Fullerenes are still among the best performing electron acceptor materials for electronic applications such as organic solar cells, organic-inorganic perovskite solar cells and transistors. We demonstrate that voltammetry is a very powerful tool for the determination of the redox potentials and thus the LUMO levels of various fullerene acceptor materials when identical conditions, i. e. same electrolyte, electrode material and potential standard, are used. The analyzed fullerene derivatives bear several types (indene, anthracene and 1,2-dimethoxymethano groups) and numbers (mono-, bis-and tris-adducts) of addends. Our systematical study enables a direct correlation of the values obtained for the individual fullerenes, and a linear relationship of the redox potential and the number of addends was found. The high lying LUMO levels of the bis-and trisadducts are favorable in terms of a high open circuit voltage in combination with polymer donors in bulk heterojunction solar cells. Considering only high LUMO values IC 60 TA and IC 70 TA are the most promising materials for organic solar cells revealing a high V OC . The bis-adducts of the fullerenes reveal LUMO levels that closely match the energy level of the widely used organometal trihalide CH 3 NH 3 PbI in perovskite solar cells.

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In order to improve the exciton utilization efficiency (η exc ) of organic lightemitting materials, we addressed the ideal donor−acceptor dihedral angle (θ D−A ) in the TADF molecule by striking a balance between two photophysical processes. One is the conversion of triplet excitons into singlet excitons, and the other is the radiative process from a low-lying excited state to the ground state. Using a combination of first-principles calculations and molecular dynamics simulations, we investigated the impact of θ D−A on the splitting energy and spin−orbit coupling between singlet and triplet excitons as well as the transition dipole moment for carbazole benzonitrile (CzBN) derivatives. By comparison with the reverse intersystem crossing rate (k rISC ), fluorescence emission rate (k r ), and η exc , we proposed a potential highest η exc (of 94.4%) with the ideal θ D−A of 77°for blue light CzBN derivatives; the calculated results have a good agreement with experimental measurement. The structure−efficiency physical connection between the molecular structure (θ D−A ) and efficiency provided an ideal parameter for a potential candidate for blue TADF-OLED materials.

Abstract-In this study, a series of aromatic aldehyde schiff base compounds were synthesized respectively by 4,4'-diaminobiphenyl and three different aromatic aldehydes. The structures of these compounds were confirmed by FT-IR, and 1H NMR. The optical properties, which were characterized by UVVis and photoluminescence spectroscopy, indicated that the fluorescence spectra were red-shift with the increase of the electron delocalization in the conjugate systems. The result showed that these schiff base compounds might have potential application as fluorescence materials.

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