Charge transport dependent high open circuit voltage tandem organic photovoltaic cells with low temperature deposited HATCN-based charge recombination layers.

Mechanisms of charge transport between the interconnector and its neighboring layers in tandem organic photovoltaic cells have been systematically investigated by studying electronic properties of the involving interfaces with photoelectron spectroscopies and performance of the corresponding devices. The results show that charge recombination occurs at HATCN and its neighboring hole transport layers which can be deposited at low temperature. The hole transport layer plays an equal role to the interconnector itself. These insights provide guidance for the identification of new materials and the device architecture for high performance devices.

Origin of Enhanced Hole Injection in Organic Light-Emitting Diodes with an Electron-Acceptor Doping Layer: p-Type Doping or Interfacial Diffusion?

The electrical doping nature of a strong electron acceptor, 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN), is investigated by doping it in a typical hole-transport material, N,N'-bis(naphthalen-1-yl)-N,N'-diphenylbenzidine (NPB). A better device performance of organic light-emitting diodes (OLEDs) was achieved by doping NPB with HATCN. The improved performance could, in principle, arise from a p-type doping effect in the codeposited thin films. However, physical characteristics evaluations including UV-vis absorption, Fourier transform infrared absorption, and X-ray photoelectron spectroscopy demonstrated that there was no obvious evidence of charge transfer in the NPB:HATCN composite. The performance improvement in NPB:HATCN-based OLEDs is mainly attributed to an interfacial modification effect owing to the diffusion of HATCN small molecules. The interfacial diffusion effect of the HATCN molecules was verified by the in situ ultraviolet photoelectron spectroscopy evaluations.

Aqueous solution-processed GeO2: an anode interfacial layer for high performance and air-stable organic solar cells.

A simple and cheap method for depositing solution-processed GeO2 (sGeO2) film is proposed utilizing the weak solubility of GeO2 in water. X-ray photoelectron spectroscopy analysis reveals that a pure GeO2 thin film can be formed by casting its aqueous solution. This method can avoid the difficulty of vacuum evaporation by its high melting point. The sGeO2 film has been used successfully as an anode interfacial layer in poly(3-hexylthiophene) (P3HT) and indene-C60 bisadduct (IC60BA)-based bulk heterojunction organic solar cells with improved power conversion efficiency and device stability compared with that using conventional poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS); the improvement of the power conversion efficiency and the device stability are estimated to be 9% and 50%, respectively. The calculations of optical intensity in a whole cell demonstrate that a thin layer of sGeO2 could function as an optical spacer in the based bulk heterojunction (BHJ) organic solar cells (OSCs) for enhancing the light harvesting in the active layer. Interfacial evaluation by impedance spectroscopy shows that the sGeO2-based cell exists less charge carrier recombination and lower contact resistance. More importantly, the sGeO2 film processing is very simple and environmentally friendly, which has potential applications in green and low-cost organic electronics in the future.