State-of-the-art p-type doping of organic semiconductors is usually achieved by employing strong π-electron acceptors, a prominent example being tetrafl uorotetracyanoquinodimethane (F 4 TCNQ). Here, doping of the semiconducting model polymer poly(3-hexylthiophene), P3HT, using the strong Lewis acid tris(pentafl uorophenyl)borane (BCF) as a dopant, is investigated by admittance, conductivity, and electron paramagnetic resonance measurements. The electrical characteristics of BCF-and F 4 TCNQ-doped P3HT layers are shown to be very similar in terms of the mobile hole density and the doping effi ciency. Roughly 18% of the employed dopants create mobile holes in either F 4 TCNQ-or BCF-doped P3HT, while the majority of doping-induced holes remain strongly Coulomb-bound to the dopant anions. Despite similar hole densities, conductivity and hole mobility are higher in BCF-doped P3HT layers than in F 4 TCNQ-doped samples. This and the good solubility in many organic solvents render BCF very useful for p-type doping of organic semiconductors.
The mechanism and the nature of the species formed by molecular doping of the model polymer poly(3hexylthiophene) (P3HT) in its regioregular (rre-) and regiorandom (rra-) forms in solution are investigated for three different dopants: the prototypical π-electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ), the strong Lewis acid tris(pentafluorophenyl)borane (BCF), and the strongly oxidizing complex molybdenum tris[1-(methoxycarbonyl)-2-(trifluoromethyl)ethane-1,2-dithiolene] (Mo(tfd-CO 2 Me) 3 ). In a combined optical and electron paramagnetic resonance study, we show that the doping of rreP3HT in solution occurs by integer charge transfer, resulting in formation of P3HT radical cations (polarons) for all of the dopants considered here. Remarkably, despite the different chemical nature of the dopants and dopant−polymer interaction, the formed polarons exhibit essentially identical optical absorption spectra. The situation is very different for the doping of rraP3HT, where we observe formation of a charge-transfer complex with F 4 TCNQ and of a "localized" P3HT polaron on nonaggregated chains upon doping with BCF, while there is no indication of dopant-induced species in the case of Mo(tfd-CO 2 Me) 3 . We estimate the ionization efficiency of the respective dopants for the two polymers in solution and report the molar extinction coefficient spectra of the three different species. Finally, we observe increased spin delocalization in regioregular compared to regiorandom P3HT by electron nuclear double resonance, suggesting that the ability of the charge to delocalize on aggregates of planarized polymer backbones plays a significant role in determining the doping mechanism.
For molecularly doped poly(3-hexyl-thiophene) solvated individual chains can be unambiguously differentiated from aggregated ones by diagnostic polaron absorption.
Perovskite semiconductors have demonstrated outstanding external luminescence quantum yields, enabling high power conversion efficiencies (PCEs). However, the precise conditions to advance to an efficiency regime above monocrystalline silicon cells are not well understood. Herein, a simulation model that describes efficient p–i–n‐type perovskite solar cells well and a range of different experiments is established. Then, important device and material parameters are studied and it is found that an efficiency regime of 30% can be unlocked by optimizing the built‐in voltage across the perovskite layer using either highly doped (1019 cm−3) transport layers (TLs), doped interlayers or ultrathin self‐assembled monolayers. Importantly, only parameters that have been reported in recent literature are considered, that is, a bulk lifetime of 10 μs, interfacial recombination velocities of 10 cm s−1, a perovskite bandgap (
E
gap
) of 1.5 eV, and an external quantum efficiency (EQE) of 95%. A maximum efficiency of 31% is predicted for a bandgap of 1.4 eV. Finally, it is demonstrated that the relatively high mobile ion density does not represent a significant barrier to reach this efficiency regime. The results of this study suggest continuous PCE improvements until perovskites may become the most efficient single‐junction solar cell technology in the near future.
The enhancement and control of the electrical conductivity of organic semiconductors is fundamental for their use in optoelectronic applications and can be achieved by molecular doping, which introduces additional charge...
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