cooling down to room temperature. Therefore, room-temperature hysteresis-free FETs with desired V-t can be easily achieved. The approach is applied to reversely tune the OFET mode of operation from accumulation to depletion, and to build inverters. (C) 2015 AIP Publishing LLC.
The optical signatures of molecular-doping induced polarons in poly(3-hexylthiophene-2,5-diyl)
(2020)
Optical absorption spectroscopy is a key method to investigate doped conjugated polymers and to characterize the doping-induced charge carriers, i.e., polarons. For prototypical poly(3-hexylthiophene-2,5-diyl) (P3HT), the absorption intensity of molecular dopant induced polarons is widely used to estimate the carrier density and the doping efficiency, i.e., the number of polarons formed per dopant molecule. However, the dependence of the polaron-related absorption features on the structure of doped P3HT, being either aggregates or separated individual chains, is not comprehensively understood in contrast to the optical absorption features of neutral P3HT. In this work, we unambiguously differentiate the optical signatures of polarons on individual P3HT chains and aggregates in solution, notably the latter exhibiting the same shape as aggregates in solid thin films. This is enabled by employing tris(pentafluorophenyl)borane (BCF) as dopant, as this dopant forms only ion pairs with P3HT and no charge transfer complexes, and BCF and its anion have no absorption in the spectral region of P3HT polarons. Polarons on individual chains exhibit absorption peaks at 1.5 eV and 0.6 eV, whereas in aggregates the high-energy peak is split into a doublet 1.3 eV and 1.65 eV, and the low-energy peak is shifted below 0.5 eV. The dependence of the fraction of solvated individual chains versus aggregates on absolute solution concentration, dopant concentration, and temperature is elucidated, and we find that aggregates predominate in solution under commonly used processing conditions. Aggregates in BCF-doped P3HT solution can be effectively removed upon simple filtering. From varying the filter pore size (down to 200 nm) and thin film morphology characterization with scanning force microscopy we reveal the aggregates' size dependence on solution absolute concentration and dopant concentration. Furthermore, X-ray photoelectron spectroscopy shows that the dopant loading in aggregates is higher than for individual P3HT chains. The results of this study help understanding the impact of solution pre-aggregation on thin film properties of molecularly doped P3HT, and highlight the importance of considering such aggregation for other doped conjugated polymers in general.
Recent advances in organic solar cell performance have been mainly driven forward by combining high-performance p-type donor-acceptor copolymers (e.g.PM6) and non-fullerene small molecule acceptors (e.g.Y6) as bulk-heterojunction layers. A general observation in such devices is that the device performance, e.g., the open-circuit voltage, is strongly dependent on the processing solvent. While the morphology is a typically named key parameter, the energetics of donor-acceptor blends are equally important, but less straightforward to access in the active multicomponent layer. Here, we propose to use spectral onsets during electrochemical cycling in a systematic spectroelectrochemical study of blend films to access the redox behavior and the frontier orbital energy levels of the individual compounds. Our study reveals that the highest occupied molecular orbital offset (Delta E-HOMO) in PM6:Y6 blends is similar to 0.3 eV, which is comparable to the binding energy of Y6 excitons and therefore implies a nearly zero driving force for the dissociation of Y6 excitons. Switching the PM6 orientation in the blend films from face-on to edge-on in bulk has only a minor influence on the positions of the energy levels, but shows significant differences in the open circuit voltage of the device. We explain this phenomenon by the different interfacial molecular orientations, which are known to affect the non-radiative decay rate of the charge-transfer state. We compare our results to ultraviolet photoelectron spectroscopy data, which shows distinct differences in the HOMO offsets in the PM6:Y6 blend compared to neat films. This highlights the necessity to measure the energy levels of the individual compounds in device-relevant blend films.
We investigate hybrid charge transfer states (HCTS) at the planar interface between a-NPD and ZnO by spectrally resolved electroluminescence (EL) and external quantum efficiency (EQE) measurements. Radiative decay of HCTSs is proven by distinct emission peaks in the EL spectra of such bilayer devices in the NIR at energies well below the bulk a-NPD or ZnO emission. The EQE spectra display low energy contributions clearly red-shifted with respect to the a-NPD photocurrent and partially overlapping with the EL emission. Tuning of the energy gap between the ZnO conduction band and a-NPD HOMO level (E-int) was achieved by modifying the ZnO surface with self-assembled monolayers based on phosphonic acids. We find a linear dependence of the peak position of the NIR EL on E-int, which unambiguously attributes the origin of this emission to radiative recombination between an electron on the ZnO and a hole on a-NPD. In accordance with this interpretation, we find a strictly linear relation between the open-circuit voltage and the energy of the charge state for such hybrid organicinorganic interfaces.
The combined effect of ultraviolet (UV) light soaking and self-assembled monolayer deposition on the work function (WF) of thin ZnO layers and on the efficiency of hole injection into the prototypical conjugated polymer poly(3-hexylthiophen-2,5-diyl) (P3HT) is systematically investigated. It is shown that the WF and injection efficiency depend strongly on the history of UV light exposure. Proper treatment of the ZnO layer enables ohmic hole injection into P3HT, demonstrating ZnO as a potential anode material for organic optoelectronic devices. The results also suggest that valid conclusions on the energy-level alignment at the ZnO/organic interfaces may only be drawn if the illumination history is precisely known and controlled. This is inherently problematic when comparing electronic data from ultraviolet photoelectron spectroscopy (UPS) measurements carried out under different or ill-defined illumination conditions.
Current models for molecular electrical doping of organic semiconductors are found to be at odds with other well-established concepts in that field, like polaron formation. Addressing these inconsistencies for prototypical systems, we present experimental and theoretical evidence for intermolecular hybridization of organic semiconductor and dopant frontier molecular orbitals. Common doping-related observations are attributed to this phenomenon, and controlling the degree of hybridization emerges as a strategy for overcoming the present limitations in the yield of doping-induced charge carriers.