Monolayer Phases of a Dipolar Perylene Derivative on Au(111) and Surface Potential Build-Up in Multilayers.

9-(Bis-p-tert-octylphenyl)-amino-perylene-3,4-dicarboxy anhydride (BOPA-PDCA) is a strongly dipolar molecule representing a group of asymmetrically substituted perylenes that are employed in dye-sensitized solar cells and hold great promise for discotic liquid crystal applications. Thin BOPA-PDCA films with orientated dipole moments can potentially be used to tune the energy-level alignment in electronic devices and store information. To help assessing these prospects, we here elucidate the molecular self-assembly and electronic structure of BOPA-PCDA employing room temperature scanning tunneling microscopy and spectroscopy in combination with ultraviolet and X-ray photoelectron spectroscopies. BOPA-PCDA monolayers on Au(111) exclusively form in-plane antiferroelectric phases. The molecular arrangements, the increase of the average number of molecules per unit cell via ripening, and the rearrangement upon manipulation with the STM tip indicate an influence of the dipole moment on the molecular assembly and the rearrangement. A slightly preferred out-of-plane orientation of the molecules in the multilayer induces a surface potential of 1.2 eV. This resembles the giant surface potential effect that was reported for vacuum-deposited tris(8-hydroxyquinoline)aluminum and deemed applicable for data storage. Notably, the surface potential in the case of BOPA-PDCA can in part be reversibly removed by visible light irradiation.

Self-assembly, dynamics, and phase transformation kinetics of donor-acceptor substituted perylene derivatives.

The role of alkyl chain substitution on the phase formation and core dynamics is studied in a series of diphenylamine functionalized perylenemonoimides (PMIs), by X-ray scattering, calorimetry and site-specific solid-state NMR techniques. In addition, the strong dipole associated with the donor-acceptor character of the molecules allow an investigation of the dynamics with dielectric spectroscopy. The self-assembly revealed an ordered phase only in PMIs with branched alkyl chains. This phase comprises a helical stacking of molecules with a molecular twist angle of 60 degrees. Results from solid-state NMR further pointed out the importance of intramolecular hydrogen bonding in stabilizing the intracolumnar packing within the ordered phase. Moreover, the core dynamics are frozen as revealed by the value of the dynamic order parameters and the reduced strength of dipolar relaxation. The kinetics of phase transformation from the isotropic to the ordered phase proceeds via a nucleation and growth mechanism, and the rates are dominated by the nucleation barrier. Within the isotropic phase the core dynamics display strong temperature dependence with rates that depend on the number of methylene units in the alkyl chains.

Enhancing Thermal Stability and Lifetime of Solid-State Dye-Sensitized Solar Cells via Molecular Engineering of the Hole-Transporting Material Spiro-OMeTAD.

Thermal stability of hybrid solar cells containing spiro-OMeTAD as hole-transporting layer is investigated. It is demonstrated that fully symmetrical spiro-OMeTAD is prone to crystallization, and growth of large crystalline domains in the hole-transporting layer is one of the causes of solar cell degradation at elevated temperatures, as crystallization of the material inside the pores or on the interface affects the contact between the absorber and the hole transport. Suppression of the crystal growth in the hole-transporting layer is demonstrated to be a viable tactic to achieve a significant increase in the solar cell resistance to thermal stress and improve the overall lifetime of the device. Findings described in this publication could be applicable to hybrid solar cell research as a number of well-performing architectures rely heavily upon doped spiro-OMeTAD as hole-transporting material.

Perylene imides for organic photovoltaics: yesterday, today, and tomorrow.

Perylene imides have been an object of research for 100 years and their derivatives are key n-type semiconductors in the field of organic electronics. While perylene diimides have been applied in many electronic and photonic devices, their use can be traced back to the first efficient organic solar cell. By functionalizing different positions of the in total 12 positions (four peri, four bay, and four ortho-positions) on the perylene core, perylene imides with significantly different optical, electronic and morphological properties may be prepared. Perylene imides and their derivatives have been used in several types of organic photovoltaics, including flat-, and bulk-heterojunction devices as well as dye-sensitized solar cells. Additionally perylene imides-based copolymers or oligomers play an important role in single junction devices. In this review, the relationship between the photovoltaic performance and the structure of perylene imides is discussed.

Facile transformation of perylene tetracarboxylic acid dianhydride into strong donor-acceptor chromophores.

An efficient synthesis of 9,10-dibromo-1,6,7,12-tetrachloro-perylene-3,4-dicarboxylic acid monoimides from easily available 1,6,7,12-tetrachloro-perylene-3,4,9,10-tetracarboxylic acid dianhydride is reported. Therefrom, unprecedented perylene monoimides with pronounced donor-acceptor character were obtained via twofold aromatic amination. The halogen substituents in the 1,6,7,12-positions of perylene were removed under basic conditions. To the best of our knowledge, this is the first efficient synthetic route toward 9,10-doubly functionalized perylene-3,4-dicarboxylic acid monoimides.

Terthiophene-perylene diimides: color tuning via architecture variation.

N,N'-bisoctylperylene diimides (PDIs) have been functionalized in the 1,7-position with terthiophenes of varying architecture giving three new donor-acceptor (D-A) compounds of the same molecular weight. Different conjugation lengths, arrangements, and connections of the thiophene units within themselves and toward the PDI core have strong effects on the optical, electronic, and photochemical properties of the D-A compounds. Like jigsaw pieces joined together to give different pictures, the terthiophenes are linked to PDIs to achieve different colors. These insights into tuning color and energy levels can open new possibilities for tailoring chromophores to their desired applications, e.g., organic photovoltaics or organic field effect transistors.