New ethynediyl-linked perylene diimide/2,1,3-benzothiadiazole conjugates as electron transporting materials for perovskite solar cells

Two new compounds BT-PDI and BT2-PDI2 were synthesized by the Sonogashira reaction between 4,7-diethynyl-2,1,3- benzothiadiazole and bromoperylene diimide derivatives. The HOMO and LUMO energy levels estimated by UV-VIS spectroscopy and cyclic voltammetry were –5.66/–3.75 and –5.33/–3.41 eV for the BT-PDI and BT2-PDI2, respectively; both compounds form high-quality and smooth coatings on the perovskite surface with the root mean square roughness values 5.95 and 7.80 nm for the BT-PDI and BT2-PDI2 films, respectively; the electron mobilities in the solid films estimated by photo-CELIV method are equal to 5.0 × 10^–5 and 3.0 × 10^–5 cm² V^–1 s^–1, respectively. Both compounds being tested as electron transport layers in perovskite solar cells showed efficiency values of 14.44 and 13.01% for BT-PDI and BT2-PDI2, respectively.