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

Abstract

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 °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.

Engineering the Core Units of Small‐Molecule Acceptors to Enhance the Performance of Organic Photovoltaics

“…[ 3 ] Currently, bulk heterojunction (BHJ) structures are the most prevalent and effective active‐layer designs for OPVs; they typically comprise nanometer‐scale phase‐separated blends of donor and acceptor (p‐ and n‐type) materials that form large interfacial contact areas and many pathways for carrier transport. [ 4 ] OPVs have experienced rapid development, with their power conversion efficiencies (PCEs) recently surpassing 17% for single‐junction devices. [ 5 ] The BHJ active layer morphology is affected by the relative molecular packing of the donor and acceptor [ 6 ] and, furthermore, can have a critical effect on OPV performance.…”

Recent Progress in the Design of Fused-Ring Non-Fullerene Acceptors─Relations between Molecular Structure and Optical, Electronic, and Photovoltaic Properties

“…In combination with J52, 5-158 reached a V OC of 0.96 V and a PCE of 10.5%, which is twice as high as the efficiencies of devices with the regioisomer 5-150 . Solar cells of 5-159 (INCN-F groups) showed increased PCE values from 11.3 to 12.9%, and further, those of 5-161 with the INCN-2F groups get even higher up to 13.8%, also exceeding the performance achieved with the isomer 5-147 . Electrochemical and optical properties of 5-160 (i-IEICO-F3), in which the fluorine atom is located ortho to the carbonyl group of the INCN moiety, are nearly identical to its regioisomer 5-159 .…”

High Tg Polymer Insulator Yields Organic Photovoltaic Blends with Superior Thermal Stability at 150 oC

“…It was already acknowledged in both polymer:fullerene and polymer:nonfullerene blend systems that crystallization is a key loss mechanism that results in poor thermal stability. [ 22,24‐28 ] From the viewpoint of polymer physics, glass transition temperature ( T g ) is the temperature at which a polymer turns from glassy state to rubbery state. For a given polymer:small molecule photovoltaic blend, small molecule acceptors become mobile and start forming micron‐size clusters when processing temperatures are above T g .…”