Abstract
Small molecule organic solar cells (SMOSCs) have received considerable attention in recent years. However, one of the key factors limiting the performance of SMOSCs is their large energy loss (Eloss), which is typically between 0.6 and 1.0 eV, and therefore significantly higher than those of perovskite solar cells and inorganic solar cells (Eloss < 0.5 eV). Herein, we successfully report a new acceptor–donor–acceptor (A–D–A) type dimeric squaraine electron donor (D-IDTT-SQ) with a low optical band gap of 1.49 eV and deep HOMO energy level of −5.20 eV. Consequently, a high open-circuit voltage (Voc) of 0.93 V with an impressive power conversion efficiency (PCE) of 7.05\% is achieved for solution-processed bulk heterojunction SMOSCs, showing an Eloss of only 0.56 eV. This is the first report wherein SMOSCs result in such a low Eloss, while simultaneously exhibiting a considerably high Voc over 0.9 V and an excellent PCE above 7.0\%.
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