The power conversion efficiency of organic solar cells (OSCs) has made exceptionally rapid progress in the past five years owing to the emergence of fused-ring electron acceptors (FREAs). To achieve the commercialization, it is urgent to resolve the stability issues of OCSs from materials to devices. In particular, the state-of-the-art FREAs, often synthesized by Knoevenagel condensation, generally contain two exocyclic vinyl groups (CC bond) as the conjugated bridges, which inevitably exhibit an obvious electron-deficient characteristic due to the strong push-pull electronic effect. As a result, these vinyl bridges are vulnerable to nucleophile attacking and/or photooxidation, leading to poor chemical and photochemical stabilities of FREAs that easily cause the degradation of device performance. In this perspective, an in-depth understanding of the degradation mechanism of FREAs is provided, and then effective strategies reported recently are reviewed for improving the chemical and photochemical stabilities of FREAs from interfacial engineering to molecular engineering to additive engineering. Finally, a conclusion and outlook for the future design of highly efficient and stable FREAs are also presented.
The development of wide-bandgap polymer donors having complementary absorption and compatible energy levels with near-infrared (NIR) absorbing nonfullerene acceptors is highly important for realizing high-performance organic solar cells (OSCs). Herein, a new thiophene-fused diazabenzo[k]fluoranthene derivative is successfully synthesized as the electron-deficient unit to construct an efficient donor-acceptor (D-A) type alternating copolymer donor, namely, PABF-Cl, using the chlorinated benzo[1,2-b:4,5-b']dithiophene as the copolymerization unit. PABF-Cl exhibits a wide optical bandgap of 1.93 eV, a deep highest occupied molecular level of −5.36 eV, and efficient hole transport. As a result, OSCs with the best power conversion efficiency of 11.8% are successfully obtained by using PABF-Cl as the donor to blend with a NIR absorbing BTP-eC9 acceptor. This work provides a new design of electron-deficient unit for constructing high-performance D-A type polymer donors.
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