SPONTANEOUS GENERATION OF INTERLAYERS IN OPVs WITH SILVER CATHODES: ENHANCING Voc AND LIFETIME

The performance of organic photovoltaic (OPV) devices steadily increased in the recent years, with the state-of-the-art devices now reaching over 11% efficiency. A major contribution to this improvement is due to the successful engineering of the metal/organic interface by introduction of interlayers. The interlayers are generally deposited between the organic active layer and the electrodes to control the chemical interactions and energy band alignment to enhance charge extraction. Here we show a new methodology for processing interlayers by the migration of the interlayer molecules from within the film to the organic/metal interface. The driving force for this special migration is the chemical interaction between the interlayer molecules and the thermally evaporated metal atoms. Under such conditions, an interlayer is spontaneously generated during the metal deposition. Here we show that the spontaneously generated interlayers between P3HT:PCBM and a silver cathode significantly enhance the device efficiency and lifetime. The interlayer molecule used is dithiol-polyethylene-oxide (HEG-DT). The thiol/silver interactions lead to the interlayer formation, as evident from XPS analysis. In parallel, the ethylene oxide at the interface reduces the silver work function effectively enhancing the device Voc, as evident from UPS measurements. Furthermore, presence of the interlayer was shown to significantly enhance the ambient stability of non-encapsulated devices.