Indenothiophene-Based Wide Bandgap Copolymer for Polymer Fullerene Solar Cells with 9.01% Efficiency and 1.0 V Open Circuit Voltage

Despite the frequently renewed record high power conversion efficiencies (PCEs) in recent years, achieving single-junction polymer solar cells (PSCs) with both high PCE and large open circuit voltage (V-OC) remains a challenge because there is a trade-off between high short circuit current density (J(SC)) and large VOC values. Here, the design and synthesis of a novel donor-acceptor (D-A) copolymer (PIT2FBT) based on an asymmetric-indenothiophene donor and a difluorinated benzo[c][1,2,5] thiadiazole acceptor is demonstrated. PIT2FBT exhibits a wide optical bandgap of 1.82 eV with a large ionization potential of 5.54 eV. Through systematic morphology control and device engineering, the best performance solar cell based on PIT2FBT shows a high PCE of 9.01% in combination with a large V-proportional to of 1.0 V. To the best of our knowledge, the PCE is the highest for single-junction polymer fullerene solar cells with V(proportional to)s up to 1.0 V. At the same time, the influences of solvent additive on the active layer morphology together with the resulting device performance are investigated in-depth. These findings and detailed studies provide an important guidance to tune and optimize the morphology and photovoltaic properties of indenothiophene-based copolymers, which are promising candidates for short-wavelength absorbing materials in tandem PSCs.