Diketopyrrolopyrrole-Coumarin Conjugates for Efficient Binary Organic Solar Cells
Kerba S. More, Harshad A. Mirgane, Shyam Shankar S, Nirmala Niharika Bhuyan, Amaresh Mishra, Sheshanath V. Bhosale, Ganesh D. Shrama
Abstract
Two coumarin (Cou)-functionalized DPP derivatives, DPP-Cou and Cou-DPP-Cou, have been designed, synthesized, and characterized. The extension of the molecular backbone by an additional coumarin derivative in symmetrical Cou-DPP-Cou extends the absorption to ∼750 nm ( E g opt = 1.67 eV) compared to ∼700 nm ( E g opt = 1.78 eV) for asymmetric DPP-Cou. Thermogravimetric analysis showed higher thermal stability for symmetrical conjugates compared to the asymmetric one. Both materials showed complementary absorption spectra and well-matched Frontier molecular orbital energy levels with the low band gap fullerene-free acceptor Y7 and used as a donor in organic solar cells. After optimization using solvent vapor annealing treatment, the organic solar cells based on DPP-Cou:Y7 and Cou-DPP-Cou:Y7 attained overall power conversion efficiencies (PCE) of 9.63 and 13.48%, respectively. The improved PCE for the Cou-DPP-Cou derivative is mainly due to an appropriate morphology for faster charge extraction and lower charge recombination.