Organic Semiconducting Alloys with Tunable Energy Levels

Abstract

Continuous band structure tuning, e.g., doping with different atoms, is one of the most important features of inorganic semiconductors. However, this can hardly be realized in organic semicondutors. Here, we report the first example of fine-tuning organic semiconductor band structures by alloying structurally similar derivatives into one single phase. By incorporating halogen atoms on different positions of the backbone, BDOPV derivatives with complementary intramolecular or intermolecular charge distributions were obtained. To maximize the Coloumbic attractive interactions and minimize repulsive interactions, they form antiparallel cofacial stacking in monocomponent or in alloy single crystals, resulting in efficient π orbital overlap. Benefiting from self-assembly induced solid state “olefin metathesis” reaction, it was observed, for the first time, that three BDOPV derivatives cocrystallized in one single crystal. Molecules with different energy levels serve like the dopants in inorganic semiconductors. Consequently, as the total number of halogen atoms increased, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the alloy single crystals decreased monotonously in the range from −5.94 to −6.96 eV and −4.19 to −4.48 eV, respectively.

Accurate Determination of the Minimum HOMO Offset for Efficient Charge Generation using Organic Semiconducting Alloys

“…As shown in Figure 3 a and Figure S3, Supporting Information, the HOMO energy levels of the ZITI‐N:ZITI‐S blends decrease from −5.48, −5.50, −5.52, −5.55, −5.58, −5.60, −5.63, −5.66, −5.71, −5.76, to −5.80 eV for the ZITI‐N:ZITI‐S blend with the increased ratios of ZITI‐S from 1:0, 0.9:0.1, 0.8:0.2, 0.7:0.3, 0.6;0.4, 0.5:0.5, 0.4:0.6, 0.3:0.7, 0.2:0.8, 0.1:0.9, to 0:1, respectively, while the edge shapes of the spectra are almost identical. The nearly linear correlation between the ZITI‐N:ZITI‐S ratio and HOMO level is observed, which is consistent with the proposed organic semiconducting alloy model . We also have test the LUMO and HOMO energy levels of ZITI‐N:ZITI‐S with different ratios by the cyclic voltammetry measurements.…”

“…Recently, finely tunable energy levels have been achieved with organic semiconducting alloys, [48][49][50] which are widely applied in ternary OSCs. [51][52][53][54][55][56][57][58][59][60][61] We envisioned that the alloy strategy may provide a versatile avenue to accurately establish the relationship between the HOMO offset and the exciton dissociation process.…”

Modulating Benzothiadiazole‐Based Covalent Organic Frameworks via Halogenation for Enhanced Photocatalytic Water Splitting

“…It is well-known that the charge carrier mobilities and photoelectrical conversion efficiencies in organic photovoltaics can be improved by molecular engineering of organic semiconductors through subtle structural modulations in the building blocks [28] such as halogenation (F, Cl), [29,30] variation of the substitution positions [31] and introduction of branched alkyl chains. [32] We thus rationalize that incorporating halogen atoms into COF skeletons could be a potentially effective approach for improving the photocatalytic performances of COFs.…”

Cu–Ag alloy for engineering properties and applications based on the LSPR of metal nanoparticles

“…The electronic structures of metal fundamentally determine the intra-and inter-band electronic transitions, 16 which can be adjusted by various methods, such as strain, 17 defects 18 and alloying. 19 It is interesting to investigate the role of alloy in modulating the electronic structure and optical properties of metals. 20,21 In order to examine whether alloying Au with another metal is benecial for plasmonic application, Keast et al investigated the alloys and compounds of Au with other metals by calculating the density of states (DOS), dielectric function and plasmon quality factor.…”