High-Efficiency and Stable Organic Solar Cells Enabled by Dual Cathode Buffer Layers

Abstract

Various cathode interface materials have been used in organic solar cells (OSCs) to realize high performance. However, most cathode interface materials have their respective weaknesses in maximizing the efficiency or stability of OSCs. Herein, three kinds of alcohol-soluble cathode interfacial materials are combined with bathocuproine (BCP) to serve as multifunctional bilayer cathode buffers for the regular OSCs, and thus greatly enhanced power conversion efficiencies over 10.11% and significantly improved device stability have been achieved. By utilizing double interlayers, both light absorption and light distribution in active layer are improved. Furthermore, double interlayers offer favorable energy-level alignment, alcohol treatment, and duplicate protection of active layer, resulting in significantly reduced leakage current, suppressed recombination, and efficient charge collection. The improved device stability is related to the blocking effect of the complex formed between BCP and the metal electrode and the additional protection effect of the underlying alcohol-soluble materials. In view of the universal use of alcohol-soluble organic electrolyte as cathode buffer layers and by courtesy of the superiority of the double cathode layers relative to the monolayer controls, the double interlayer strategy demonstrated here opens a new way to fully exploiting the potential of OSCs and is believed to be extended to a wider application.

Image-force effects on energy level alignment at electron transport material/cathode interfaces

“…[28][29][30] However, this only occurs when the molecules are deposited on clean reactive metal surfaces with low WF, such as BCP on Ag, Al, Ca, Mg. The interface dipoles created by ETMs at the surface of nonreactive metals, e.g., Au, Cu, 25 AlO x and organic films, [31][32][33][34] cannot be explained by this theory, however. Another proposed model is that ETMs with an intrinsic molecular dipole moment can create a dipole potential step through intermolecular order at the interface.…”

Role of Central Metal Ions in 8‐Hydroxyquinoline‐Doped ZnO Interfacial Layers for Improving the Performance of Polymer Solar Cells

“…Figure a displays the quantified values of the secondary electron cut‐off for the ZnO (17.19 eV), GaQ:ZnO (17.23 eV), AlQ:ZnO (17.12 eV), and MnQ:ZnO (17.11 eV) films. The corresponding WF was 4.03 eV for the ZnO film, 3.99 eV for the GaQ:ZnO film, 4.10 eV for the AlQ:ZnO film, and 4.11 eV for the MnQ:ZnO film . The WF of the GaQ:ZnO film was marginally lower than that of the other studied films.…”

“…The WF of the GaQ:ZnO film was marginally lower than that of the other studied films. A lower WF indicates the formation of electric dipoles at the interface and enhanced electron collection at the electrode, as described in Figure c . The electron transfer from metal (M) atoms to the quinoline (Q) ligand was different in accordance with different metal ions (M = Ga, Al, and Mn) having different electronegativities in ZnO .…”

Reducing Burn‐In Loss of Organic Photovoltaics by a Robust Electron‐Transporting Layer

“…[29,30] An amorphous transition metal oxide network can be obtained via hydrolysis and condensation of transition metal alkoxide. [28,[35][36][37][38][39] However, usually the thickness of the ETL should be controlled to less than ≈1 nm because of the large electrical resistance of LiF or polymer electrolytes. The ZnO layer prepared by the sol-gel process is one of widely utilized ETLs.…”