Exploring cyclometalated Ir complexes as donor materials for organic solar cells.

The performance of small molecular organic photovoltaic materials is typically limited by their low exciton diffusion lengths, poor solubility, and poor energy level alignment with fullerenes so that the design and synthesis of new materials remain a top priority. To overcome these limitations, we explored the use of an iridium complex as a donor material with the potential for compatibility with solution processing, long exciton diffusion length and easy molecular modification for tunable optical or electrical properties. A bilayer device with a cyclometalated iridium complex and C60 resulted in a power conversion efficiency as high as 2.8%. Furthermore, a VOC of 1 V was achieved in the bilayer device despite an estimated exciton energy of only 1.55 eV, and the device showed minimal temperature and light intensity dependence.