1. Centre for Engineered Quantum Systems; School of Mathematics and Physics; The University of Queensland; St Lucia Campus Brisbane 4072 Australia
2. Institute of Polymer Optoelectronic Materials and Devices; State Key Laboratory of Luminescent Materials and Devices; South China University of Technology; Guangzhou 510640 P. R. China
3. Optoelectronics of Organic Semiconductors; Institute for Physics and Astronomy; University of Potsdam; 14476 Potsdam-Golm Germany