Thermally Durable Nonfullerene Acceptor with Nonplanar Conjugated Backbone for High-Performance Organic Solar Cells

A nonfullerene acceptor (NFA) with acceptor-donor-acceptor (A-D-A) architecture, i-IEICO-2F, based on 4,9-dihydro-s-indaceno[1,2-b:5,6-b ']dithiophene as an electron-donating core and 2-(6-fluoro-2,3-dihydro-3-oxo-1H-inden-1-ylidene)-propanedinitrile as electron-withdrawing end groups, is designed and synthesized. i-IEICO-2F has a twist structure in the main conjugated chain, which causes blueshifted absorption and leads to harmonious absorption with a high bandgap donor. The bandgap of i-IEICO-2F compliments the bandgap of suitable wide bandgap donor polymers such as J52, leading to complete light absorption throughout the visible spectrum. Devices based on i-IEICO-2F exhibit optimized photovoltaic performance including an open-circuit voltage of 0.93 V, a short-circuit current density of 16.61 mA cm(-2), and a fill factor of 73%, and result in a power conversion efficiency (PCE) of 11.28%. The i-IEICO-2F-based devices reach PCEs of >11% without using any additives or post-treatments. Devices are found to be thermally stable and maintain 44% of their initial PCE after 184.5 h of continuous thermal annealing (TA) treatment at 150 degrees C. Based on UV, atomic force microscopy (AFM), and grazing incidence wide angle X-ray scattering (GIWAXS) results, i-IEICO-2F devices show almost identical morphology and molecular orientation throughout the TA treatment and excellent stability compared to other IEICO derivatives.