CELLO aims at developing a) thin film flexible and large area lighting sources with power efficiencies &gt;25 lm/W and lifetimes &gt;5000 hours based on light-emitting electrochemical cells (LEC) that rely on phosphorescent ionic transition metal complexes as the single active component and b) a scale-able and roll-to-roll compatible wet processes to deposit the molecular active component and the metal contact, generating fully printed devices, which will lead to an improved cost effectiveness.<br/>LECs are promising candidates for use in thin-film lighting technologies as (a) they operate at very low voltages, yielding highly power efficient devices, (b) can be processed from benign solvents, (c) have high tolerance for the active layer thickness and (d) operate with air-stable electrodes that allow for simple architectures and passivation approaches.<br/>The goals of the project are:•\tDevelopment of ionic-transition metal complexes with high solid state photoluminescence quantum yields.•\tDevelopment of roll-to-roll compatible wet processes for preparing large area, amorphous thin films of ionic transition metal complexes on flexible substrates using environmentally friendly solvents.•\tDevelopment of novel device architectures for minimizing the production effort while ensuring the highest performance levels.•\tPreparation of prototypes of large area lighting foils by successive printing of the electroluminescent materials and the metallic contacts.•\tFeasibility study for these highly novel and economic thin film lighting foils in terms of their robustness and low-cost processability for general lighting and other applications.<br/>In view of the highly inter-disciplinary tasks, CELLO has assembled a consortium comprising organic, inorganic and physical chemists, opto-electronic, materials scientists, device physicists and engineers from leading European groups. The participation of Siemens and Osram ensures a rapid transfer of CELLO into future products.